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[Alexei A. Belik](https://orcid.org/0000-0001-9031-2355)

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[Two Perovskite Modifications of BiFe0.6Mn0.4O3 Prepared by High-Pressure and Post-Synthesis Annealing at Ambient Pressure](https://mdr.nims.go.jp/datasets/545a6386-43d9-465a-b7c7-e3c5b78a7f3a)

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Two Perovskite Modifications of BiFe0.6Mn0.4O3 Prepared by High-Pressure and Post-Synthesis Annealing at Ambient PressureCitation: Belik, A.A. Two PerovskiteModifications of BiFe0.6Mn0.4O3Prepared by High-Pressure andPost-Synthesis Annealing at AmbientPressure. Inorganics 2024, 12, 226.https://doi.org/10.3390/inorganics12080226Academic Editors: Shuang Liangand Mingyue ZhangReceived: 29 July 2024Revised: 16 August 2024Accepted: 16 August 2024Published: 19 August 2024Copyright: © 2024 by the author.Licensee MDPI, Basel, Switzerland.This article is an open access articledistributed under the terms andconditions of the Creative CommonsAttribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).inorganicsArticleTwo Perovskite Modifications of BiFe0.6Mn0.4O3 Preparedby High-Pressure and Post-Synthesis Annealing atAmbient PressureAlexei A. BelikResearch Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS),Namiki 1-1, Tsukuba 305-0044, Ibaraki, Japan; alexei.belik@nims.go.jpAbstract: BiFeO3-related perovskite-type materials attract a lot of attention from the viewpointof applications and fundamental science. In this work, we prepared two modifications of heavilyMn-doped BiFeO3 with the composition of BiFe0.6Mn0.4O3. A high-pressure (HP) modificationwas prepared at about 6 GPa and 1400 K. An ambient pressure (AP) modification was prepared byheating the HP modification at 780 K in the air at AP (post-synthesis annealing). Crystal structuresof both modifications and in situ transformation were investigated with synchrotron powder X-raydiffraction. The transformation started at about 700 K and finished at about 780 K. The HP mod-ification crystallized in space group Pnma with a = 5.57956 Å, b = 15.70576 Å, and c = 11.22557 Å,and the AP modification crystallized in space group Pbam with a = 5.63839 Å, b = 11.2710 Å, andc = 7.75923 Å (all parameters were at room temperature). Post-synthesis annealing of the HP mod-ification (conversion polymorphism) is the only way to prepare the Pbam modification of oxygenstoichiometric BiFe0.6Mn0.4O3. Magnetic properties of both modifications have been reported. TheNéel temperatures are TN = 350 K (HP) and TN = 335 K (AP). HP modification shows larger spincanting. Both modifications show negative magnetization phenomena at low temperatures in lowmagnetic fields.Keywords: multiferroics; doped BiFeO3; high-pressure synthesis; irreversible transformations;conversion polymorphism1. IntroductionMaterials with all possible ordered magnetic spins and electric dipoles are calledmultiferroics nowadays [1–4], even though the term ‘multiferroics’ was initially introducedonly for materials with simultaneous ferroelectric and ferromagnetic (FM) orders [5]. TheBiFeO3 perovskite is arguably the most studied multiferroic material [6], which attractedrenewed interest after the work on thin-film samples [7]. BiFeO3 belongs to the so-calledtype-I multiferroics [1–4]. In type-I multiferroics, a ferroelectric transition takes place at adifferent temperature in comparison with the temperature of a magnetic transition becausemagnetism and ferroelectricity have different origins. In BiFeO3, the ferroelectric (FE)transition takes place at TFE = 1100 K and originates from the activity of a lone-electronpair of Bi3+ cations [6]. BiFeO3 crystallizes in the space group R3c below TFE. The pureantiferromagnetic (AFM) transition occurs at the Néel temperature TN = 643 K and origi-nates from superexchange interactions between magnetic Fe3+ cations [6]. Magnetic Fe3+cations on the three-dimensional perovskite lattice usually give large magnetic transitiontemperatures above room temperature, as in RFeO3 [8]. Neighboring spins are canted inBiFeO3. However, the absence of any net FM moments in BiFeO3 originates from a longperiod of incommensurate spin ordering, which averages the total net moment to zero [6].Different crystallographic phases have close energies and compete with each otherin BiFeO3, as can be seen from a cascade of structural phase transitions under high pres-sure [9–11] and the stabilization of different phases with small amounts of doping onInorganics 2024, 12, 226. https://doi.org/10.3390/inorganics12080226 https://www.mdpi.com/journal/inorganicshttps://doi.org/10.3390/inorganics12080226https://doi.org/10.3390/inorganics12080226https://creativecommons.org/https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://www.mdpi.com/journal/inorganicshttps://www.mdpi.comhttps://orcid.org/0000-0001-9031-2355https://doi.org/10.3390/inorganics12080226https://www.mdpi.com/journal/inorganicshttps://www.mdpi.com/article/10.3390/inorganics12080226?type=check_update&version=2Inorganics 2024, 12, 226 2 of 13both Bi and Fe sublattices [12–17]. At ambient pressure (AP), solid solutions can usu-ally be prepared in whole compositional ranges from x = 0 to x = 1 in cases of (1) iso-valent doping in the Bi sublattice, for example, Bi1−xRxFeO3 with R3+ = rare-earth ele-ments [13–15] and (2) simultaneous aliovalent doping at both Bi and Fe sublattices, forexample, (1−x)BiFeO3−xPbTiO3 [18] and (1−x)BiFeO3−xBaTiO3 [19]. On the other hand,doping only at the Fe sublattice, BiFe1−xMxO3 with M = 3d transition metals can be realizedin very limited compositional ranges at AP. A maximum doping level of about x = 0.3 isrealized in the BiFe1−xMnxO3 system at AP [17,20,21]. The main reason for this seems tobe the fact that BiMO3 with other 3d transition metals (except for M = Fe) is not stable atAP [22].During two decades of intensive research on BiFeO3-related materials, different prepa-ration methods of Bi1−xRxFeO3 and BiFe1−xMxO3 have been developed and used, forexample, different modifications of a standard solid-state synthesis (e.g., rapid synthesis)in different atmospheres, high-pressure (HP) high-temperature methods, variable soft-chemistry methods, plasma syntheses, and so on. However, in the case of BiFe1−xMnxO3solid solutions, only standard solid-state synthesis in different atmospheres and HP high-temperature methods have been described in the literature.The HP high-temperature method has significant advantages because BiFe1−xMxO3solid solutions for compositional ranges from x = 0 to x = 1 can be prepared [17,23–25].This method also often gives different modifications of BiFe1−xMxO3 in comparison withAP synthesis. In addition, a “conversion polymorphism” phenomenon [23] is sometimesobserved in HP phases of BiFe1−xMxO3 when post-synthesis annealing produces newphases of BiFe1−xMxO3, which cannot be accessible using other methods.In this work, we describe such a “conversion polymorphism” phenomenon in thehigh-pressure-synthesized BiFe0.6Mn0.4O3. An HP modification was prepared at about6 GPa and 1500 K. An AP modification was prepared by heating the HP modificationat 773 K in air at AP. The HP modification crystallizes in the space group Pnma and isisostructural with some Bi1−xRxFeO3 compounds, while the AP modification crystallizesin the space group Pbam and is isostructural with an antiferroelectic phase of PbZrO3. Themagnetic properties of both modifications were studied.2. Results and DiscussionThe as-synthesized HP-BiFe0.6Mn0.4O3, crystallized in a complex PbZrO3-relatedsuperstructure√2ap × 4ap × 2√2ap (where ap (≈3.95 Å) is the parameter of the cubicperovskite subcell) with a = 5.57956(3) Å, b = 15.70576(8) Å, c = 11.22557(6) Å, and thespace group Pnma (No. 62) [17]. HP-BiFe0.6Mn0.4O3 contained a small amount of Bi2O2CO3impurity (about 1.1 weight%). HP-BiFe0.6Mn0.4O3 with heavy doping at the Fe sublatticehas the same (super)structure as Bi0.82La0.18FeO3 [13] and Bi0.85Nd0.15FeO3 [26] with smalldoping at the Bi sublattice. This fact shows that the centrosymmetric Pnma structure with√2ap × 4ap × 2√2ap is one of the competing phases with the ferroelectric R3c structure ofthe parent BiFeO3. Refined structural parameters of HP-BiFe0.6Mn0.4O3 are summarizedin Table 1, and Figure 1a shows fragments of experimental, calculated, and differencesynchrotron XRPD data after the Rietveld fit.In situ high-temperature structural studies of HP-BiFe0.6Mn0.4O3 showed that synchrotronpatterns (and superstructure reflections) did not change from 297 K to 680 K (Figure 2). How-ever, the temperature dependence of the lattice parameters of HP-BiFe0.6Mn0.4O3 showed someanomalies above 620 K (Figure 3). At 700 K, new reflections started to emerge (Figure 2). Withfurther increases in temperature, intensities of new reflections increased, while intensities ofsuperstructure reflections corresponding to the Pnma model (√2ap × 4ap × 2√2ap) decreased.Finally, at 780 K, all superstructure reflections corresponding to the Pnma model disappeared(Figure 2). All peaks at 780 K could be indexed in a√2ap × 2√2ap × 2ap superstructurewith a = 5.64743(13) Å, b = 11.2983(2) Å, c = 7.82606(5) Å, and the space group Pbam (No. 55).During cooling, the new modification remained down to 297 K; this modification can be calledAP-BiFe0.6Mn0.4O3. Refined structural parameters of AP-BiFe0.6Mn0.4O3 at 297 K and 780 KInorganics 2024, 12, 226 3 of 13are summarized in Tables 2 and 3, and Figure 1b shows the fragments of experimental, cal-culated, and difference synchrotron XRPD data after the Rietveld fit at 297 K as an example.The temperature dependence of the lattice parameters on heating and cooling is illustratedin Figures 3 and 4. The crystal structure of AP-BiFe0.6Mn0.4O3 is isostructural with theantiferroelectric phase of PbZrO3 [27,28]. This crystal structure was also reported, for exam-ple, for Bi0.8La0.2FeO3 [11], Bi0.875Pr0.125FeO3 [15], and Bi0.89Ca0.11FeO3 [16]. Therefore, thiscentrosymmetric Pbam structure with√2ap × 2√2ap × 2ap is another competing phase.Inorganics 2024, 12, x FOR PEER REVIEW 3 of 13   7.82606(5) Å, and the space group Pbam (No. 55). During cooling, the new modification remained down to 297 K; this modification can be called AP-BiFe0.6Mn0.4O3. Refined struc-tural parameters of AP-BiFe0.6Mn0.4O3 at 297 K and 780 K are summarized in Tables 2 and 3, and Figure 1b shows the fragments of experimental, calculated, and difference synchro-tron XRPD data after the Rietveld fit at 297 K as an example. The temperature dependence of the lattice parameters on heating and cooling is illustrated in Figures 3 and 4. The crystal structure of AP-BiFe0.6Mn0.4O3 is isostructural with the antiferroelectric phase of PbZrO3 [27,28]. This crystal structure was also reported, for example, for Bi0.8La0.2FeO3 [11], Bi0.875Pr0.125FeO3 [15], and Bi0.89Ca0.11FeO3 [16]. Therefore, this centrosymmetric Pbam struc-ture with √2ap × 2√2ap × 2ap is another competing phase.  Figure 1. The experimental (black crosses), calculated (red line), and difference (blue line at the bot-tom) synchrotron powder X-ray diffraction patterns of (a) HP-BiFe0.6Mn0.4O3 and (b) AP-BiFe0.6Mn0.4O3 at T = 297 K between 2° and 20°. The tick marks show possible Bragg reflection posi-tions for the main phase (brown) and Bi2O2CO3 impurity (blue) from top to bottom. Table 1. Structure parameters of HP-BiFe0.6Mn0.4O3 at 297 K refined from synchrotron XRPD data. Atom WP x/a y/b z/c Biso (Å2) Bi1 8d 0.2169(5) 0.00935(9) 0.62476(16) 1.18(5) Bi2 4c 0.2135(7) 0.25 0.6251(2) 1.37(7) Bi3 4c 0.7729(7) 0.25 0.3635(2) 1.55(7)  -0.20.00.20.40.60.82 7 12 17-0.20.00.20.40.62 7 12 17Intensity (counts/106 ) Intensity (counts/106 ) 2θ  (deg): λ = 0.420138 Å (a) HP-BiFe0.6Mn0.4O3 T = 297 K space group Pnma a = 5.57956 Å, b = 15.70576 Å, c = 11.22557 Å (b) AP-BiFe0.6Mn0.4O3 T = 297 K space group Pbam a = 5.63839 Å, b = 11.2710 Å, c = 7.75923 Å Figure 1. The experimental (black crosses), calculated (red line), and difference (blue line atthe bottom) synchrotron powder X-ray diffraction patterns of (a) HP-BiFe0.6Mn0.4O3 and (b) AP-BiFe0.6Mn0.4O3 at T = 297 K between 2◦ and 20◦. The tick marks show possible Bragg reflectionpositions for the main phase (brown) and Bi2O2CO3 impurity (blue) from top to bottom.Inorganics 2024, 12, 226 4 of 13Table 1. Structure parameters of HP-BiFe0.6Mn0.4O3 at 297 K refined from synchrotron XRPD data.Atom WP x/a y/b z/c Biso (Å2)Bi1 8d 0.2169(5) 0.00935(9) 0.62476(16) 1.18(5)Bi2 4c 0.2135(7) 0.25 0.6251(2) 1.37(7)Bi3 4c 0.7729(7) 0.25 0.3635(2) 1.55(7)FeMn1 8d 0.2397(12) 0.1227(6) 0.8779(7) 1.06(11)FeMn2 8d 0.2615(11) 0.6249(5) 0.8770(6) 0.54(10)O1 8d 0.809(4) −0.0026(12) 0.6556(18) 0.24(16)O2 4c 0.641(6) 0.25 0.653(3) =B(O1)O3 4c 0.177(7) 0.25 0.425(3) =B(O1)O4 8d 0.099(4) 0.1267(17) 0.7217(19) =B(O1)O5 8d −0.003(4) 0.3942(15) −0.0260(21) =B(O1)O6 8d 0.041(4) 0.6458(14) 0.7424(23) =B(O1)O7 8d 0.019(5) 0.3989(13) 0.516(3) =B(O1)Source: Synchrotron powder X-ray diffraction (λ = 0.42014 Å); d-space range used in the refinement:0.420–11.563 Å. Crystal system: orthorhombic; space group Pnma (No 62); Z = 16. Molecular weight:312.458 g/mol. The occupation factors, g, of all Bi and O sites, are unity; g = 0.6Fe + 0.4Mn for FeMn1 and FeMn2.WP: Wyckoff position. Impurity: Bi2O2CO3 (1.1 wt.%). a = 5.57956(3) Å, b =15.70576(8) Å, c = 11.22557(6) Å, andV = 983.711 (9) Å3; Rwp = 9.02%, Rp = 6.43%, RB = 5.14%, and RF = 6.78%; ρcal = 8.439 g/cm3.Table 2. Structure parameters of AP-BiFe0.6Mn0.4O3 at 297 K refined from synchrotron XRPD data.Atom WP x/a y/b z/c Biso (Å2)Bi1 4g 0.2431(3) 0.3807(3) 0 2.15(6)Bi2 4h 0.2061(3) 0.3676(2) 0.5 0.32(3)FeMn 8i 0.2552(6) 0.1239(14) 0.2487(13) 0.80(5)O1 4g 0.241(4) 0.162(3) 0 1.8(9)O2 4h 0.338(5) 0.093(3) 0.5 1.2(7)O3 8i 0.078(4) 0.2649(16) 0.275(3) 1.7(5)O4 4f 0 0.5 0.188(3) 1.3(7)O5 4e 0 0 0.202(4) 2.4(8)Source: Synchrotron powder X-ray diffraction (λ = 0.42014 Å); d-space range used in the refinement:0.420–11.563 Å. Crystal system: orthorhombic; space group Pbam (No. 55); Z = 8. Molecular weight:312.458 g/mol. The occupation factors, g, of all Bi and O sites, are unity; g = 0.6Fe + 0.4Mn for FeMn. WP:Wyckoff position. Impurity: Bi2O2CO3 (1.1 wt.%). a = 5.63839(12) Å, b = 11.2710(2) Å, c = 7.75923(8) Å, andV = 493.103(15) Å3; Rwp = 11.93%, Rp = 8.40%, RB = 4.92%, and RF = 2.66%; ρcal = 8.418 g/cm3.Table 3. Structure parameters of AP-BiFe0.6Mn0.4O3 at 780 K refined from synchrotron XRPD data.Atom WP x/a y/b z/c Biso (Å2)Bi1 4g 0.2383(4) 0.3786(5) 0 3.31(13)Bi2 4h 0.2141(5) 0.3700(4) 0.5 1.91(9)FeMn 8i 0.2524(9) 0.1246(25) 0.2499(17) 1.56(6)O1 4g 0.257(5) 0.170(5) 0 2.3 (3)O2 4h 0.304(6) 0.091(5) 0.5 =B(O1)O3 8i 0.075(4) 0.2678(19) 0.271(4) =B(O1)O4 4f 0 0.5 0.185(4) =B(O1)O5 4e 0 0 0.206(4) =B(O1)Source: Synchrotron powder X-ray diffraction (λ = 0.42014 Å); d-space range used in the refinement:0.549–11.563 Å. Crystal system: orthorhombic; space group Pbam (No. 55); Z = 8. Molecular weight:312.458 g/mol. The occupation factors, g, of all Bi and O sites, are unity; g = 0.6Fe + 0.4Mn for FeMn. WP:Wyckoff position. Impurity: Bi2O2CO3 (1.1 wt.%). a = 5.64743(13) Å, b = 11.2983(2) Å, c = 7.82606(5) Å, andV = 499.353(16) Å3; Rwp = 10.94%, Rp = 7.43%, RB = 5.81%, and RF = 4.97%; ρcal = 8.312 g/cm3.Inorganics 2024, 12, 226 5 of 13Inorganics 2024, 12, x FOR PEER REVIEW 5 of 13    Figure 2. Temperature evolution of synchrotron powder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3 at selected temperatures. The zoomed parts emphasizing superstructure reflections are shown. Stars mark reflections from Bi2O2CO3 impurity. Black circles show characteristic reflec-tions from HP-BiFe0.6Mn0.4O3, and crosses show a characteristic reflection from AP-BiFe0.6Mn0.4O3.  Figure 3. (Up) Temperature dependence of the lattice parameters of HP-BiFe0.6Mn0.4O3 on heating. (Down) Temperature dependence of the lattice parameters of AP-BiFe0.6Mn0.4O3 on heating (black symbols) and cooling (blue symbols). Numbers show weight fractions (in%) of the corresponding phases. 3 4 5 6 7 8 9 10 11300 K 700 K 720 K 740 K 760 K 780 K * * * * * • • • • • 2θ  (deg): λ = 0.420138 Å *: Bi2O2CO3 * × × × × × Pbam Pnma 15.7015.7115.7215.7315.7415.75300 400 500 600 700 80011.2211.2311.2411.2511.2611.2711.28300 400 500 600 700 8005.5705.5805.5905.6005.6105.6205.630300 400 500 600 700 8005.6365.646300 400 500 600 700 80011.2711.2811.2911.30300 400 500 600 700 8007.7507.7607.7707.7807.7907.8007.8107.8207.8307.840300 400 500 600 700 800Temperature (K) Lattice parameters (Å) Lattice parameters (Å) a(Pnma) b(Pnma) c(Pnma) a(Pbam) b(Pbam) c(Pbam) 30 % 50 % 100 % 50 % 70 % 100 % 100 % cooling heating Figure 2. Temperature evolution of synchrotron powder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3at selected temperatures. The zoomed parts emphasizing superstructure reflections are shown. Starsmark reflections from Bi2O2CO3 impurity. Black circles show characteristic reflections from HP-BiFe0.6Mn0.4O3, and crosses show a characteristic reflection from AP-BiFe0.6Mn0.4O3.Inorganics 2024, 12, x FOR PEER REVIEW 5 of 13    Figure 2. Temperature evolution of synchrotron powder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3 at selected temperatures. The zoomed parts emphasizing superstructure reflections are shown. Stars mark reflections from Bi2O2CO3 impurity. Black circles show characteristic reflec-tions from HP-BiFe0.6Mn0.4O3, and crosses show a characteristic reflection from AP-BiFe0.6Mn0.4O3.  Figure 3. (Up) Temperature dependence of the lattice parameters of HP-BiFe0.6Mn0.4O3 on heating. (Down) Temperature dependence of the lattice parameters of AP-BiFe0.6Mn0.4O3 on heating (black symbols) and cooling (blue symbols). Numbers show weight fractions (in%) of the corresponding phases. 3 4 5 6 7 8 9 10 11300 K 700 K 720 K 740 K 760 K 780 K * * * * * • • • • • 2θ  (deg): λ = 0.420138 Å *: Bi2O2CO3 * × × × × × Pbam Pnma 15.7015.7115.7215.7315.7415.75300 400 500 600 700 80011.2211.2311.2411.2511.2611.2711.28300 400 500 600 700 8005.5705.5805.5905.6005.6105.6205.630300 400 500 600 700 8005.6365.646300 400 500 600 700 80011.2711.2811.2911.30300 400 500 600 700 8007.7507.7607.7707.7807.7907.8007.8107.8207.8307.840300 400 500 600 700 800Temperature (K) Lattice parameters (Å) Lattice parameters (Å) a(Pnma) b(Pnma) c(Pnma) a(Pbam) b(Pbam) c(Pbam) 30 % 50 % 100 % 50 % 70 % 100 % 100 % cooling heating Figure 3. (Up) Temperature dependence of the lattice parameters of HP-BiFe0.6Mn0.4O3 on heat-ing. (Down) Temperature dependence of the lattice parameters of AP-BiFe0.6Mn0.4O3 on heating(black symbols) and cooling (blue symbols). Numbers show weight fractions (in%) of the correspond-ing phases.Inorganics 2024, 12, 226 6 of 13Inorganics 2024, 12, x FOR PEER REVIEW 6 of 13    Figure 4. Temperature dependence of the normalized lattice parameters of HP-BiFe0.6Mn0.4O3 (Pnma) on heating and AP-BiFe0.6Mn0.4O3 (Pbam) on cooling. We note that the Pnma model with the √2ap × 4ap × 2√2ap superstructure is a direct subgroup of the Pbam model with the √2ap × 2√2ap × 2ap superstructure. In many cases, additional superstructure reflections of the Pnma model are very weak. Therefore, a real Pnma model was sometimes replaced by a simplified Pbam model to obtain reliable, re-fined structural parameters [29], as the Pnma model has 32 refined fractional coordinates of atoms, while the Pbam model has 16 such parameters. However, in the case of BiFe0.6Mn0.4O3, the two modifications were quite different as the fundamental perovskite lattice parameters (ap) were different (Figure 4), and the reflection splitting of strong fun-damental reflections was different at room temperature (Figures 1 and 5). Therefore, the AP-BiFe0.6Mn0.4O3 modification could not be considered as a simplified version of the HP-BiFe0.6Mn0.4O3 modification.  Figure 5. Zoomed parts (to emphasize superstructure reflections) of room-temperature synchrotron powder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3 and AP-BiFe0.6Mn0.4O3. Stars mark reflections from Bi2O2CO3 impurity. The (hkl) indexes of main superstructure reflections are given. Intensities were normalized to 1, and data for the AP modification were shifted by +0.03 (or 3%). 3.873.903.933.963.99300 400 500 600 700 800Lattice parameters (Å) Temperature (K) a/√2(Pnma) b/4(Pnma) c/2√2(Pnma) a/√2(Pbam) b/2√2(Pbam) c/2(Pbam) heating cooling   0.000.020.040.060.084 5 6 7 8 9 10 112θ  (deg): λ = 0.420138 Å HP-BiFe0.6Mn0.4O3 T = 297 K AP-BiFe0.6Mn0.4O3 T = 297 K * * * * * * * * * * * *: Bi2O2CO3 Intensity  110 021 111 130 112 131 210 211 132 141 212 231 101 111 031 022 013 131 042 103 141 051 201 133 151 143 053 124 062 203 241 Figure 4. Temperature dependence of the normalized lattice parameters of HP-BiFe0.6Mn0.4O3 (Pnma)on heating and AP-BiFe0.6Mn0.4O3 (Pbam) on cooling.We note that the Pnma model with the√2ap × 4ap × 2√2ap superstructure is a directsubgroup of the Pbam model with the√2ap × 2√2ap × 2ap superstructure. In many cases,additional superstructure reflections of the Pnma model are very weak. Therefore, a realPnma model was sometimes replaced by a simplified Pbam model to obtain reliable, refinedstructural parameters [29], as the Pnma model has 32 refined fractional coordinates of atoms,while the Pbam model has 16 such parameters. However, in the case of BiFe0.6Mn0.4O3, thetwo modifications were quite different as the fundamental perovskite lattice parameters(ap) were different (Figure 4), and the reflection splitting of strong fundamental reflectionswas different at room temperature (Figures 1 and 5). Therefore, the AP-BiFe0.6Mn0.4O3modification could not be considered as a simplified version of the HP-BiFe0.6Mn0.4O3modification.Inorganics 2024, 12, x FOR PEER REVIEW 6 of 13    Figure 4. Temperature dependence of the normalized lattice parameters of HP-BiFe0.6Mn0.4O3 (Pnma) on heating and AP-BiFe0.6Mn0.4O3 (Pbam) on cooling. We note that the Pnma model with the √2ap × 4ap × 2√2ap superstructure is a direct subgroup of the Pbam model with the √2ap × 2√2ap × 2ap superstructure. In many cases, additional superstructure reflections of the Pnma model are very weak. Therefore, a real Pnma model was sometimes replaced by a simplified Pbam model to obtain reliable, re-fined structural parameters [29], as the Pnma model has 32 refined fractional coordinates of atoms, while the Pbam model has 16 such parameters. However, in the case of BiFe0.6Mn0.4O3, the two modifications were quite different as the fundamental perovskite lattice parameters (ap) were different (Figure 4), and the reflection splitting of strong fun-damental reflections was different at room temperature (Figures 1 and 5). Therefore, the AP-BiFe0.6Mn0.4O3 modification could not be considered as a simplified version of the HP-BiFe0.6Mn0.4O3 modification.  Figure 5. Zoomed parts (to emphasize superstructure reflections) of room-temperature synchrotron powder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3 and AP-BiFe0.6Mn0.4O3. Stars mark reflections from Bi2O2CO3 impurity. The (hkl) indexes of main superstructure reflections are given. Intensities were normalized to 1, and data for the AP modification were shifted by +0.03 (or 3%). 3.873.903.933.963.99300 400 500 600 700 800Lattice parameters (Å) Temperature (K) a/√2(Pnma) b/4(Pnma) c/2√2(Pnma) a/√2(Pbam) b/2√2(Pbam) c/2(Pbam) heating cooling   0.000.020.040.060.084 5 6 7 8 9 10 112θ  (deg): λ = 0.420138 Å HP-BiFe0.6Mn0.4O3 T = 297 K AP-BiFe0.6Mn0.4O3 T = 297 K * * * * * * * * * * * *: Bi2O2CO3 Intensity  110 021 111 130 112 131 210 211 132 141 212 231 101 111 031 022 013 131 042 103 141 051 201 133 151 143 053 124 062 203 241 Figure 5. Zoomed parts (to emphasize superstructure reflections) of room-temperature synchrotronpowder X-ray diffraction patterns of HP-BiFe0.6Mn0.4O3 and AP-BiFe0.6Mn0.4O3. Stars mark re-flections from Bi2O2CO3 impurity. The (hkl) indexes of main superstructure reflections are given.Intensities were normalized to 1, and data for the AP modification were shifted by +0.03 (or 3%).Inorganics 2024, 12, 226 7 of 13Figure 6 shows the crystal structures of HP-BiFe0.6Mn0.4O3, AP-BiFe0.6Mn0.4O3, andPbZrO3 (at room temperature) for comparison [28]. (FeMn)O6 octahedra are stronglydistorted in both modifications; a similar effect is observed for TiO6 octahedra in PbZrO3.These features can be explained by the formation of strong covalent Bi–O and Pb–O bondsoriginating from the stereochemical activity of the lone pair of Bi3+ and Pb2+ cations. Inother words, elongated (FeMn)–O or Zr–O bonds are simultaneously involved in shortBi–O or Pb–O bonds, respectively [17]. The HP synthesis method usually stabilizes amodification with higher density. The density of HP-BiFe0.6Mn0.4O3 (8.439 g/cm3) wasindeed slightly higher than that of AP-BiFe0.6Mn0.4O3 (8.418 g/cm3) (Tables 1 and 2). Toachieve higher density and to accommodate the lone pair of Bi3+, an additional octahedralrotation along the b axis was necessary (Figure 6c), resulting in a superstructure and astressed structure in HP-BiFe0.6Mn0.4O3. Heating at AP results in the release of stress. Thetransformation of HP-BiFe0.6Mn0.4O3 into AP-BiFe0.6Mn0.4O3 involves small rotations of(FeMn)O6 octahedra (Figure 6b,c) and small shifts of Bi3+ cations.   (c) HP-BiFe0.6Mn0.4O3 (b) AP-BiFe0.6Mn0.4O3 (a) PbZrO3 Bi1 Bi3 Fe1 Fe2 a c a b Bi1 Bi2 Fe Zr Pb1 Pb2 Figure 6. Fragments of crystal structures of (a) PbZrO3 (at room temperature [28]), (b) AP-BiFe0.6Mn0.4O3,and (c) HP-BiFe0.6Mn0.4O3 (Bi2 atoms are hidden by Bi1 and Bi3). Arrows in panel (a) show the displace-ments of Pb2+ inside cavities. For simplicity, octahedral sites are marked as Fe, Fe1, and Fe2.No clear DSC anomalies were observed during the first round of heating of HP-BiFe0.6Mn0.4O3, suggesting that the thermal effect of the HP-to-AP transformation wasvery weak. The absence of any DSC anomalies could also be related to the fact that the HP-to-AP transformation occurred in a wide temperature range from 700 K to 780 K (Figure 2),preventing any detectable thermal effect. No clear DSC anomalies were observed duringthe first cooling of the already-formed AP-BiFe0.6Mn0.4O3, and no DSC anomalies weredetected during the second DSC run on the already-formed AP-BiFe0.6Mn0.4O3. This factsuggests that AP-BiFe0.6Mn0.4O3 did not undergo any structural phase transitions between297 K and 773 K. In the case of BiFe0.6Mn0.4O3, we observed a full transformation of an HPstructure into another AP structure. In other members of HP-BiFe1−xMnxO3 solid solutions,partial transformations into different modifications were reported [30,31].Temperature-dependent magnetic measurements showed that the Néel tempera-tures were TN = 350 K for HP-BiFe0.6Mn0.4O3 and TN = 335 K for AP-BiFe0.6Mn0.4O3(Figures 7 and 8). M versus H measurements showed that HP-BiFe0.6Mn0.4O3 had largerspin canting, especially at T = 5 K, as a clear hysteresis opened up (Figures 9 and 10). AtT = 100, 200, and 300 K, the M versus H curves of HP-BiFe0.6Mn0.4O3 were nearly linearwith narrow cigar-type hysteresis, suggesting that spin canting was quite small. At T = 5,100, 200, and 300 K, the M versus H curves of AP-BiFe0.6Mn0.4O3 were almost linear, sug-gesting nearly complete AFM states. Above TN, at T = 400 K, the M versus H curves of bothmodifications were linear because of the paramagnetic state (Figure 11) and coincided witheach other; in other words, the M versus H curves were independent of the crystal structure.Exchange-bias-like effects were observed on the M versus H curves: at T = 5 K (negativeexchange-bias-like effect) in AP-BiFe0.6Mn0.4O3 and at T = 100 K (positive exchange-bias-like effect) and 200 K (negative exchange-bias-like effect) in HP-BiFe0.6Mn0.4O3 (Figure 10).Inorganics 2024, 12, 226 8 of 13Exchange-bias-like effects were observed in other BiFeO3-based solid solutions [24,32,33].In many cases, the “extrinsic” origins of exchange-bias-like effects were suggested, suchas the presence of an antiferromagnetic core and a diluted antiferromagnetic shell [32] ornon-uniform structure distortions and magnetic phase separation [33].Inorganics 2024, 12, x FOR PEER REVIEW 8 of 14   = 5 K (negative exchange-bias-like effect) in AP-BiFe0.6Mn0.4O3 and at T = 100 K (positive exchange-bias-like effect) and 200 K (negative exchange-bias-like effect) in HP-BiFe0.6Mn0.4O3 (Figure 10). Exchange-bias-like effects were observed in other BiFeO3-based solid solutions [24,32,33]. In many cases, the “extrinsic” origins of exchange-bias-like effects were suggested, such as the presence of an antiferromagnetic core and a diluted antiferromagnetic shell [32] or non-uniform structure distortions and magnetic phase separation [33].  Figure 7. Magnetic properties of virgin HP-BiFe0.6Mn0.4O3 (Pnma) (a pellet of 41.12 mg). Field-cooled on cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are shown. The first run was measured from 300 K to 2 K and from 2 K to 300 K. The second run was measured from 300 K to 2 K and from 2 K to 400 K. The third run was measured from 400 K to 2 K and from 2 K to 400 K. Insets show the zoomed parts. The magnetic field remained the same (unchanged) through all three runs.    -1.4-1.2-1.0-0.8-0.6-0.4-0.20.00 50 100 150 200 250 300 350 4000.0000.0050.0100.0150 50 100 150 200 250 300 350 400FCC, 1, from 300 K to 2 KFCW, 1, from 2 K to 300 KFCC, 2, from 300 K to 2 KFCW, 2, from 2 K to 400 KFCC, 3, from 400 K to 2 KFCW, 3, from 2 K to 400 KTemperature (K) TN = 350 K H = 100 Oe HP-BiFe0.6Mn0.4O3  (emumol−1Oe−1)   -0.010.000.010.020.030.040.050.060.070.080 50 100 150 200 250 300 350 4000.000.01FCC, 100 Oe, DSCFCW, 100 Oe, DSCFCC, 100 OeFCW, 100 Oe (emumol−1Oe−1)  (emumol −1Oe−1) Temperature (K) AP-BiFe0.6Mn0.4O3 TN = 335 K Figure 7. Magnetic properties of virgin HP-BiFe0.6Mn0.4O3 (Pnma) (a pellet of 41.12 mg). Field-cooledon cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are shown.The first run was measured from 300 K to 2 K and from 2 K to 300 K. The second run was measuredfrom 300 K to 2 K and from 2 K to 400 K. The third run was measured from 400 K to 2 K and from 2 Kto 400 K. Insets show the zoomed parts. The magnetic field remained the same (unchanged) throughall three runs.Inorganics 2024, 12, x FOR PEER REVIEW 8 of 13   exchange-bias-like effect) in AP-BiFe0.6Mn0.4O3 and at T = 100 K (positive exchange-bias-like effect) and 200 K (negative exchange-bias-like effect) in HP-BiFe0.6Mn0.4O3 (Figure 10). Exchange-bias-like effects were observed in other BiFeO3-based solid solutions [24,32,33]. In many cases, the “extrinsic” origins of exchange-bias-like effects were suggested, such as the presence of an antiferromagnetic core and a diluted antiferromagnetic shell [32] or non-uniform structure distortions and magnetic phase separation [33].  Figure 7. Magnetic properties of virgin HP-BiFe0.6Mn0.4O3 (Pnma) (a pellet of 41.12 mg). Field-cooled on cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are shown. The first run was measured from 300 K to 2 K and from 2 K to 300 K. The second run was measured from 300 K to 2 K and from 2 K to 400 K. The third run was measured from 400 K to 2 K and from 2 K to 400 K. Insets show the zoomed parts. The magnetic field remained the same (unchanged) through all three runs.  Figure 8. Magnetic properties of AP-BiFe0.6Mn0.4O3 (Pbam). Field-cooled on cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are presented. The data for two samples  -1.4-1.2-1.0-0.8-0.6-0.4-0.20.00 50 100 150 200 250 300 350 4000.0000.0050.0100.0150 50 100 150 200 250 300 350 400FCC, 1, from 300 K to 2 KFCW, 1, from 2 K to 300 KFCC, 2, from 300 K to 2 KFCW, 2, from 2 K to 400 KFCC, 3, from 400 K to 2 KFCW, 3, from 2 K to 400 KTemperature (K) TN = 350 K H = 100 Oe HP-BiFe0.6Mn0.4O3 χ (emu×mol−1 ×Oe−1 )  -0.010.000.010.020.030.040.050.060.070.080 50 100 150 200 250 300 350 4000.000.01FCC, 100 Oe, DSCFCW, 100 Oe, DSCFCC, 100 OeFCW, 100 Oeχ (emu×mol−1 ×Oe−1 ) χ (emu×mol −1×Oe−1) Temperature (K) AP-BiFe0.6Mn0.4O3 TN = 335 K Figure 8. Magnetic properties of AP-BiFe0.6Mn0.4O3 (Pbam). Field-cooled on cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are presented. The data for two samplesare shown: an AP-BiFe0.6Mn0.4O3 sample prepared in a furnace (a pellet of 41.12 mg) is shown byblue triangles; an AP-BiFe0.6Mn0.4O3 sample prepared in a DSC experiment is shown by black circles(powder of 9.00 mg). The right-hand axis gives the same FCC curve for an AP-BiFe0.6Mn0.4O3 sampleprepared in a furnace.Inorganics 2024, 12, 226 9 of 13Inorganics 2024, 12, x FOR PEER REVIEW 9 of 14   Figure 8. Magnetic properties of AP-BiFe0.6Mn0.4O3 (Pbam). Field-cooled on cooling (FCC) and field-cooled on warming (FCW) χ versus T curves at H = 100 Oe are presented. The data for two samples are shown: an AP-BiFe0.6Mn0.4O3 sample prepared in a furnace (a pellet of 41.12 mg) is shown by blue triangles; an AP-BiFe0.6Mn0.4O3 sample prepared in a DSC experiment is shown by black circles (powder of 9.00 mg). The right-hand axis gives the same FCC curve for an AP-BiFe0.6Mn0.4O3 sample prepared in a furnace.  Figure 9. Comparison of magnetic properties of HP-BiFe0.6Mn0.4O3 (Pnma) and AP-BiFe0.6Mn0.4O3 (Pbam) (pellets of 41.12 mg): M versus H curves at (a) T = 5 K, (b) T = 100 K, (c) T = 200 K, and (d) T = 300 K.    -0.3-0.2-0.10.00.10.20.3-80 -60 -40 -20 0 20 40 60 805 K, AP5 K, HP-0.12-0.060.000.060.12-80 -60 -40 -20 0 20 40 60 80100 K, AP100 K, HP-0.08-0.06-0.04-0.020.000.020.040.060.08-80 -60 -40 -20 0 20 40 60 80200 K, AP200 K, HP-0.06-0.04-0.020.000.020.040.06-80 -60 -40 -20 0 20 40 60 80300 K, AP300 K, HPMagnetization  (B / f.u.) Magnetic Field (kOe) (a) (b) (c) (d) Figure 9. Comparison of magnetic properties of HP-BiFe0.6Mn0.4O3 (Pnma) and AP-BiFe0.6Mn0.4O3(Pbam) (pellets of 41.12 mg): M versus H curves at (a) T = 5 K, (b) T = 100 K, (c) T = 200 K, and(d) T = 300 K.   -0.006-0.0030.0000.0030.006-8 -4 0 4 8300 K, AP300 K, HP-0.008-0.0040.0000.0040.008-8 -4 0 4 8200 K, AP200 K, HP-0.012-0.0060.0000.0060.012-8 -4 0 4 8100 K, AP100 K, HP-0.04-0.020.000.020.04-8 -4 0 4 85 K, AP5 K, HPMagnetization  (µB / f.u.) Magnetic Field (kOe) (a) (b) (c) (d) Figure 10. Comparison of magnetic properties of HP-BiFe0.6Mn0.4O3 (Pnma) and AP-BiFe0.6Mn0.4O3(Pbam) (pellets of 41.12 mg): the zoomed parts of the M versus H curves are shown between −8 kOeand 8 kOe at (a) T = 5 K, (b) T = 100 K, (c) T = 200 K, and (d) T = 300 K.Inorganics 2024, 12, 226 10 of 13Inorganics 2024, 12, x FOR PEER REVIEW 11 of 14    Figure 11. Comparison of magnetic properties of HP-BiFe0.6Mn0.4O3 (Pnma) and AP-BiFe0.6Mn0.4O3 (Pbam) (pellets of 41.12 mg): (a) M versus H curves between −70 kOe and 70 kOe at T = 400 K and (b) zoomed parts of the M versus H curves between −8 kOe and 8 kOe at T = 400 K. HP-BiFe0.6Mn0.4O3 showed peculiar magnetic susceptibility (χ = M/H) curves at H = 100 Oe (Figure 7). When a virgin sample (meaning a sample taken directly after the synthesis; in other words, a sample that was not used for any magnetic measurements beforehand) was measured below its TN (between 2 K and 300 K), the χ values were positive, and the FCC and FCW curves matched with each other and coincided on cycling. A sharp upturn was observed on the χ versus T curves below 120 K, suggesting the development of a weak FM moment in agreement with the M versus H curve at 5 K (Figure 9a). However, when the sample was heated above its TN (up to 400 K), the χ values on the FCC and FCW curves were negative below 150 K, demonstrating a strong negative magnetization effect. Absolute M values (at T = 5 K) were about 70 times larger when measured from 400 K in comparison with the measurement from 300 K. It is probably for this reason that no anomalies were observed near 120 K when measurements were performed from 400 K because strong negative magnetization hid a weak upturn. In addition, the FCC and FCW curves of HP-BiFe0.6Mn0.4O3 did not match above TN as would be expected in a paramagnetic state, but their merging gradually took place on approaching 400 K. This observation could suggest that there are some ferromagnetic-like    -0.050-0.0250.0000.0250.050-80 -60 -40 -20 0 20 40 60 80400 K, AP400 K, HP-0.0050-0.00250.00000.00250.0050-8 -4 0 4 8400 K, AP400 K, HPMagnetization  (B / f.u.) Magnetization  (B / f.u.) Magnetic Field (kOe) (a) (b) Figure 11. Comparison of magnetic properties of HP-BiFe0.6Mn0.4O3 (Pnma) and AP-BiFe0.6Mn0.4O3(Pbam) (pellets of 41.12 mg): (a) M versus H curves between −70 kOe and 70 kOe at T = 400 K and(b) zoomed parts of the M versus H curves between −8 kOe and 8 kOe at T = 400 K.HP-BiFe0.6Mn0.4O3 showed peculiar magnetic susceptibility (χ = M/H) curves atH = 100 Oe (Figure 7). When a virgin sample (meaning a sample taken directly after thesynthesis; in other words, a sample that was not used for any magnetic measurementsbeforehand) was measured below its TN (between 2 K and 300 K), the χ values were positive,and the FCC and FCW curves matched with each other and coincided on cycling. A sharpupturn was observed on the χ versus T curves below 120 K, suggesting the development ofa weak FM moment in agreement with the M versus H curve at 5 K (Figure 9a). However,when the sample was heated above its TN (up to 400 K), the χ values on the FCC andFCW curves were negative below 150 K, demonstrating a strong negative magnetizationeffect. Absolute M values (at T = 5 K) were about 70 times larger when measured from400 K in comparison with the measurement from 300 K. It is probably for this reasonthat no anomalies were observed near 120 K when measurements were performed from400 K because strong negative magnetization hid a weak upturn. In addition, the FCCand FCW curves of HP-BiFe0.6Mn0.4O3 did not match above TN as would be expected ina paramagnetic state, but their merging gradually took place on approaching 400 K. Thisobservation could suggest that there are some ferromagnetic-like short-range correlationsabove TN. On the other hand, the FCC and FCW curves of AP-BiFe0.6Mn0.4O3 almostmerged above TN.Inorganics 2024, 12, 226 11 of 13The magnetic properties of two AP-BiFe0.6Mn0.4O3 samples are shown in Figure 8: onesample was obtained in a furnace; and another sample was obtained in a DSC experiment(see the experimental part). Both samples showed a magnetic transition at the sametemperature of TN = 335 K with different magnitudes of upturns below TN. But, for bothsamples, the upturn below TN was quite small, suggesting the development of small spincanting. The AP-BiFe0.6Mn0.4O3 sample prepared in a DSC experiment showed a negativemagnetization effect below 30 K. The absence of a negative magnetization effect in theAP-BiFe0.6Mn0.4O3 sample prepared in a furnace suggests that this effect can be called“extrinsic” [24] when it is observed in some samples of AP-BiFe0.6Mn0.4O3.The introduction of Mn3+ cations into BiFeO3 changes the crystal structure from a certainconcentration of Mn3+ cations due to the existence of several competing structures and mono-tonically suppresses TN from 643 K in BiFeO3 to about 270 K in BiFe0.5Mn0.5O3 [17,24,25]. Themagnetic transition temperatures of BiFe1−xMnxO3 remain relatively high because of largeconcentrations of Fe3+ cations. Magnetic properties of BiFeO3 [17] and AP-BiFe0.6Mn0.4O3were qualitatively similar in the sense that they both showed nearly pure AFM behaviordespite their different crystal structures. The temperature dependence of magnetic suscepti-bility exhibited a sharp rise just below TN in both compounds, indicating an initial develop-ment of uncompensated moments, but these uncompensated moments were suppressed atlower temperatures.3. Materials and MethodsThe HP modification of BiFe0.6Mn0.4O3 was prepared from a stoichiometric mixtureof Bi2O3 (Rare Metallic Co., Tokyo, Japan, 99.9999%), Fe2O3 (Rare Metallic Co., Tokyo,Japan, 99.999%), and Mn2O3. Single-phase Mn2O3 was prepared from a commercial MnO2chemical (Rare Metallic Co., Tokyo, Japan, 99.99%) by annealing in the air at 923 K for24 h. The synthesis was performed at about 6 GPa and about 1400 K for 1.5 h in a sealedAu capsule using a belt-type HP instrument. After annealing at 1400 K, the sample wascooled down to room temperature by turning off the heating current, and the pressure wasslowly released. As the used synthesis conditions for HP-BiFe0.6Mn0.4O3 gave high-qualitysamples, we did not investigate the effects of synthesis conditions on the quality of HP-BiFe0.6Mn0.4O3 and pressure–temperature stability ranges of HP-BiFe0.6Mn0.4O3 (it wasalso out of the scope of the present work). But we did note that the pressure–temperaturestability ranges of BiFe1−xMnxO3 solid solutions can be relatively large as a lower pressureof 5 GPa and lower temperature of 1073 K have been used in the literature [25]. The APmodification of BiFe0.6Mn0.4O3 was prepared by heating HP-BiFe0.6Mn0.4O3 in the air atAP at 773 K for 10 min (with a heating–cooling rate of 10 K/min).X-ray powder diffraction (XRPD) data were collected at room temperature on a Mini-Flex600 diffractometer (Rigaku, Tokyo, Japan) using CuKα radiation (2θ range of 8–100◦,a step width of 0.02◦, and a scan speed of 2◦/min). Synchrotron XRPD data of HP-BiFe0.6Mn0.4O3 were collected at 297 K upon heating to 780 K and cooling to 297 K usingthe beamline BL02B2 [34] of SPring-8, Japan. Intensity data were taken between 2.08◦ and78.21◦ at a 0.006◦ interval in 2θ using a wavelength of λ = 0.420138 Å; however, data upto 60◦ (at 297 K) were used in the Rietveld analysis as no experimental reflections wereobserved above 60◦. The measurement times were 300 s at 297 K and 780 K and 60 s forother temperatures. The sample was placed into an open Lindemann glass capillary tube(inner diameter: 0.1 mm), which was rotated during measurements. The Rietveld analysisof all XRPD data was performed using the RIETAN-2000 program [35].Magnetic measurements were performed on a SQUID magnetometer (Quantum De-sign MPMS3, San Diego, CA, USA) between 2 and 300 K (or 400 K) in an applied fieldof 100 Oe on cooling (FCC: field-cooled on cooling) and warming (FCW: field-cooled onwarming). Isothermal magnetization measurements for M versus H were performed from70 kOe to −70 kOe and from −70 kOe to 70 kOe starting from 300 K, then at 200 K, 100 K,5 K, and 400 K; the temperature was changed under the applied field of 70 kOe. In otherwords, after finishing M versus H measurements at, for example, 300 K, the field was keptInorganics 2024, 12, 226 12 of 13at 70 kOe, and the temperature was changed to 200 K. A piece of an HP-BiFe0.6Mn0.4O3pellet (41.12 mg) was used in the magnetic measurements. This pellet was then transformedto AP-BiFe0.6Mn0.4O3 (by annealing in a furnace in the air at AP at 773 K for 10 min asdescribed above), and the same pellet was used in magnetic measurements.Differential scanning calorimetry (DSC) curves of a powder sample of HP-BiFe0.6Mn0.4O3were recorded on a Mettler Toledo DSC1 STARe system between 297 K and 773 K in an openAl capsule with a heating/cooling rate of 10 K/min. Two DSC runs were performed tocheck the reproducibility. No DSC anomalies were observed. Laboratory and synchrotronXRPD data were taken, and magnetic properties were measured for the sample after this DSCexperiment, and the transformation to AP-BiFe0.6Mn0.4O3 was confirmed.4. ConclusionsIn conclusion, two modifications of the BiFe0.6Mn0.4O3 perovskite were prepared: theHP modification was prepared by the direct high-pressure high-temperature method at6 GPa, and the AP modification was prepared with a “conversion polymorphism” strategy.The transformation of the HP modification to the AP modification was studied in situ, andcrystal structures of both modifications were investigated with synchrotron powder X-raydiffraction. The peculiar magnetic properties of HP-BiFe0.6Mn0.4O3 and AP-BiFe0.6Mn0.4O3were investigated and have been reported herein.Funding: This research received no external funding.Data Availability Statement: The raw data supporting the conclusions of this article will be madeavailable by the author on request.Acknowledgments: Synchrotron radiation was used at the powder diffraction beamline BL02B2 atSPring-8 with permission from the Japan Synchrotron Radiation Research Institute (Proposal Number:2021A1334). We thank S. Kobayashi for his help at BL02B2 of SPring-8. MANA was supported by theWorld Premier International Research Center Initiative (WPI), MEXT, Japan.Conflicts of Interest: The author declares no conflict of interest.References1. Tokura, Y.; Seki, S.; Nagaosa, N. Multiferroics of spin origin. Rep. Prog. Phys. 2014, 77, 076501. [CrossRef] [PubMed]2. Fiebig, M.; Lottermoser, T.; Meier, D.; Trassin, M. The evolution of multiferroics. Nature Rev. Mater. 2016, 1, 16046. [CrossRef]3. 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MDPI and/or the editor(s) disclaim responsibility for any injury topeople or property resulting from any ideas, methods, instructions or products referred to in the content.https://doi.org/10.1088/0953-8984/25/13/135902https://doi.org/10.1021/cm201774yhttps://doi.org/10.1063/1.3437396https://doi.org/10.3390/nano10040801https://doi.org/10.1021/cm9021084https://doi.org/10.1103/PhysRevB.79.214113https://doi.org/10.1016/j.jssc.2012.01.025https://doi.org/10.1039/C9CC00472Fhttps://www.ncbi.nlm.nih.gov/pubmed/30938726https://doi.org/10.1021/ic302384jhttps://www.ncbi.nlm.nih.gov/pubmed/23368634https://doi.org/10.1103/PhysRevB.82.100416https://doi.org/10.1021/cm1036925https://doi.org/10.1107/S0108768196012414https://doi.org/10.1107/S0108768198003802https://doi.org/10.1063/1.4752277https://doi.org/10.3390/nano12091565https://doi.org/10.3390/nano12162813https://www.ncbi.nlm.nih.gov/pubmed/36014678https://doi.org/10.1103/PhysRevB.83.184412https://doi.org/10.1063/1.5135586https://doi.org/10.1063/1.4999454https://www.ncbi.nlm.nih.gov/pubmed/28863664https://doi.org/10.4028/www.scientific.net/MSF.321-324.198 Introduction  Results and Discussion  Materials and Methods  Conclusions  References