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## Creator
[Alexei A. Belik](https://orcid.org/0000-0001-9031-2355)
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry Letters, copyright © 2024 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.chemmater.4c01720[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)
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[Hybrid Multiferroic Behavior in the Double Perovskite (Ca0.5Mn1.5)MnWO6](https://mdr.nims.go.jp/datasets/bb66e54f-b27d-4a92-847a-6119e9d51a02)
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Crystal structures of quadruple perovskites RMn3O6 (R = Gd, Er, and Tm) 1 Hybrid Multiferroic Behavior in the Double Perovskite (Ca0.5Mn1.5)MnWO6 Alexei A. Belik* Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan 2 Abstract Multiferroic materials with ordered electric dipoles and magnetic spins attract a lot of attention from viewpoints of applications and fundamental science. Multiferroics are generally classified into type-I, where (anti)ferroelectric and magnetic transitions are well separated and have completely different origins, and type-II, where magnetic structures break crystallographic inversion symmetry. Type-III multiferroics were recently introduced, which are close to type-I, but they do not show non-polar-to-polar structural transitions as polar structures are fixed by chemical order. In this work, we describe dielectric and magnetic behaviors observed in the double perovskites, (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6, crystallizing in space group P21/n. Dielectric constant of these compounds showed a peak at TC = 22 K and TC = 27 K, respectively, and followed the Curie-Weiss law in wide temperature ranges between TC and 300 K, where TC is an (anti)ferroelectric transition temperature – this behavior is typical for type-I multiferroics with proper (anti)ferroelectric transitions. At the same time, TC matches with the Néel temperature TN – this behavior is typical for type-II multiferroics. Therefore, materials with such behavior can be called hybrid multiferroics. 3 1. Introduction Materials that have ordered electric dipoles and magnetic spins are in general called multiferroics nowadays1–4 even though the term was originally introduced only for materials with simultaneous ferroelectric and ferromagnetic orders.5,6 A revision of the definition was “forced” by the discovery of spin-induced ferroelectric transitions in predominantly antiferromagnetic (AFM) materials.7 In other words, “anti” properties were added to the definition.4 After intensive studies, a general classification was introduced with type-I and type-II multiferroics. In type-I multiferroics, a ferroelectric transition occurs at a different temperature than a magnetic transition as they have completely different origins.1–3 Therefore, the coupling between magnetism and ferroelectricity is usually weak. In type-II multiferroics, a specific order of magnetic spins breaks a crystallographic center of symmetry, and weak spontaneous polarization may appear. Type-II multiferroics can show strong electromagnetic coupling. Temperature dependence of dielectric constant in type-I multiferroics depends on the nature of a ferroelectric transition, whether it is proper (e.g., BiFeO3) or improper (e.g., YMnO3). And in proper (anti)ferroelectrics, dielectric constant usually follows the Curie-Weiss law above the (anti)ferroelectric Curie temperature (TC) in a wide temperature range.8 Dielectric constant peaks at TC (sometimes with very large values) and then decreases with decreasing temperature. There are examples of materials in which dielectric constant increases with decreasing temperature down to lowest temperatures, for example, in the so-called incipient or quantum ferroelectrics, such as SrTiO3 and related materials.9,10 In type-II multiferroics, dielectric constant usually slightly decreases with decreasing temperature (or nearly temperature independent), and spin-induced ferroelectric transitions appear as peaks/perturbations on such “background” dielectric curves. A new term – type-III multiferroics – was recently introduced to emphasize materials that are always polar.11,12 In other words, polar structures are fixed by chemical orders in them and, therefore, they do not show temperature-driven ferroelectric (or non-polar-to-polar structural) transitions. In many cases, they are not ferroelectric (as polarization cannot be switched by an external electric field), but they are pyroelectric. Magnetic behavior of type-I multiferroics below TC and behavior of type-III multiferroics should, 4 in principle, be the same as crystal structures are polar in both cases. We also note that near magnetic transition temperatures, which are usually much lower than TC, electric polarization of type-I multiferroics can also be unswitchable (similar to proposed type-III multiferroics), and ferroelectric switching is rarely demonstrated in type-II multiferroics, where pyroelectric current measurements are often used to support the appearance of spin-induced spontaneous polarization. In this work, we investigated dielectric and magnetic properties of the double perovskites, (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6, which crystallize in space group P21/n. Dielectric constant of these compounds increased with decreasing temperature and followed the Curie-Weiss law (with a negative Curie-Weiss temperature) from 300 K down to TC = 22 K ((Ca0.5Mn1.5)MnWO6) and TC = 27 K ((Ca0.3Mn1.7)MnWO6); this behavior is typical for proper ferroelectric or antiferroelectric transitions. At TC, characteristic peaks were observed on dielectric constant. At the same time, TC matches with the Néel temperature TN that is typical for type-II multiferroics. We suggest calling materials with such behavior as hybrid multiferroics. 2. Experimental Section (Ca2−xMnx)MnWO6 samples with x = 1, 1.5, 1.7, 1.75, 1.9, and 2 were prepared from stoichiometric mixtures of CaWO4, MnO (99.9 %), and WO3 (99.9 %), and a sample with x = 0 was prepared from a stoichiometric mixture of Ca3WO6, CaWO4, MnO (99.9 %). The synthesis was performed at about 6 GPa and about 1550 K for 2 h in Au capsules (for x = 0, 1, 1.5, 1.7, and 1.75) and about 1850 K for 1 h in Pt capsules (for x = 1, 1.75, 1.9, and 2) using a belt-type high-pressure instrument. After annealing at 1550 K or 1850 K, the samples were cooled down to room temperature by turning off the heating current, and the pressure was slowly released. Hard pellets of approximate diameter of 5 mm were recovered after opening capsules. Single-phase CaWO4 and Ca3WO6 were prepared from stoichiometric mixtures of WO3 and CaCO3 (99.99 %) by annealing in air at 1430 K for 60 h with several intermediate grindings. X-ray powder diffraction (XRPD) data were collected at room temperature on a RIGAKU MiniFlex600 diffractometer using CuKα radiation (2θ range of 8−100°, a step width of 0.02°, and scan speed of 2 °/min). Synchrotron XRPD data were collected at 5 room temperature on the beamline BL02B213 of SPring-8 (the intensity data were taken between 1.95° and 78.09° at 0.006° intervals in 2θ using a wavelength of λ = 0.619743 Å). The sample was placed into an open Lindemann glass capillary tube (inner diameter: 0.2 mm), which was rotated during measurements. The Rietveld analysis of all XRPD data was performed using the RIETAN-2000 program.14 Magnetic measurements were performed on a SQUID magnetometer (Quantum Design, MPMS3) between 2 and 300 K in an applied field of 10 kOe under both zero-field-cooled (ZFC) and field-cooled on cooling (FCC) conditions. Isothermal magnetization measurements were performed between −70 and 70 kOe at T = 5 K. Specific heat, Cp, at magnetic fields of 0 Oe and 90 kOe was recorded between 2 and 100 K on cooling by a pulse relaxation method using a commercial calorimeter (Quantum Design PPMS). Dielectric properties were measured using a NOVOCONTROL Alpha-A High Performance Frequency Analyzer between 3 K and 300 K on cooling and heating in a frequency range of 301 Hz and 73.7 kHz and at H = 0 Oe. Silver paste was used as electrodes. 3. Results and Discussion Structural analysis showed that (Ca0.5Mn1.5)MnWO6 crystallized in space group P21/n (a = 5.31951(2) Å, b = 5.49798(2) Å, c = 7.75735(3) Å, and β = 90.0315(7)°) with a full rock-salt-type ordering of Mn2+ and W6+ at the B sites. The refined occupation factors were g(Mn) = 1.002(4) and g(W) = 0.995(3). Ca2+ and Mn2+ cations are statistically disordered in one A site. Figure 1 shows Rietveld-refinement fits based on room-temperature synchrotron X-ray powder diffraction. The sample contained a small amount of CaWO4 impurity (about 0.7 wt. %). Refined structural parameters and main bond lengths are summarized in Tables 1 and 2. Bond-valence sum (BVS)15 values agreed with the expected formal oxidation states. The crystal structure of (Ca0.5Mn1.5)MnWO6 is illustrated on Figure 2. A sample with the composition of (Ca0.3Mn1.7)MnWO6 also crystallized in space group P21/n with a = 5.30061(4) Å, b = 5.48014(5) Å, c = 7.75372(6) Å, and β = 90.0605(12)°. On the other hand, the x = 1.75 sample, prepared at 1550 K, already 6 contained about 15 weight % of a phase with a structure of the high-pressure modification of Mn3WO616 and with broadened reflections for a Mn3WO6-type phase (plus the sample had a small amount of MnWO4 impurity). The amount of the Mn3WO6 phase remained almost the same (about 20 wt. %, but with sharper reflections) after the synthesis of the x = 1.75 sample at 1850 K (plus the sample had a small amount (about 2 wt. %) of MnWO4 impurity). Therefore, the (Ca2−xMnx)MnWO6 solid solutions are formed up to about x = 1.7 independent of the annealing temperature. The x = 1.9 and 2 samples crystallized in the Mn3WO6-type structure with small amounts (about 2 wt. %) of MnWO4 impurity. The formation of MnWO4 impurity was also observed in the previous work.16 The x =1 sample was prepared in the P42/n modification at 1550 K, and in the P21/n modification at 1850 K in agreement with the previous work;17 both modifications contained small amounts of CaWO4 impurity; in addition, the P21/n modification contained a small amount of an admixture of the P42/n modification and wise versa. Figure 1. Experimental (black crosses), calculated (red line), and difference (blue line at the bottom) synchrotron X-ray powder diffraction patterns of (Ca0.5Mn1.5)MnWO6 at T = 297 K between 5° and 40°. The tick marks show possible Bragg reflection -0.10.00.10.20.30.40.50.65 15 25 35-0.020.020.060.100.147 10 13 16 19Intensity (counts/106 ) 2θ (deg): λ = 0.61974 Å 7 positions for the main phase, CaWO4 impurity, and Au (a contamination from a capsule material) from top to bottom. Inset shows a zoomed part between 7° and 19.7°. Figure 2. The crystal structure of (Ca0.5Mn1.5)MnWO6 viewed along the b axis. Table 1. Refined structural parameters of (Ca0.5Mn1.5)MnWO6 at room temperature from synchrotron powder X-ray diffraction data a Site Wyck. x y z Biso. (Å2) Mn 2c 0.5 0.0 0.5 0.71(2) W 2d 0.5 0.0 0.0 0.568(8) Ca/Mn 4e 0.9932(7) 0.0493(2) 0.2466(2) 1.06(3) O1 4e 0.3850(9) 0.9435(10) 0.2301(9) 0.86(14) O2 4e 0.1598(12) 0.2095(12) 0.5697(11) 1.80(19) O3 4e 0.7010(12) 0.3284(11) 0.4474(10) 1.11(15) 8 a. Space group P21/n (No. 14, cell choice 2), Z = 2. Wavelength: λ = 0.61974 Å. Occupation factors of the Mn, W, O1, O2, and O3 sites are unity (g = 1); the occupation factor of the Ca/Mn site is 0.25Ca + 0.75Mn. Wyck.: Wyckoff position. a = 5.31951(2) Å, b = 5.49798(2) Å, c = 7.75735(3) Å, β = 90.0315(7)o, and V = 226.8756(13)Å3; ρ = 6.400 g/cm3; Rwp= 7.39 %, Rp= 5.41 %, RB = 3.68 %, and RF = 2.83 %. Impurities: CaWO4 (0.7 wt. %) and Au (0.5 wt. %; a contamination from a capsule material). Table 2. Bond lengths (in Å), bond angles (in deg), and bond-valence sum (BVS) in (Ca0.5Mn1.5)MnWO6 at room temperature from synchrotron powder X-ray diffraction data. Ca/Mn−O1 2.168(6) Mn−O1 ×2 2.203(7) Ca/Mn−O2 2.172(8) Mn−O2 ×2 2.213(6) Ca/Mn−O3 2.192(8) Mn−O3 ×2 2.138(7) Ca/Mn−O1 2.269(6) BVS(Mn2+) +2.08 Ca/Mn−O2 2.605(7) W−O1 ×2 1.913(7) Ca/Mn−O3 2.658(7) W−O2 ×2 1.888(7) Ca/Mn−O3 2.683(7) W−O3 ×2 1.894(6) Ca/Mn−O2 2.800(8) BVS(W6+) +6.39 BVS(Ca/Mn2+) +1.90 Mn−O1−W ×2 140.84(8) Mn−O2−W ×2 137.61(8) Mn−O3−W ×2 143.11(8) BVS = ∑=Nii1ν , νi = exp[(R0 − li)/B], N is the coordination number, li is a bond length, B = 0.37, R0(Mn2+) = 1.79, R0(W6+) = 1.921, R0(Ca2+) = 1.967, and R0(Ca/Mn2+) = 1.834 (an average of 0.25Ca2+ and 0.75Mn2+).15 9 Figure 3. Temperature dependence of dielectric constant of (a) (Ca0.5Mn1.5)MnWO6 575859600 50 100 150301 Hz 903 Hz2.71 kHz 8.16 kHz24.5 kHz 73.7 kHz78838893981031080 50 100 150301 Hz903 Hz2.71 kHz8.16 kHz24.5 kHz73.7 kHzfit7173757779810 50 100 150301 Hz903 Hz2.71 kHz8.16 kHz24.5 kHz73.7 kHzfitDielectric constant Temperature (K) TC = TN = 22 K ε0 = 64.9(7) C = 2065(31) K θ = −128(2) K @ 73.7 kHz T = 40−180 K Dielectric constant @ 73.7 kHz T = 27−180 K ε0 = 60.35(4) C = 5675(17) K θ = −119.2(3) K (b) (Ca0.3Mn1.7)MnWO6 (a) (Ca0.5Mn1.5)MnWO6 TC = TN = 27 K Dielectric constant Ca2MnWO6 Ca2CaWO6 TN = 16 K (c) 10 and (b) (Ca0.3Mn1.7)MnWO6 between T = 3 K and 180 K at different frequencies (f) from 301 Hz to 73.7 kHz at zero magnetic field. The black line shows a fit by the Curie-Weiss law (eq. (1)), where the calculated curve was extended down to 3 K; the fitting parameters are given on the figure. TN: Néel temperature, TC: (anti)ferroelectric Curie temperature. (c) Temperature dependence of dielectric constant of Ca2MnWO6 and Ca2CaWO6 (only at 301 Hz and 903 Hz for clarity) between T = 3 K and 180 K. Temperature dependence of dielectric constant of (Ca0.5Mn1.5)MnWO6 is shown on Figure 3a. There was almost no frequency dependence between 3 K and 180 K, and dielectric constant increased with deceasing temperature down to TC = 22 K. At TC, a sharp peak was observed typical for a ferroelectric or antiferroelectric transition. Ferroelectric transitions are usually accompanied by peaks on dielectric loss, while antiferroelectric transitions do not show anomalies on dielectric loss.9,18 No anomalies were observed on dielectric loss in (Ca0.5Mn1.5)MnWO6 (Figure S1) suggesting an antiferroelectric transition. Dielectric constant could be fit with the Curie-Weiss law above TC in a temperature range of 27–180 K: ε(T) = ε0 + C/(T−θ) (1). The fitting parameters were ε0 = 64.9(7), C = 2065(31) K, and θ = −128(2) K (Figure 3a). A negative Curie-Weiss temperature was obtained again pointing to an antiferroelectric transition. Above about 200 K, an upturn of dielectric constant was observed at low frequencies due to increased conductivity and Maxwell-Wagner contributions. However, dielectric constant continued to follow the Curie-Weiss law up to 300 K at high frequencies (Figure S2). 11 Figure 4. Magnetic properties of (a) (Ca0.5Mn1.5)MnWO6 and (b) (Ca0.3Mn1.7)MnWO6. The left-hand axis shows a field-cooled on cooling (FCC) dc magnetic susceptibility (χ = M/H) curve measured at H = 10 kOe. Right-hand axis shows the χ−1 versus T curve with the Curie-Weiss fit (black line). The parameters of the fit are shown on the figure. Magnetic properties are reported on Figure 4a. M versus H curves at 5 K showed linear behavior without any detectable hysteresis suggesting pure AFM properties (Figure 0.020.030.040.050 50 100 150 200 250 300010203040FCC, 10 kOe0.020.030.040.050 50 100 150 200 250 300010203040FCC, 10 kOeχ (emu×mol−1×Oe−1) Temperature (K) χ− 1 (emu− 1×mol×Oe) µeff = 9.66(2)µB θ = −209(2) K µcalc = 9.354µB TN = 22 K µeff = 9.81(2)µB θ = −215(2) K µcalc = 9.721µB χ (emu×mol−1×Oe−1) χ−1 (emu−1×mol×Oe) (b) (Ca0.3Mn1.7)MnWO6 (a) (Ca0.5Mn1.5)MnWO6 TN = 27 K 12 S4). Temperature-dependent magnetic susceptibility showed a small peak at TN = 22 K. At high temperatures, inverse magnetic susceptibilities followed the Curie-Weiss law: χ−1(T) = 8(T−θ)/µeff2 (2). The experimental effective magnetic moment (µeff) of 9.66µB was close to the calculated value of 9.35µB, and a negative Curie-Weiss temperature (θ) confirmed predominant AFM interactions. Specific heat measurements (Figure 5) showed a clear peak near 22 K confirming a long-range magnetic ordering. 13 Figure 5. (a) Specific heat data (Cp/T versus T) for (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6 at H = 0 Oe and 90 kOe. (b) (Left-hand axis) Cp versus T curves for (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6 at H = 0 Oe. (Right-hand axis) Excess entropy in (Ca0.3Mn1.7)MnWO6 in comparison with (Ca0.5Mn1.5)MnWO6 at H = 0 Oe. 010203040500 10 20 30 40 50 6001230.00.51.01.50 20 40 60 80 1000 Oe, cooling90 kOe, cooling0 Oe, cooling90 kOe, coolingCp / T (J K−2 mol−1) Temperature (K) x = 1.5 T N = 22 K x = 1.7 TN = 27 K x = 1.5 x = 1.7 Temperature (K) Cp (J K−1 mol−1) Sexcess (J K−1 mol −1) (a) (b) 14 Therefore, magnetic and specific heat data prove that an AFM long-range magnetic transition takes place at the Néel temperature TN = 22 K. At the same temperature, a clear dielectric constant peak was observed. This is what is usually observed in type-II multiferroics. A sample with the composition of (Ca0.3Mn1.7)MnWO6 was also investigated, and similar dielectric, magnetic, and specific heat anomalies were observed only at a higher temperature of TN = TC = 27 K (Figures 3b, 4b, and 5 and Figures S1, S3, and S4). The fit by eq. (1) gave ε0 = 60.35(4), C = 5675(17) K, and θ = −119.2(3) K. Shifts of both TN and TC in (Ca0.3Mn1.7)MnWO6 give additional evidence that the transitions take place at the same temperature point. Specific heat of the x = 1.5 and 1.7 samples almost matched each other in temperature ranges of 2–22 K and above about 50 K. The excess entropy of the x = 1.7 sample in comparison with the x = 1.5 sample was calculated to be about 3.4 J×mol−1×K−1 (Figure 5b), which can approximately be explained by a larger amount of magnetic Mn2+ cations (0.2×R×ln(2S+1) ≈ 3.0 J×mol−1×K−1, where R is the gas constant and S = 5/2 is spin). On the other hand, isostructural Ca2MnWO619,20 (space group P21/n, a = 5.4564(1) Å, b = 5.6471(1) Å, c = 7.8010(1) Å, and β = 90.202(2)°) showed nearly frequency independent dielectric constant between 2 K and 230 K (Figure 3c and Figure S5), where dielectric constant only very slightly decreased with decreasing temperature without any Curie-Weiss behavior. A very weak kink (not a peak) was observed on dielectric constant at TN = 16 K; the kink could originate from magnetostriction and magnetodielectric effects.4 Our specific heat and magnetic measurements of Ca2MnWO6 (Figures S6 and S7) confirmed an AFM long-range ordering. Therefore, dielectric properties of isostructural (Ca2−xMnx)MnWO6 compounds with x = 0 and x = 1.5 (x = 1.7), having long-range AFM orderings, were quite different. We also investigated dielectric properties of another isostructural compound without magnetic ions, Ca2CaWO621 (Figure 3c), where dielectric constant was frequency independent between 3 K and 330 K (not shown) and very slightly decreased with decreasing temperature as expected. We note that no dielectric loss anomalies were observed in Ca2MnWO6 (Figure S5) and Ca2CaWO6. 15 Table 3. Néel temperatures (TN) and Parameters of the Curie-Weiss Fit for (Ca2−xMnx)MnWO6 x TN (K) µeff (µB/f.u.) µcalc (µB/f.u.) θ (K) FI 0 16 5.886(12) 5.916 −61.5(1.3) 3.8 1 8a) 8.43(2) 8.367 −158(2) 18a) 1.5 22 9.66(2) 9.354 −209(2) 9.5 1.7 27 9.81(2) 9.721 −215(2) 8.0 The Curie-Weiss fits were performed between 200 and 300 K using the FCC χ −1 versus T data at 10 kOe. FI: Frustration index = θ/TN. a) from Ref. 17, 8 K is a spin-glass temperature. Previous magnetic measurements and neutron diffraction studies of Ca2MnWO6 (x = 0) showed that there is an AFM long-range ordering at TN = 16 K with the propagation vector of (0, ½, ½).19,20 The experimental ordered magnetic moment of 4.9µB at 1.9 K nearly reached the full expected value of 5µB.19 Despite the full ordered moment and a simple AFM structure Ca2MnWO6 has a moderate frustration index (defined as θ/TN) of about 3.8 (Table 3). Ca2MnWO6 has only super-super-exchange interactions, Mn–O–(W)–O–Mn, and fully ordered double perovskites with one non-magnetic B cation (and non-magnetic A cations) form a frustrated square-lattice model in general.22 The frustration index increased in the x = 1.5 and 1.7 samples to about 8–10. On the other hand, magnetic measurements and neutron diffraction studies of (CaMn)MnWO6 (x = 1) showed the absence of long-range magnetic ordering.17 This fact shows that the introduction of magnetic Mn2+ cations into the A sites enhances spin frustration until some critical concentrations of Mn2+ cations. Our specific heat measurements of (CaMn)MnWO6 (Figure S8) confirmed the absence of a long-range magnetic ordering. Dielectric measurements of CaMnMnWO6 (Figure S9) showed nearly frequency- and temperature-independent properties without any Curie-Weiss behavior. Therefore, dielectric properties of isostructural (Ca2−xMnx)MnWO6 compounds with x = 1 (without long-range magnetic ordering) and x = 1.5 and 1.7 (with long-range magnetic ordering) were quite different. Higher concentrations of magnetic and small Mn2+ cations 16 at the A site in the x = 1.5 and 1.7 samples could stabilize a new magnetic structure (which yet to be determined in future studies) and result in different behavior. We note that magnetodielectric effects at AFM ordering transitions with similar (Curie-Weiss-like) dependence of dielectric constant were observed in the literature and explained by spin-phonon coupling without development of ferroelectric order.4,10,23–27 In case of BiMn3Cr4O12, it was suggested originally that TC ≠ TN;26 however, it was showed later that TC = TN.27 Explanations provided in the literature do not probably exclude the development of antiferroelectric order (non-polar),4,10 and spin-phonon coupling cannot explain the Curie-Weiss behavior of dielectric constant far above TN as observed in (Ca2−xMnx)MnWO6 with x = 1.5 and 1.7 and quite different dielectric behavior of isostructural (Ca2−xMnx)MnWO6 as a function of the composition. The evolution of dielectric and magnetic properties in (Ca2−xMnx)MnWO6 as a function of x is interesting and deserves further studies. 4. Conclusion In conclusion, double perovskites (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6 were prepared by a high-pressure high-temperature method. Their dielectric constant showed a characteristic peak at TC = 22 K and TC = 27 K, respectively, and followed the Curie-Weiss law in wide temperature ranges above TC up to 300 K that is typical for type-I multiferroics with proper ferroelectric (or antiferroelectric) transitions. On the other hand, TC matched with TN that is typical for type-II multiferroics. Therefore, we suggest that (Ca0.5Mn1.5)MnWO6 and (Ca0.3Mn1.7)MnWO6 are examples of materials that can be called hybrid multiferroic materials bearing features of type-I and type-II multiferroics. Author Information Corresponding Author Alexei.Belik@nims.go.jp Notes The authors declare no competing financial interest. 17 Associated Content Supporting Information The Supporting information is available free of charge at …. Figures with detailed dielectric and magnetic properties of (Ca0.5Mn1.5)MnWO6, (Ca0.3Mn1.7)MnWO6, and Ca2MnWO6 (PDF). Acknowledgements This work was partially supported by a Grant-in-Aid for Scientific Research (No. JP22H04601) from the Japan Society for the Promotion of Science and the Kazuchika Okura Memorial Foundation (No. 2022-11). Synchrotron radiation was used at the powder diffraction beamline BL02B2 at SPring-8, with permission from the Japan Synchrotron Radiation Research Institute (Proposal Number: 2023B1676). We thank Dr. S. Kobayashi for his help at BL02B2 of SPring-8. MANA is supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan. 18 References (1) Tokura, Y.; Seki, S.; Nagaosa, N. Multiferroics of Spin Origin. 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