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Yuichi Mori, Soga Nakatsuka, Masaaki Doi, Toshiyuki Shima

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[Creative Commons BY Attribution 4.0 International](https://creativecommons.org/licenses/by/4.0/)

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[Enhancement of thermal stability of Sm(Fe-Co)12-B thin films by cap layer deposition and post-annealing](https://mdr.nims.go.jp/datasets/79e22585-20ea-4802-a45c-3f652b6f60a3)

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REPM2025、スライド(7)revEnhancement of thermal stability of Sm(Fe-Co)12-B        thin films by cap layer deposition and post-annealingThe 28th International Workshop on Rare Earth and Future Permanent Magnets and Their Applications July 31, 2025Tsukuba International Congress CenterY. Mori, S. Nakatsuka, M. Doi, and T. ShimaGraduate School of Engineering, Tohoku Gakuin UniversitySendai, JapanAcknowledgment: Dr. H. Sepehri Amin, Dr. A. Bolyachkin, Dr. Y. K. Takahashi, Dr. K. Hono (NIMS) Introduction: Sm-Fe based compounds and stabilizing elementsabc: R: Fe (8j): Fe (8i): Fe (8f)ThMn12-type crystal structureTypical Sm-Fe-based compoundsChemical composition SmFe5 Sm2Fe17 SmFe12Crystalstructure CaCu5-type Th2Zn17-type ThMn12-typeFe content(at.%) 83.3 89.5 92.3Phase stability Unstable Stable UnstableS. Saito et al., J. Alloys Compd., 929 (2022) 167280.Elements Atomic radius (nm) Substitution siteTi 0.147 8iV 0.134 8iCr 0.128 8i, 8j, 8fMo 0.139 8iAl 0.143 8j, 8fSi 0.132 8j, 8fMn 0.127 8i, 8j, 8fW 0.139Zr 0.16 2aCo 0.125 8j, 8fNb 0.146 8iTa 0.146 8iRe 0.137Fe 0.126 -Sm 0.18 -Y. K. Takahashi et al., Sci. Technol. Adv. Mater., 22(1) (2021) 449-460.Phase stabilizing elements of SmFe121RFe12 compounds: Candidate for next generation permanent magnetµ0Ms vs µ0HA for various RFe12 compounds• µ0Ms and µ0HA superior than Nd2Fe14Bmagnets were realized in Sm(Fe-Co)12compounds.16141210864202.22.01.81.61.41.21.0★Sm(Fe1-xCox)12x = 0.1 x = 0.2(Sm1-xZrx)(Fe0.8Co0.2)12x = 0.18x = 0.26SmFe12NdFe12NxNd2Fe14BSm(Fe1-xCox)12TiSmFe11TiNdFe11TiN(Sm0.8Zr0.2)(Fe,Co)11.5Ti0.5YFe11TiNAnisotropy field, µ0HA (T)Saturation magnetization, µ0Ms (T)Next generation magnetsµ0Ms-T for various magnetic materialsY. Hirayama et al., Scr. Mater., 138 (2017) 62-65.• Partial substitution of Fe with Coincreases the TC of SmFe12.P. Tozman et al., Scr. Mater., 194 (2021) 113686.2Effect of B addition for Sm(Fe-Co)12 thin filmsBF-TEM and EDS mapsµ0H (T) µ0H (T)-2.0-1.00.01.02.0-4 -2 0 2 4IPOOP-2.0-1.00.01.02.0-4 -2 0 2 4IPOOPµ 0M (T)µ 0M (T)M-H curvesRef: H. Sepehri-Amin et al., Scr. Mater., 242 (2024) 115955.,    M. Kambayashi et al., J. Magn. Soc. Jpn., 45 (2021) 66-69.µ0Hc = 0.1 T• No clear grainboundary phasewas formed• Uniform distributionof Sm, Fe, and CoSm(Fe-Co)12BF-TEM and EDS mapsSm(Fe-Co)12-Bµ0H (T) µ0H (T)-2.0-1.00.01.02.0-4 -2 0 2 4IPOOP-2.0-1.00.01.02.0-4 -2 0 2 4IPOOPµ 0M (T)µ 0M (T)M-H curvesµ0Hc = 1.1 T• Well defined grainboundary phase• Columnar structurewas formed• Coercivity increased3Al cap layer diffusion into GB phase in Sm(Fe-Co)12-B thin films4Ref: H. Sepehri-Amin et al., Scr. Mater., 242 (2024) 115955.,    M. Kambayashi et al., J. Magn. Soc. Jpn., 45 (2021) 66-69.-1.0-0.50.00.51.0-4 -2 0 2 4IPOOPM/Msµ0H (T)-2.0-1.00.01.02.0-4 -2 0 2 4IPOOPµ 0M (T)µ0H (T)µ0Hc = 1.8 T• Al marked withyellow was diffuseddown into GB phaseM-H curvesBF-TEM and EDS mapsSm(Fe-Co)12-B/Al + post annealingBF-TEM and EDS mapsSm(Fe-Co)12-Bµ0H (T) µ0H (T)-2.0-1.00.01.02.0-4 -2 0 2 4IPOOP-2.0-1.00.01.02.0-4 -2 0 2 4IPOOPµ 0M (T)µ 0M (T)M-H curvesµ0Hc = 1.1 T• Well defined grainboundary phase• Columnar structurewas formed• Coercivity increasedCap layer deposition and post annealing is important to control microstructureObjectiveSample preparation• UHV magnetron sputtering system • Substrate : MgO (100) single crystal• Targets : Sm, Fe, Fe50Co50, Fe80B20, V• Sub. temp. : Ts = 400 ºC• Buffer layer : V (20 nm)• Main layer : Sm(Fe-Co)12-B (100 nm)• Cap layer : Zr, Nb (10 nm)• Ann. temp. : Ta = 400 ~ 650 ºC• Ann. time : 1 hour• Cover layer : V (10 nm) depo@R.T.V (20 nm)MgO sub.Sm(Fe-Co)12-B(100 nm)Nb or Zr (10 nm)Thin film structureV (10 nm)In this study, in order to control the structure and improve the magnetic properties,stabilizing element such as Nb and Zr was selected as a capping layer materialand post-annealed for the Sm(Fe-Co)12-B thin film.Characteristic measurement• Crystal structure : XRD• Magnetic properties : SQUIDExperimental procedure5Intensity (log. scale) 807060504030202 theta (deg.) -2.0-1.00.01.02.0⊥://:(a) w/o ann.(b) Ta = 400 ºCKu = 4.59 MJ/m3 µ0Ms = 1.35 Tµ0Hc = 1.19 TMr/Ms = 82.1 % 1.64 T 0.08 T 10.6 %µ0HA = 12 TMagnetization (T)(a) w/o ann. 1.64 T 0.07 T 12.1 % 1.61 T 0.09 T 15.4 % -1.10 MJ/m3  -1.04 MJ/m3 Out-of-plane Main-phase (1-12)α-Fe, α-FeCoMgO (200)V (200) (004)(002)-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 4 5.44 MJ/m3  4.78 MJ/m3  1.44 T 1.10 T 88.3 %(b) Ta = 400 ºC 1.50 T 1.10 T 81.0 %(c) 500 ºC(e) 625 ºC(f) 650 ºCMagnetic field (T)(d) 600 ºC  -0.83 MJ/m3 (c) 500 ºC(d) 600 ºC(e) 625 ºC(f) 650 ºCIntensity (log. scale) 807060504030202 theta (deg.) -2.0-1.00.01.02.0⊥://:(a) w/o ann.(d) 600(e) 625(f) 650(b) Ta = 400 ºC(c) 500Ku = 4.59 MJ/m3 µ0Ms = 1.35 Tµ0Hc = 1.19 TMr/Ms = 82.1 % 1.64 T 0.08 T 10.6 %µ0HA = 12 TMagnetization (T)(a) w/o ann. 1.64 T 0.07 T 12.1 % 1.61 T 0.09 T 15.4 % -1.10 MJ/m3  -1.04 MJ/m3 Out-of-plane Main-phase (1-12)α-Fe, α-FeCoMgO (200)V (200) (004)(002)-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 4 5.44 MJ/m3  4.78 MJ/m3  1.44 T 1.10 T 88.3 %(b) Ta = 400 ºC 1.50 T 1.10 T 81.0 %(c) 500 ºC(e) 625 ºC(f) 650 ºCMagnetic field (T)(d) 600 ºC  -0.83 MJ/m3 1)  Sm(Fe-Co)12-B thin films with different TaTa = 400 ~ 600ºC (1 h)MgO sub./ V (20 nm)/ Sm(Fe-Co)12-B (100 nm)/ V (10 nm) 6Intensity (log. scale) 807060504030202 theta (deg.) µ0Ms = 1.50 Tµ0Hc = 0.98 TMr/Ms = 82.0 % 1.33 T 0.47 T 66.9 %Magnetization (T) 3.68 MJ/m3 Main-phase (1-12)1-51-3α-Fe, α-FeCoZrB2MgO (200)V (200)(004)(b) Ta = 400 ºC  3.98 MJ/m3  1.60 MJ/m3 µ0HA = 12 T(a) w/o ann. Ku = 4.81 MJ/m3  3.38 MJ/m3  1.45 T 0.87 T 75.5 % 1.16 T 0.32 T 50.5 % 1.39 T 0.74 T 82.6 % 1.97 MJ/m3  1.13 T 0.30 T 50.8 %Out-of-plane(b) Ta = 400 ºC(002) (a) w/o ann.(c) 500 ºC(d) 600 ºC(e) 625 ºC(f) 650 ºCMagnetic field (T)-2.0-1.00.01.02.0  (c) 500 ºC(e) 625 ºC(f) 650 ºC(d) 600 ºC-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 4Intensity (log. scale) 807060504030202 theta (deg.) µ0Ms = 1.50 Tµ0Hc = 0.98 TMr/Ms = 82.0 % 1.33 T 0.47 T 66.9 %Magnetization (T) 3.68 MJ/m3 Main-phase (1-12)1-51-3α-Fe, α-FeCoZrB2MgO (200)V (200)(004)(b) Ta = 400 ºC  3.98 MJ/m3  1.60 MJ/m3 µ0HA = 12 T(a) w/o ann. Ku = 4.81 MJ/m3  3.38 MJ/m3  1.45 T 0.87 T 75.5 % 1.16 T 0.32 T 50.5 % 1.39 T 0.74 T 82.6 % 1.97 MJ/m3  1.13 T 0.30 T 50.8 %Out-of-plane(b) Ta = 400 ºC(002) (a) w/o ann.(c) 500(d) 600(e) 625(f) 650Magnetic field (T)-2.0-1.00.01.02.0  (c) 500 ºC(e) 625 ºC(f) 650 ºC(d) 600 ºC-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 42)  Sm(Fe-Co)12-B/Zr thin films with different TaMgO sub./ V (20 nm)/ Sm(Fe-Co)12-B (100 nm)/ Zr (10 nm)/ V (10 nm) 7Ta = 400 ~ 600ºC (1 h)Out-of-planeIntensity (log. scale) 807060504030202 theta (deg.) (002) 3.22 MJ/m3  4.45 MJ/m3  1.26 T 0.64 T 81.0 %Ku = 5.31 MJ/m3 µ0Ms = 1.54 Tµ0Hc = 1.08 TMr/Ms = 79.0 % 1.41 T 0.96 T 86.9 % 4.49 MJ/m3  1.41 T 1.12 T 85.1 % 5.37 MJ/m3  5.83 MJ/m3 Magnetization (T)::µ0HA = 12 T(a) w/o ann.(d) 600 ºC(e) 625 ºC(f) 650 ºC(b) Ta = 400 ºC(c) 500 ºC MgO (200)V (200) (004)Main-phase (1-12)1-5α-Fe, α-FeCo Nb3B2Magnetic field (T) 1.32 T 0.39 T 58.8 % 1.39 T 1.10 T 88.0 %-2.0-1.00.01.02.0 (b) Ta = 400 ºC(c) 500 ºC(e) 625 ºC(f) 650 ºC(d) 600 ºC(a) w/o ann.-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 4Out-of-planeIntensity (log. scale) 807060504030202 theta (deg.) (002) 3.22 MJ/m3  4.45 MJ/m3  1.26 T 0.64 T 81.0 %Ku = 5.31 MJ/m3 µ0Ms = 1.54 Tµ0Hc = 1.08 TMr/Ms = 79.0 % 1.41 T 0.96 T 86.9 % 4.49 MJ/m3  1.41 T 1.12 T 85.1 % 5.37 MJ/m3  5.83 MJ/m3 Magnetization (T)::µ0HA = 12 T(a) w/o ann.(d) 600(e) 625(f) 650(b) Ta = 400 ºC(c) 500 MgO (200)V (200) (004)Main-phase (1-12)1-5α-Fe, α-FeCo Nb3B2Magnetic field (T) 1.32 T 0.39 T 58.8 % 1.39 T 1.10 T 88.0 %-2.0-1.00.01.02.0 (b) Ta = 400 ºC(c) 500 ºC(e) 625 ºC(f) 650 ºC(d) 600 ºC(a) w/o ann.-2.0-1.00.01.02.0-2.0-1.00.01.02.0-4 -2 0 2 4 -4 -2 0 2 43)  Sm(Fe-Co)12-B/Nb thin films with different TaMgO sub./ V (20 nm)/ Sm(Fe-Co)12-B (100 nm)/ Nb (10 nm)/ V (10 nm) 8Ta = 400 ~ 600ºC (1 h)M-H curves for Sm(Fe-Co)12-B, Sm(Fe-Co)12-B/Zr, and Sm(Fe-Co)12-B/Nb thin films -4 -2 0 2 4-4 -2 0 2 4-4 -2 0 2 4 -4 -2 0 2 4-1.04 MJ/m3 0.08 T 4.78 MJ/m3 1.10 T 5.44 MJ/m3 1.10 T(c) 500 ºC (f) 650 ºC-1.10 MJ/m3 0.07 T-4 -2 0 2 4-2.0-1.00.01.02.0-4 -2 0 2 4⊥//Ku = 4.59 MJ/m3µ0Hc = 1.19 T(d) 600 ºC(a) w/o ann. (b) Ta = 400 ºC (e) 625 ºC -0.83 MJ/m3 0.09 Tµ 0M (T)-2.0-1.00.01.02.0-4 -2 0 2 4⊥//-4 -2 0 2 4Ku = 4.81 MJ/m3µ0Hc = 0.98 T-4 -2 0 2 4(c) 500 ºC-4 -2 0 2 4 3.38 MJ/m3 0.47 T-4 -2 0 2 4-4 -2 0 2 4(b) Ta = 400 ºC (e) 625 ºC(a) w/o ann. (d) 600 ºC 3.98 MJ/m3 0.87 T 1.60 MJ/m3 0.32 T 3.68 MJ/m3 0.74 T(f) 650 ºC 1.97 MJ/m3 0.30 Tµ 0M (T)-4 -2 0 2 4-4 -2 0 2 4-4 -2 0 2 4 4.49 MJ/m3 0.96 T-4 -2 0 2 4 -4 -2 0 2 4-2.0-1.00.01.02.0-4 -2 0 2 4⊥//Ku = 5.31 MJ/m3µ0Hc = 1.08 T(a) w/o ann. (d) 600 ºC 4.45 MJ/m3 0.64 T 5.37 MJ/m3 1.12 T(b) Ta = 400 ºC (c) 500 ºC (e) 625 ºC (f) 650 ºC 3.22 MJ/m3 0.39 T 5.83 MJ/m3 1.10 Tµ 0M (T)µ0H (T)1) Sm(Fe-Co)12-B3) Sm(Fe-Co)12-B/ Nb2) Sm(Fe-Co)12-B/ Zr9Ta = 400 ~ 600ºC (1 h)1) Sm(Fe-Co)12-B• Highly oriented 1-12 phase was obtained below 500ºC, but it wasdecomposed above 600ºC.• High µ0Hc of 1.2 T was obtained in the deposited state but it decreasedwhen Ta was increased to 600ºC.2) Sm(Fe-Co)12-B / Zr• Decomposition of 1-12 phase was suppressed even at 600ºC.• High Ta resulted in the formation of ZrB2 and 1-5 phases.• µ0Hc of 0.47 T with perpendicular magnetic anisotropy was obtained at600ºC.3) Sm(Fe-Co)12-B / Nb• Decomposition of 1-12 phase was suppressed.• Peaks from NbB and 1-5 phase were observed at high Ta.• High µ0Hc of 0.96 T was obtained at 600 ºC.SummaryIn this study, in order to control the structure and improve the magneticproperties, stabilizing element such as Nb and Zr was selected as cappinglayer materials and post-annealed for Sm(Fe-Co)12-B thin film.Post annealed at Ta = 600 ºC10Detailed microstructural analysis by APT and HRTEM is currently being performed.