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MMM 2022

November 07, 2022

Minneapolis, United States

Suppression of the formation of soft magnetic phase for Sm(Fe Co) thin films by introducing Sm seed layer

Sm(Fe0.8Co0.2)12 thin films with the ThMn12 type crystal structure are expected as a new high-performance permanent magnet material because they possess excellent magnetic properties such as high saturation magnetization µ0Ms of 1.78 T, anisotropy field µ0HA of 12 T and Curie temperature TC of 879 K 1. Recently, it has been clarified that a coercive force µ0Hc as high as 1.2 T can be successfully obtained in the Sm(Fe-Co) thin films with B addition. It is considered that this is mainly due to the formation of RFe12 grains with columnar structure separated by the B-rich amorphous grain boundary phase 2. In addition, µ0Hc was further increased by the diffusion of Si into the grain boundary phase in the Sm(Fe-Co)-B thin films. Then, it is predicted that µ0Hc will be further increased by reducing the soft magnetic phase existing at the vicinity of the initial interface between V under layer and Sm(Fe-Co)-B main layer 3. In this study, a Sm seed layer was inserted between the V under layer and the Sm(Fe-Co) layer to suppress the initial growth of soft magnetic phase such as α-Fe and α-(Fe-Co), and the crystal structure and magnetic properties were investigated in detail. The samples were prepared by using the ultra-high vacuum magnetron sputtering system. First of all, a V buffer layer of 20 nm was deposited onto the MgO (100) single crystal substrate at substrate temperature Ts of 673 K. Then, the thickness tSm of the Sm seed layer was changed from 0 to 5 nm and while that of Sm(Fe-Co)-B layer was fixed at 100 nm. Finally, a V cover layer of 10 nm was deposited. The B composition was changed up to 5 at.%. It was confirmed that the introduction of the Sm seed layer into Sm(Fe-Co) layer clearly decreases the intensity of the peaks obtained from α-(Fe-Co) and increases the intensity of the (002) and (004) peaks in the RFe12 phase. In addition, improvement of remanent magnetization ratio while maintaining µ0Hc above 1.0 T was confirmed. It was thought that the Sm seed layer plays an important role to suppress the formation of α-(Fe-Co) phase and to improve the orientation of the 1:12 phase. The detailed results will be discussed at the conference.
1 Y. Hirayama, Y. K. Takahashi, S. Hirosawa and K. Hono, Scr. Mater., 138 (2017) 62-65.
2 Sepehri-Amin, Y. Tamazawa, M. Kambayashi, G. Saito, Y. K. Takahashi, D. Ogawa, T. Ohkubo, S. Hirosawa, M. Doi, T. Shima, K. Hono, Scr. Mater., 194 (2020) 337-342.
3 A. Boyachkin, H. Sepehri-Amin, M. Kambayashi, Y. Mori, T. Ohkubo, Y. K. Takahashi, T. Shima, K. Hono, Acta. Mater., 227 (2022) 117716.

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Jianjun Yang and 6 other authors

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