Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

Jai-Lin Tsai; Chun-Yu Sun; Jhih-Hong Lin; Yi-Yuan Huang; He-Ting Tsai

doi:10.3390/nano13030539

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

Nanomaterials (Basel). 2023 Jan 29;13(3):539. doi: 10.3390/nano13030539.

Authors

Jai-Lin Tsai¹, Chun-Yu Sun¹, Jhih-Hong Lin¹, Yi-Yuan Huang¹, He-Ting Tsai²

Affiliations

¹ Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan.
² Instrument Center, The Office of Research & Development, National Chung Hsing University, Taichung 402, Taiwan.

Abstract

A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (H_k) and perpendicular magnetocrystalline anisotropy (K_u),although the reference sample shows a higher value (H_k = 69.5 kOe, K_u = 1.74 × 10⁷ erg/cm³) than the FePt(BN, Re, C) film (H_k = 66.9 kOe, K_u = 1.46 × 10⁷ erg/cm³). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (H_c = 27 kOe), and both films present lower remanence (Mr_(parallel)/Mr_{(perpendicular)} = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin-orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (K_u). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively.

Keywords: columnar grains; granular structure; out-of-plane coercivity; perpendicular magnetocrystalline anisotropy; spin–orbital coupling.

Grants and funding

This research was funded by the Ministry of Science and Technology, Taiwan, grant number [MOST 111-2221-E-005-061]; Solar Applied Materials Technology Corp., Taiwan, grant number [110D610].