Investigation of Amorphous SmFe2 Thin Films With Giant Negative Magnetostriction and Perpendicular Magnetic Anisotropy

In this paper, we systematically investigated magnetic anisotropy and magnetostriction of sputtered SmFe₂ thin films, and found that amorphous SmFe₂ films showed PMA and large, negative λ. All the films were prepared with a facing targets sputtering system. The stack structure was quartz-substrate/W (20nm)/Sm-Fe (100nm)/W (10nm). The substrate temperature T_s during sputtering varied from RT to 400°C. The post annealing temperature T_A also varied from 300°C to 600°C. The chemical composition of deposited Sm-Fe film was determined to be 1.05:2 by inductively coupled plasma-optical emission spectrometer (ICPOES). X-ray diffraction (XRD) analysis showed that all of the fabricated SmFe₂ thin films had amorphous structure. we found that Sm_1.05Fe₂ thin films formed at low T_s and annealed at high T_A showed PMA. One of the possible origins of th is PMA is the anisotropic, short range order of Sm and Fe atoms. The Sm_1.05Fe₂ film with T_s = 200°C and T_A = 500°C exhibiting PMA also showed large, negative magnetostriction λ = -920 ppm. This result indicates that Sm_1.05Fe₂ thin fi lms are promising as the free layer of IMS-MTJ for ultra -low energy STT-MRAMs.