The recent discovery of perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO interface has accelerated the development of next generation high-density non-volatile memories by utilizing perpendicular magnetic tunnel junctions (p-MTJs). However, the insufficient interfacial PMA in the typical Ta/CoFeB/MgO system will not only complicate the p-MTJ optimization, but also limit the device density scalability. Moreover, the rapid decreases of PMA in Ta/CoFeB/MgO films with annealing temperature higher than 300°C will make the compatibility with CMOS integrated circuits a big problem. By replacing the Ta buffer layer with a thin Mo film, we have increased the PMA in the Ta/CoFeB/MgO structure by 20%. More importantly, the thermal stability of the perpendicularly magnetized (001)CoFeB/MgO films is greatly increased from 300°C to 425°C, making the Mo/CoFeB/MgO films attractive for a practical p-MTJ application.
Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (Ms) and the coercive field (Hc) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (jc) of 2.5 × 106 A/cm2, an order of magnitude smaller than the previously reported value. We were able to tune Ms, Hc and H⊥ to obtain an ultra-low jc of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.
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