Perpendicularly magnetized τ-MnAl films have been epitaxied on GaAs (001) by molecular-beam epitaxy. Crystalline quality and magnetic properties of the samples were strongly dependent on growth temperature. The highest coercivity of 10.7 kOe, saturation magnetization of 361.4 emu/cm3, perpendicular magnetic anisotropy constant of 13.65 Merg/cm3, and magnetic energy product of 4.44 MGOe were achieved. These tunable magnetic properties make MnAl films valuable as excellent and cost-effective alternative for not only high density perpendicular magnetic recording storage and spintronics devices but also permanent magnets.

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Oxygen vacancy configurations and concentration are coupled with the magnetic, electronic, and transport properties of perovskite oxides, and manipulating the physical properties by tuning the vacancy structures of thin films is crucial for applications in many functional devices. In this study, we report a direct atomic resolution observation of the preferred orientation of vacancy ordering structure in the epitaxial LaCoO3–x (LCO) thin films under various strains from large compressive to large tensile strain utilizing scanning transmission electron microscopy (STEM). Under compressive strains, the oxygen vacancy ordering prefers to be along the planes parallel to the heterointerface. Changing the strains from compressive to tensile, the oxygen vacancy planes turn to be perpendicular to the heterointerface. Aberration-corrected STEM images, electron diffractions, and X-ray diffraction combined with X-ray photoelectron spectroscopy demonstrate that the vacancy concentration increases with increasing misfit strains and vacancy distribution is more ordered and homogeneous. The temperature-dependent magnetization curves show the Curie temperature increases, displaying a positive correlation with the misfit strains. With change in the strain from compressive to tensile, anisotropy fields vary and show large values under tensile strains. It is proposed that oxygen vacancy concentration and preferred ordering planes are responsible for the enhanced magnetic properties of LCO films. Our results have realized a controllable preparation of oxygen vacancy ordering structures via strains and thus provide an effective method to regulate and optimize the physical properties such as magnetic properties by strain engineering.

Abstract： The transport behaviors of weak localization and anomalous Hall effect (AHE) in perpendicularly magnetized L1 0 -Mn 1.5 Ga single-crystalline films are investigated as a function of degree of long-range chemical ordering and temperature. We observed significant weak localization and metal-insulator transition in highly disordered films. Our results provide new evidence that weak localization, phonons and magnons have negligibly smaller effect on extrinsic AHE resistivity than static defects for all the chemical disordered films, the overlook of which in conventional scaling laws may result in significant discrepancies and exponent n beyond 2 when fitting the data. Chemical disorder is found to exhibit strong tailoring effect on both intrinsic and extrinsic σ AH . Our results clarify the role of weak localization, phonons and magnons in AHE and offer a technological engineering approach of the AHE by altering long-range chemical ordering parameter of magnetic materials. Key words：Weak localization, Anomalous Hall effect, Chemical disorder, Perpendicular magnetic anisotropy, PACS: 72.15. Rn, 81.30.Hd, 75.30.Gw a) Author to whom correspondence should be addressed; Electronic mail: jhzhao@red.semi.ac.cnThe anomalous Hall effect (AHE) has attracted much attention due to both the fascinating underlying physics and the great application potential in sensors, memories and logics. [1][2][3][4][5][6][7][8] It is widely accepted that there are three mechanisms responsible for the AHE. The intrinsic AHE arises from the transverse velocity of the Bloch electrons induced by SOI and interband mixing, 9 as experimentally evidenced by quantum anomalous Hall effect. 10 The extrinsic mechanisms of skew scattering and side jump result from the impurity scattering of conduction electrons due to SOI. 11,12 Skew scattering yields a scaling relation between longitudinal resistivity ρ xx (conductivity σ xx =1/ρ xx ) and anomalous Hall resistivity ρ AH (conductivity σ AH ≈ρ AH /ρ xx 2 ) as ρ AH~ρxx , while other two mechanisms give ρ AH~ρxx 2 . Accordingly, scaling laws ρ AH~ρxx n and ρ AH =aρ xx +bρ xx 2 are conventionally used to describe the experimental data.In spite of the extensive studies, a unified scaling of AHE has remained a shortage. In stark contrast to present AHE theories, the exponent n was experimentally observed to be below 1 or beyond 2 in a variety of ferromagnets, e.g. 0.4 in hopping transport-accompanied Fe 3 O 4 films, 13 2.7 (2.85) in (111)-orientated Mn 2.03 Ga (Mn 1.38 Ga) films, 14 2.6 in Fe/Cr multilayers 15 and 3.7 in Co-Ag granular films. 16 Electron localization was recently found to yield a scaling with n=0 in chemically disordered FePt ultrathin films. 17 Noticeably, recent studies in Fe films revealed a negligible contribution of phonon skew scattering and a scaling ρ AH =a 0 ρ xx0 +bρ xx 2 , where a 0 ρ xx0 = α 0 ρ xx0 +βρ xx0 2 is the extrinsic contributions of skew scattering and side jump from static defects. 3 These intriguing observations make the scaling of AHE open questions. On the o...

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