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We have developed a new non-destructive sub-surface interfacial imaging technique. By controlling the penetration depth of the incident electrons, through control of the electron beam acceleration voltage in a scanning electron microscope, we can observe sub-surface interfaces. The voltages for imaging are selected based on Monte Carlo electron flight simulations, where the two voltages have  >5% difference between the number of backscattered electrons generated in the layers above and below the buried interface under investigation. Due to the non-destructive nature, this imaging method can be used alongside an applied electrical current and voltage, allowing concurrent observations of the interfacial structures and transport properties, e.g. effective and active junction area, to occur. Magnetic tunnel junctions used in magnetic random access memory have been imaged and the data has been fed back to improve their fabrication processes. Our imaging method is therefore highly useful as both a quality assurance and development tool for magnetic memory and nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Magnetic materials with low Gilbert damping and low magnetization are necessary for the realization of faster or more energy-efficient spintronic devices based on spin-transfer-torque. Here, we report Gilbert damping in epitaxially grown equiatomic quaternary CoFeMnSi Heusler alloy films. The 10 nm-thick films show a saturation magnetization of MS  =  630 emu cm−3 and a Gilbert damping constant of , which are relatively small values among transition metal ferromagnets, in addition to its soft magnetic properties. The physical origin of the relatively low damping and the possibility of a further reduction of α to the ultra-low damping regime  ∼10−4 are discussed in terms of the spin-gapless-like electronic structure and the effect of the chemical order computed from first principles. [ABSTRACT FROM AUTHOR]

L10 MnGa is one of the interesting magnetic alloys for spin-transfer-torque based applications because such alloys have high perpendicular magnetic anisotropy, small magnetization, and low Gilbert damping. Magnetic tunnel junctions (MTJs) with ultrathin MnGa electrodes have recently been demonstrated using the room temperature growth technique of MnGa on paramagnetic B2-ordered CoGa templates, which exhibited a small TMR ratio of  ∼3%. To obtain a higher TMR ratio, we systematically investigated the annealing dependence of the TMR ratio with MTJs with 1–5 nm thick MnGa electrodes in this study. The TMR ratios were 2%–3% without annealing, which were the same as those reported previously, and the TMR ratios reached their maximum values of 6%–8% at an annealing temperature of approximately 250 °C for the MTJs with 2–5 nm MnGa electrodes. The TMR ratio increased to approximately 25% at 10 K for those MTJs. These TMR ratios were slightly higher than those reported in MTJs with 30 nm-thick MnGa electrodes. The annealing temperature at which TMR showed the maximum value tended to decrease with decreasing MnGa thickness, and this low annealing endurance may be attributed to the atomic mixing between MnGa and barrier/buffer layers. The TMR ratio was discussed in terms of both coherent tunneling based on first principles calculations with different element terminations at the interface and incoherent tunneling. [ABSTRACT FROM AUTHOR]

We investigated the structure and magnetic properties of epitaxial films of D022-Mn3Ge tetragonal Heusler like compounds in detail. Epitaxial films with a stoichiometric composition were grown on Cr-buffered single crystalline (0 0 1) MgO substrates using ultra-high vacuum sputtering at different growth temperatures. X-ray diffraction showed that D022-ordered films were formed at growth temperatures of ⩾200 °C. Epitaxial growth was indicated by cross-sectional high-resolution transmission electron microscopy. Nanobeam diffraction patterns from the D022-Mn3Ge film grown at 400 °C suggests the absence of planar defects such as stacking faults and twins in the film. Out-of-plane magnetic hysteresis curves with perfect squareness were observed for the films grown at ⩾300 °C. These films also showed abrupt magnetization reversal at a coercivity of about 1 T, which is higher than that of other thin film materials with perpendicular magnetic anisotropy such as CoPt and FePt. A huge domain diameter in the D022-Mn3Ge films was indicated by the initial magnetization curves that were measured by the polar magneto-optical Kerr effect. [ABSTRACT FROM AUTHOR]