A large perpendicular magnetic anisotropy (PMA) of 1.4 MJ/m3 was observed from ultrathin Fe/MgO(001) bilayers grown on Cr-buffered MgO(001). The PMA strongly depends on the surface state of Fe prior to the MgO deposition. A large PMA energy density of 1.4 MJ/m3 was achieved for a 0.7 nm thick Fe layer having adsorbate-induced surface reconstruction, which is likely to originate from oxygen atoms floating up from the Cr buffer layer. This large magnitude of PMA satisfies the criterion that is required for thermal stability of magnetization in a few tens nanometer-sized magnetic memory elements.

A 4-fold-symmetry hexagonal Ru emerging in epitaxial MgO/Ru/Co2 FeAl/MgO heterostructures is reported, in which an approximately Ru(022¯3) growth attributes to the lattice matching between MgO, Ru, and Co2 FeAl. Perpendicular magnetic anisotropy of the Co2 FeAl/MgO interface is substantially enhanced. The magnetic tunnel junctions (MTJs) incorporating this structure give rise to the largest tunnel magnetoresistance for perpendicular MTJs using low damping Heusler alloys.

Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent x-ray magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3dz2 and O 2pz states.

The recently reported MgAl2O4 tunnel barrier for the magnetic tunnel junctions (MTJs) is considered to be an alternative to the conventional MgO barrier, since a large tunnel magnetoresistance (TMR) ratio was obtained for the MgAl2O4‐based MTJs. In this study, we demonstrated large perpendicular magnetic anisotropy (PMA) arising from the interfaces of Fe(001)/MgAl2O4 layered structures, which can be useful for developing perpendicularly magnetized MgAl2O4‐based MTJs. A PMA energy density of 0.4 MJ/m3 was achieved for an epitaxially grown 0.7 nm thick Fe/MgAl2O4(001). Interestingly, the interface PMA was also obtained for the Fe/non‐epitaxially grown MgAl2O4 structures, which indicates that the crystallographic structure of MgAl2O4 layer has no critical influence on the obtained PMA. Large interface perpendicular magnetic anisotropy in the epitaxially grown Fe (0.7 nm)/MgAl2O4 layered structure (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The agglomeration phenomena of a few nanometer thick Au/Fe bilayers, grown on an MgO(100) substrate, were studied by using atomic force microscopy and x ray diffraction (XRD). The authors found that the insertion of an Fe ultrathin layer between an MgO(100) substrate and a 4 nm thick Au layer promotes the agglomeration process of the Au layer, in which the bilayer structure changes into large Fe/Au islands of ∼200 nm in diameter. In addition, XRD results revealed that the Au in the agglomerated islands has only a (111)-crystallographic orientation, presumably caused by reducing the large surface energy of Au on the MgO(001) substrate. These findings are quite different from cases in which structural stabilization is achieved by inserting an Fe seeding layer of a few nanometers on an MgO(001) substrate.

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We fabricated self-organized FePd multilayer films with specific nanostructures by using Au/Fe bilayer films as a template. Au/Fe bilayer films were prepared as a template layer by forming a self-organized nanostructure through the agglomeration phenomenon. Using this Au/Fe bilayer as a template, FePd multilayers were deposited. The surface morphologies of FePd multilayer closely resembled the self-organized Au/Fe bilayer. As a result, we successfully manufactured self-organized FePd nanodots, with a shape closely resembling that of the agglomerated Au/Fe bilayer. In addition, it is confirmed that the agglomerated FePd nanodots were formed in the L10 phase by annealing at 350 °C.

Two thin film deposition routes were studied for the growth of high quality single crystalline Ru (0001) epitaxial films on c-Al2O3 substrates using RF-magnetron sputtering. Such films are very important as buffer layers for the deposition of epitaxial non-collinear antiferromagnetic Mn3X films. The first route involved depositing Ru at 700 °C, leading to a smooth 30 nm thick film. Although, high resolution X-ray diffraction (HRXRD) revealed twinned Ru film orientations, the in-situ post-annealing eliminated one orientation, leaving the film orientation aligned with the substrate, with no in-plane lattice rotation and a large lattice mismatch (13.6%). The second route involved deposition of Ru at room temperature followed by in-situ post-annealing at 700 °C. Transmission electron microscopy confirmed a very high quality of these films, free of crystal twinning, and a 30° in-plane lattice rotation relative to the substrate, resulting in a small in-plane lattice mismatch of -1.6%. X-ray reflectivity demonstrated smooth surfaces for films down to 7 nm thickness. 30 nm thick high quality single-crystalline Mn3Ga and Mn3Sn films were grown on top of the Ru buffer deposited using the second route as a first step to realize Mn3X films for antiferromagnetic spintronics applications.