Giant perpendicular exchange bias with antiferromagnetic MnN

Zilske P, Graulich D, Dunz M, Meinert M. Giant perpendicular exchange bias with antiferromagnetic MnN. Applied Physics Letters. 2017;110(19): 192402.We investigated an out-of-plane exchange bias system that is based on the antiferromagnet MnN. Polycrystalline, highly textured film stacks of Ta/MnN/CoFeB/MgO/Ta were grown on SiOx by (reactive) magnetron sputtering and studied by x-ray diffraction and Kerr magnetometry. Nontrivial modifications of the exchange bias and the perpendicular magnetic anisotropy were observed as functions of both film thicknesses and field cooling temperatures. In optimized film stacks, a giant perpendicular exchange bias of 3600Oe and a coercive field of 350 Oe were observed at room temperature. The effective interfacial exchange energy is estimated to be J(eff) = 0.24 mJ/m(2) and the effective uniaxial anisotropy constant of the antiferromagnet is K-eff = 24 kJ/m(3). The maximum effective perpendicular anisotropy field of the CoFeB layer is H-ani = 3400 Oe. These values are larger than any previously reported values. These results possibly open a route to magnetically stable, exchange biased perpendicularly magnetized spin valves. Published by AIP Publishing

Optimization of ruthenium as a buffer layer for non-collinear antiferromagnetic Mn3X films

Kurdi S, Zilske P, Xu XD, et al. Optimization of ruthenium as a buffer layer for non-collinear antiferromagnetic Mn3X films. JOURNAL OF APPLIED PHYSICS. 2020;127(16): 165302.Two thin film deposition routes were studied for the growth of high quality single crystalline Ru (0001) epitaxial films on c-Al2O3 substrates using radio frequency-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 degrees C, leading to a smooth 30nm thick film. Although, high resolution x-ray diffraction revealed twinned Ru film orientations, 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 the deposition of Ru at room temperature followed by in situ post-annealing at 700 degrees C. Transmission electron microscopy confirmed a very high quality of these films, free of crystal twinning, and a 30 degrees 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 7nm thickness. 30nm 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. Published under license by AIP Publishing