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High-entropy alloys (HEAs) exhibit various physical properties, such as high microhardness for structured materials and high efficiency for catalysis. These features are recognized as a cocktail effect of five or more elements that stabilize a single-phase solid solution due to a high configurational entropy. HEAs may also exhibit short-range orders and microdistortions, which cause the local symmetry breaking of systems. Systems with local symmetry breaking are of interest for spin-dependent transport, such as for spin Hall effects. In this study, sputtered-film samples of an HEA, Mn-Nb-Mo-Ta-W, and related alloys, were fabricated; these films were layered with ferromagnetic CoFeB. All samples exhibited x-ray diffraction peaks originating only from a body-centered-cubic (bcc) phase, and transmission electron microscopy images indicated the absence of secondary phases and uniform elemental distributions. The spin Hall magnetoresistance (SMR) was investigated, and clear resistance changes were observed in all the samples. Quantitative analysis of SMR revealed that the spin Hall angle (ₒ₇) was 0. 120. 002 and 0. 140. 037 for the HEA and Nb-Mo-Ta-W alloy medium-entropy alloy (MEA), respectively. The ₒ₇'s of the HEA and MEA were comparable to that of Pt which is a typical heavy element with relatively large ₒ₇. The recently developed HEA and MEA films are attractive spin Hall materials with the bcc phase and are suitable for spintronic applications using magnetic tunnel junctions with CoFeB and an MgO barrier.
Kubota et al. (Wed,) studied this question.