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We report on a spin-orbit torque study of the spin current generation in Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer, with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find that the spin current generation in the Cr1-xPtx alloy can be fully understood by the characteristic trade-off between the intrinsic spin Hall conductivity of Pt and the carrier lifetime in the dirty limit. We find no evidence for the spin current generation by other mechanisms in this material, revealing that the role of Cr is found to be simply the same as other metals and oxides in previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as an energy-efficient spin-orbit torque provider for magnetic memory and computing technologies.

Efficient manipulation of antiferromagnetically coupled materials that are integration-friendly and have strong perpendicular magnetic anisotropy (PMA) is of great interest for low-power, fast, dense magnetic storage and computing. Here, we report a distinct, giant bulk damping-like spin-orbit torque in strong-PMA ferrimagnetic Fe100-xTbx single layers that are integration-friendly (composition-uniform, amorphous, sputter-deposited). For sufficiently-thick layers, this bulk torque is constant in the efficiency per unit layer thickness, {\xi}_DL^j/t, with a record-high value of 0.036nm-1, and the dampinglike torque efficiency {\xi}_DL^j achieves very large values for thick layers, up to 300% for 90 nm layers. This giant bulk torque by itself switches tens of nm thick Fe100-xTbx layers that have very strong PMA and high coercivity at current densities as low as a few MA/cm2. Surprisingly, for a given layer thickness, {\xi}_DL^j shows strong composition dependence and becomes negative for composition where the total angular momentum is oriented parallel to the magnetization rather than antiparallel. Our findings of giant bulk spin torque efficiency and intriguing torque-compensation correlation will stimulate study of such unique spin-orbit phenomena in a variety of ferrimagnetic hosts. This work paves a promising avenue for developing ultralow-power, fast, dense ferrimagnetic storage and computing devices., Comment: To appear in Applied Physics Reviews

The generation of perpendicular effective magnetic field or perpendicular spins ( σz) is central for the development of energy-efficient, scalable, and external-magnetic-field-free spintronic memory and computing technologies. Here, we report the first identification and the profound impacts of a significant effective perpendicular magnetic field that can arise from asymmetric current spreading within magnetic microstrips and Hall bars. This effective perpendicular magnetic field can exhibit all the three characteristics that have been widely assumed in the literature to “signify” the presence of a flow of σz, i.e., external-magnetic-field-free current switching of uniform perpendicular magnetization, a sin 2 φ-dependent contribution in spin-torque ferromagnetic resonance signal of in-plane magnetization ( φ is the angle of the external magnetic field with respect to the current), and a φ-independent but field-dependent contribution in the second harmonic Hall voltage of in-plane magnetization. This finding suggests that it is critical to include current spreading effects in the analyses of various spin polarizations and spin–orbit torques in the magnetic heterostructure. Technologically, our results provide a perpendicular effective magnetic field induced by asymmetric current spreading as a novel, universally accessible mechanism for efficient, scalable, and external-magnetic-field-free magnetization switching in memory and computing technologies.