Emergent Antisymmetric\nMagnetoresistance in Ferromagnetic\nNi/Pt Bilayers with Enhanced Spin–Orbit Torque Efficiency:\nImplications for Low-Temperature Nano-oscillators

We\nreport an unconventional out-of-plane magnetoresistance with\nan antisymmetric component in Ni/Pt bilayers with in-plane magnetization\nanisotropy emerging at low temperatures below 100 K, dramatically\ndistinct from the observed conventional symmetric magnetoresistance\nat elevated temperatures or when the field is rotated to in-plane.\nThe observed magnetoresistance is antisymmetric to the magnetic field\nand changes sign with opposite applied current but symmetric when\nthe magnetic field and current both have a reverse sign. Ferromagnetic\nresonance (FMR) signals show an enhanced spin–orbit torque\nefficiency when the temperature is reduced from 300 to 100 K, and\nan extra resonance peak appears under an out-of-plane magnetic field\nat around 50 mT, under similar conditions as the emergent antisymmetric\nmagnetoresistance peak. We attribute the observed antisymmetric magnetoresistance\nto the enhanced spin–orbit-torque efficiency in Ni/Pt bilayers\nwith thicknesses of tens of nanometers at low temperatures.