Competing local and nonlocal spin Hall magnetoresistance signals in MgO|Ni_0.8Zn_0.2F₂O₄|NiO|Pt heterostructure

Recently, the insertion of passive antiferromagnetic (AFM) layers was found to play a crucial role in magnon spin valves [1]. Electrically and/or thermally injected magnon spin currents and their transport across insulating AFM and ferrimagnetic (FM) layers have been under scrutiny in the past few years. Interestingly, in heterostructure devices consisting of FM|AFM|heavy metal (HM) stack, local spin Hall magnetoresistance (SMR) and non-local magnon-mediated SMR signals compete [2].

In this work, MgO(001)|Ni_0.8Zn_0.2F₂O₄(NZFO)|NiO|Pt stack was prepared by the pulsed LASER deposition method. To examine local and nonlocal SMR contributions in 1w and 2w SMR measurements, MgO|NZFO|NiO|Pt stack was prepared with different thicknesses (t = 0 to 4 nm) of the NiO layer. Contrasting (opposite sign of SMR) and distinct (active vs. passive with respect to thermal magnon generation) behaviors of FM and AFM layers determine the overall SMR signal. Our spin transport measurements over a wide temperature-magnetic field parameter space helped us probe the role of magnetic anisotropies associated with FM and AFM layers and interfacial exchange coupling on the spin accumulation in the Pt-layer and in turn, the net SMR signal.

[1] Guo et al. PRB 98, 134426 (2018)

[2] Guo et al. Nat Electron 3, 304–308 (2020)