Highly tunable spin Hall magnetoresistance in room-temperature magnetoelectric multiferroic, Sr3Co2Fe24O41|Pt hybrids

Abstract

We present spin transport studies on a low-field, room-temperature magnetoelectric multiferroic polycrystalline Sr3Co2Fe24O41|Pt heterostructure wherein a highly tunable transverse conical magnetic phase is responsible for static and dynamic magnetoelectric coupling. We measured angular dependence of spin Hall magnetoresistance (SMR) at constant magnetic fields (H) in the range; 50–100 kOe. Application of field below the critical value (Hc1 ≈ 2.5 kOe), yielded negative SMR and the H-evolution of normalized SMR ((ΔR∕R0) × 100 %) exhibited a negative gradient. Further, an increase in H resulted in the positive slope of (ΔR∕R0) × 100 % Vs. H and later at higher H around 14 kOe, a crossover from negative to positive SMR was observed. We employed a simple model for estimating the equilibrium magnetic configuration and computed the SMR modulation at various values of H. We argue that the tilting of the cone is dominant and in turn responsible for the observed nature of SMR below 2.5 kOe while, the closing of the cone-angle is pronounced at higher fields causing a reversal in sign of the SMR from negative to positive. Importantly, SMR experiments revealed that a change in the helicity with a reversal of the magnetic field has no influence on the observed SMR. Longitudinal spin Seebeck effect (LSSE) signal was measured to be ≈ 500 nV at 280 K, under application of thermal gradient, ΔT = 23 K and field, 60 kOe. The observed LSSE signal, originating from pure magnon spin current, showed a similar H-dependent behavior as that of the magnetization of Sr3Co2Fe24O41. Our detailed spin transport studies on polycrystalline Sr3Co2Fe24O41|Pt heterostructure demonstrate high tunability of the amplitude and the sign of the SMR, highlighting its potential for novel spintronic devices such as SMR-based spin valves and voltage-controlled spin transport devices.