Highly tunable spin Hall magnetoresistance in magnetoelectric multiferroic Z-type hexaferrite, Sr₃Co₂Fe₂₄O₄₁|Pt hybrids

We present spin transport studies on a low-field, room-temperature magnetoelectric multiferroic polycrystalline Sr₃Co₂Fe₂₄O₄₁|Pt heterostructure wherein, a transverse conical magnetic phase is responsible for static and dynamic magnetoelectric coupling. We measured angular dependence of spin Hall magnetoresistance (SMR) at various constant magnetic fields (H) in the range, 50 Oe to 100 kOe. Fields below a critical value of 2 kOe, yielded a negative SMR and SMR amplitude vs. H exhibited a negative gradient. Further, increase in the H resulted in the positive slope of SMR amplitude vs. H and near H ≈ 14 kOe, a crossover observed from negative to positive SMR. We employed a simple model to compute and understand SMR in Sr₃Co₂Fe₂₄O₄₁. We argue that the cone-tilting is dominant and in turn responsible for the observed nature of SMR below 2 kOe while, closing of the cone-angle is pronounced at higher H causing a reversal in sign of the SMR from negative to positive. Notably, SMR studies revealed that a change in the helicity with a reversal of H has no influence on the observed SMR. Our detailed spin transport studies on Sr₃Co₂Fe₂₄O₄₁ demonstrate high tunability of the amplitude and the sign of the SMR highlighting its potential for magnetoresistance-based spintronic devices.