Spin current generation in spinel-ferrite/Cu/Pt heterostructures

Understanding spin-pumping at the interface between low-damping magnetic oxides and normal metals with large spin-orbit coupling (e.g. Pt) is crucial to the development of "pure" spin current spintronic devices. We demonstrate that the spinel-ferrite (Ni,Zn)(Al,Fe)₂O₄ is a low loss spin current source on par with Y₃Fe₅O₁₂ (YIG). Broadband ferromagnetic resonance (FMR) spectroscopy shows a low Gilbert damping parameter of α ≈ 0.003 for 15-nm thick single-layer NZAFO. In NZAFO/Pt bilayers the damping parameter increases to α ≈ 0.009 accompanied by a voltage peak coinciding with FMR, suggesting significant spin pumping from NZAFO to Pt with a spin-mixing conductance of ~2×10¹⁴ Ω^-1m^-1. To investigate the possible contribution of proximity induced magnetism (PIM) in the Pt layer, we insert Cu spacer layers at the NZAFO/Pt interface. Similar damping enhancement and FMR-driven voltage are detected in NZAFO/Cu/Pt, and angular dependent magnetoresistance measurements show an order of magnitude larger spin-Hall magnetoresistance compared to PIM-induced anisotropic magnetoresistance. Our results demonstrate that the observed FMR-driven voltage is dominated by spin pumping from the ferrite layer through the copper into the platinum layer, with a minimal contribution from PIM in the Pt layer.