Spin-Current Generation in Low-Damping N0.65Zn0.35Al0.8Fe12O4 Spinel Ferrite

Low-damping spin sources are critical to efficient spin-current generation, but low-damping magnetic insulators have not been systematically explored so that the controlling parameters for efficient spin-current generation are not well understood. The choice of magnetic insulators with sufficiently low damping has been largely limited to Y3Fe5O12 (YIG), whose compatibility with existing microelectronics is problematic at best. Therefore, an alternative material or family of magnetic insulators with low damping would provide not only fundamental insight into the underlying mechanisms for low-damping magnetic insulators but also the foundation for a spin-current-based electronics future. The family of spinel ferrites includes a wide variety of magnetic insulators, but high damping in conventional spinel ferrites has made them poor spin-current sources. In this study, we demonstrate that microwave excitation of low-damping (Ni, Zn, Al) ferrite (NZAFO) efficiently generates spin current. Spin pumping from the ferrite to an adjacent metal layer is manifest in both an increase in Gilbert damping and the emergence of a voltage peak that occurs at ferromagnetic resonance (FMR). Magnetotransport measurements suggest negligible contributions from a proximity-induced magnetic layer in the metal. From FMR and magnetotransport measurements, we estimate the spin-mixing conductance at the NZAFO/Pt interface to be approximately 10(14) Omega(-1) m(-2), on the same order of magnitude as the often-studied YIG/Pt interface. These results indicate that doped spinel ferrites can be efficient spin-pumping sources with a potential for highly tunable magnetic properties and coherent integration with a diverse range of complex oxides for all-oxide spintronics.