Role of spin-orbit coupling in spin-to-lattice energy conversion in ferrite nanoparticles.

We report on the influence of spin-orbit coupling (SOC) in governing spin-to-lattice energy conversion in ferrite nanoparticles (MnFe2O4, Fe3O4, and NiFe2O4). Using infrared thermography, ferromagnetic resonance measurements, and numerical temperature-profile fitting based on an analytical thermal model, we successfully identify and clarify distinct energy conversion pathways. Specifically, we decompose the process into three sequential steps: field-to-spin energy transfer, spin precession and relaxation, and spin-to-lattice heat conversion. Our quantitative analysis reveals that spin-to-lattice conversion efficiencies are found to be approximately 21%, 18%, and 16% for the Fe, Ni, and Mn ferrites, respectively. These values closely follow the trends in the estimated Landé g-factors and SOC strengths. While SOC plays a dominant role in determining spin-to-lattice conversion efficiency, we emphasize that the total heat output also depends on intrinsic spin relaxation power, as evidenced from the high thermal response of MnFe2O4 despite its relatively weaker SOC. Our findings provide a quantitative framework for understanding SOC-mediated spin-to-lattice thermal conversion and offer material design guidelines for spin-caloritronics, nanoscale thermal management, and energy dissipation applications.