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.