Lattice Contribution to the Magnetocaloric Entropy Change: A Spin-Lattice Dynamics Study

We present an efficient computational approach for understanding the lattice contribution to the magnetocaloric effect in bcc iron (Fe) and hcp gadolinium (Gd) using spin-lattice dynamics, with exchange coupling parameters determined from ab initio calculations. The simulated magnetic transition temperature using the current approach gives better agreement with the experimental measurements. We find that the presence of long-range indirect (RKKY type) exchange in hcp Gd strongly influences the low-frequency long-wavelength phonons at higher applied external magnetic fields. This results in a higher lattice contribution towards the total magnetocaloric entropy change as compared to bcc Fe with short-range direct exchange couplings. The current developed approach provides a viable framework for understanding the magnetocaloric effect in complicated magnetic materials with strong spin-lattice coupling. Our finding suggests that long-range indirect exchange leads to a larger lattice contribution to the magnetocaloric entropy change and is thus beneficial for magnetocaloric materials.