Exploring Doping Effects on Magnetocaloric, Magnetoelastic, and Magnetostriction Properties of Fe2AlB2: A First-Principles Study

Fe2AlB2 boasts promising magnetocaloric properties and anisotropic magnetic behavior. This study explores the impact of elemental substitutions on its magnetic and magnetocaloric properties using density functional theory, the cluster expansion method, and Monte Carlo simulations. Results show that doping at Fe or B sites induces a rotation of the easy axis of magnetization and noticeably changes the magnitude of magnetic anisotropy energy. Predicted Curie temperatures are 308, 210, and 359 K for Fe2AlB2, Fe2GaB2, and Fe2SiB2, respectively. The magnetic entropy change exhibits anisotropic behavior, especially near the transition temperature. Interestingly, full substitution of Al with Ga or Si does not significantly enhance the magnetic entropy change, suggesting other factors play a dominant role in enhancing magnetocaloric properties of these materials. Therefore, our study delves into magnetostructural coupling and defect formation due to partial chemical substitutions. The C doping induces substantial lattice parameter changes, Si, Ga, and Ge doping improves magnetocaloric properties, while Cr and V doping reduces magnetostructural coupling. Antisite defect formation at the Al site are induced by Fe near Ga, Ge, and Si atoms, indicating enhanced defect formation and increased saturation magnetization. Fe2AlB2 exhibits anisotropic features in its magnetoelastic constants and magnetostrictive coefficients. This implies that the material's response to changes in magnetic fields is contingent on the orientation of its crystal lattice, and, additionally, Fe2AlB2 can experience expansion or contraction along distinct crystallographic directions in response to alterations in the magnetization direction.