Abstract: Magnetic refrigeration based on the magnetocaloric effect (MCE) is a novel refrigeration technology that will replace traditional vapor-compression refrigeration in the future. Improvement in the performance of MCE materials is crucial for the development of magnetic refrigeration technology. This study presents a new method that enhances the MCE performance of (Sc,Ti)Fe₂ via magnetic phase separation. The maximum magnetic entropy change induced by the coexistence of an in-plane ferromagnetic phase (FM^ab) and a canting antiferromagnetic phase (CAFM) in Sc_0.3Ti_0.7Fe₂ is twice that found in other (Sc,Ti)Fe₂ compounds. Variable-temperature neutron diffraction experiments directly reveal that the large magnetic entropy change in Sc_0.3Ti_0.7Fe₂ is dominated by the transformation from a highly ordered FM^ab state to a CAFM state with a lower magnetic order. The magnetic phase separation is a direct transition from a higher-ordered state with a larger lattice to a lower-ordered state with a smaller lattice that induces a large magnetic order change and lattice contraction. The combination of the metamagnetic transition and negative thermal expansion leads to enhanced MCE. This study suggests the possibility that magnetic phase separation can be an effective approach to achieving and controlling a large MCE in magnetic materials.

Key words: Magnetocaloric effect, Neutron diffraction, Magnetic structure