Effects of interstitial C atoms on magnetostructural transformation and magnetocaloric effect in MnNi0.77Fe0.23GeCx compounds

Abstract

In this study, the influence of interstitial C atoms on the magnetostructural transformation and magnetocaloric effect in MnNi0.77Fe0.23GeCx (x = 0, 0.02, and 0.03) compounds has been investigated. The introduction of C atoms into the interstitial sites of the MnNi0.77Fe0.23Ge compounds leads to the enhanced stability of the orthorhombic phase, thus enhancing the structural transition temperature. Moreover, the critical field of antiferromagnetic (AFM)–ferromagnetic (FM) conversion significantly decreases following C atom incorporation. Therefore, it can be inferred that C atoms can promote the AFM–FM conversion in the TiNiSi-type orthorhombic phase. The MnNi0.77Fe0.23GeCx compound with x = 0.02 exhibits a large magnetocaloric effect due to the ferromagnetic magnetostructural transition. Furthermore, for the compound with x = 0.03, a table-like magnetocaloric effect is observed around room temperature owing to the coupling of the martensitic and metamagnetic transitions, which confirms the wide working temperature range and a large refrigerant capacity.