Phase separation and combination of negative and positive magnetocaloric effects in Mn3Ga1−xAxC (A = Sn, Ge, Y)

Abstract

Mn3GaC exhibits both negative and positive magnetocaloric effects (NMCE and PMCE). Herein, to fabricate high-performance magnetic refrigerants, enhancement of the magnetocaloric effect (MCE) by combining NMCE and PMCE is studied. Compared with composite magnetic refrigerants, an NMCE-PMCE combination in a single magnetic refrigerant considerably enhances the operating temperature range without any loss of magnetic entropy change or relative cooling power (RCP). To realize an NMCE-PMCE combination, the NMCE and PMCE must be clearly identified. The intermediate canted ferromagnetic phase (CFM) between the antiferromagnetic and ferromagnetic phases of Mn3GaC plays a key role in establishing the borderline between the NMCE and PMCE. The effects of substituting Sn, Ge, and Y for Ga on the magnetic phase separation, NMCE, and PMCE of Mn3Ga1−xAxC (A = Sn, Ge, Y) are investigated. Y doping considerably enhances the CFM state, which establishes a buffer region between the NMCE and PMCE in Mn3Ga0.97Y0.03C. Because of this buffer region, the NMCE and PMCE can be controlled in different temperature ranges for practical applications. We achieve an NMCE-PMCE combination and obtain a super-wide working temperature range in Mn3Ga0.97Y0.03C. This work will be helpful in developing a practical magnetocaloric material with a large MCE and a working temperature range.