Magnetic phase transition and magneto-caloric effect (MCE) in (Mn_0.5Ni_0.5)_60+xGa_40-x (x = 3.3, 5.0, and 6.6) alloys

A systematic investigation of rare earth free magnets (Mn_0.5Ni_0.5)_60+xGa_40-x (x = 3.3, 5.0, and 6.6) which are typical skyrmion hosting alloys are presented with respected to the crystal structure, magnetic phase transition and magneto-caloric effect (MCE). All the (Mn_0.5Ni_0.5)_60+xGa_40-x alloys exhibit a hexagonal Ni₂In-type structure with the P63/mmc space group confirmed by X-ray diffraction. The Mn and Ga/Ni atomic layers arrange alternately along the c-axis. The lattice parameters include a and c all as well as the Curie temperature (T_C) all increase gradually with increasing Mn content. A second-ordered phase transitions from the state of ferromagnetic to paramagnetic has been determined around their own T_C of 340, 348 and 351 K for (Mn_0.5Ni_0.5)_63.3Ga_36.7, (Mn_0.5Ni_0.5)₆₅Ga₃₅ and (Mn_0.5Ni_0.5)_66.6Ga_33.4, respectively. Moreover, the MCE performances of (Mn_0.5Ni_0.5)_60+xGa_40-x alloys were determined by the figure merits of the maximum magnetic entropy change (-ΔS_M^max), temperature-averaged entropy change (TEC) with 5 K-lift and refrigerant capacity (RC). The values of -ΔS_M^max, TEC (5), and RC are 3.26 J/kg K, 3.24 J/kg K, and 229.9 J/kg for (Mn_0.5Ni_0.5)_63.3Ga_36.7, 3.72 J/kg K, 3.70 J/kg K and 287.3 J/kg for (Mn_0.5Ni_0.5)₆₅Ga₃₅, as well as 3.56 J/kg K, 3.53 J/kg K and 265.1 J/kg for (Mn_0.5Ni_0.5)_66.6Ga_33.4 under the external applied field change of 0–7 T, respectively.