In this work, magnetic and magnetocaloric properties of a new ${\rm{Mn_{27}Cr_{7}Ni_{33}Ge_{25}Si_{8}}}$ high entropy alloy (HEA) are investigated. The crystal structure is characterised through multiphase Rietveld refinement of X-ray diffraction data. The structure of the HEA was found to be the orthorhombic structure in the Pnma space group. The result obtained from the Arrott plot indicates that the ferromagnetic-paramagnetic phase transition of the sample is the second order. The maximum magnetic entropy change is obtained with the value of 2.49 Jkg-1K-1 among the high entropy alloys which is not contain rare earth elements reported so far.

The magnetocaloric and magnetoresistance properties of amorphous Co-based (Co_0.402Fe_0.201Ni_0.067B_0.227Si_0.053Nb_0.05)_100−xCu_x (x = 0, 0.5, 0.75 and 1) ribbons were investigated. Cu additions changed the crystallisation temperature (T_x) and the Curie temperature (T_C). The saturation magnetisation (M_s) and coercivity (H_c) for alloys were in the range of 65.51–38.49 emu/g and 1.99–6.84 A/m, respectively. Under an applied magnetic field change of 2.2 T, the (−ΔS_M)^max for (Co_0.402Fe_0.201Ni_0.067B_0.227Si_0.053Nb_0.05)_100−xCu_x with x = 0, 0.5, 0.75 and 1 are 0.77, 0.71, 0.89 and 0.67 Jkg⁻¹ K⁻¹, respectively. The values of refrigeration capacity (RC) for the as-spun glassy alloys are comparable with those of previously studied Fe-based metallic glasses such as Fe₈₀B₁₀Zr₉Cu₁, (Fe_0.76B_0.24)₉₆Nb₄ and Fe₈₂Ni₂Zr₆B₁₀. In addition, the maximum magnetoresistance (MR) values for (Co_0.402Fe_0.201Ni_0.067B_0.227Si_0.053Nb_0.05)_100−xCu_x with x = 0, 0.5, 0.75 and 1 are found to be 110, 38, 23 and 1% around the Curie temperatures under an applied magnetic field change of 1 T, respectively. With good RC, negligible hysteresis due to very low coercivity values and large magnetoresistance, these Co-based amorphous alloys can be used as the high temperature magnetic refrigerants and multifunctional applications working in the temperature range of 450–600 K.

The impacts of adding Cr on the Curie temperature (T_C), glass-forming ability (GFA), and magnetocaloric effect were studied in Fe_68−xCr_xTb₅B₂₃Nb₄ (x = 0, 2, 4, 6 and 8) metallic glasses prepared by suction casting. GFA depends on Cr content in the composition. For Fe_68−xCr_xTb₅B₂₃Nb₄ bulk metallic glasses (BMGs), with critical diameters up to ~3 mm can be produced by suction casting and maximum value of GFA was found for x = 6. By exchanging Cr with Fe partially, T_C could effectively be adjusted in a quite broad temperature interval from 487 K for x = 0 to 267 K for x = 8, whereas maximum magnetic entropy change decreased from 1.16 to 0.53 Jkg⁻¹ K⁻¹ and refrigeration capacity (RC) changed from 116 to 45.05 J/kg under a low field change of 2 T. Though T_C is shifted to room temperature, maximum magnetic entropy change and RC decreased almost half of the base alloy. To enhance these properties (Fe_0.62Cr_0.06Tb_0.05B_0.23Nb_0.04)_100−yCu_y (y = 0.75, 1), metallic glasses are prepared. By the help of small addition of Cu, magnetocaloric properties can be effectively increased without changing the T_C. These findings show that the successful synthesis of the Fe-based Fe₆₂Cr₆Tb₅B₂₃Nb₄ and (Fe_0.62Cr_0.06Tb_0.05B_0.23Nb_0.04)_100−yCu_y (y = 0.75, 1) BMGs near room temperature, could be considered as promising candidates as magnetic refrigerant materials.