Study of structural, magnetic, and magnetocaloric properties of Ho 1− x Ca x MnO 3

The structural, magnetic, and magnetocaloric properties of Ho 1− x Ca x MnO 3 ( x = 0, 0.1, 0.2, and 0.3) manganites were investigated in depth in this work. The samples were made by using standard solid-state reaction. The calcium-doped samples are formed in orthorhombic crystal structure with Pnma space group, while undoped sample shows hexagonal crystal structure with P63cm space group according to room temperature XRD measurements and Rietveld refinement by using the TOPAS software. The field emission scanning electron microscopy (FESEM) was used to examine the microstructure, and an energy-dispersive X-ray diffractometer (EDX) was used to estimate chemical compositions. At the Curie temperature, all the samples show a second-order magnetic phase transition. It has been discovered that when the amount of calcium doping increases, the Curie temperature increases. The effective magnetic moments (μ eff ) of HoMnO 3 , Ho 0.9 Ca 0.1 MnO 3 , Ho 0.8 Ca 0.2 MnO 3 , and Ho 0.7 Ca 0.3 MnO 3 are 10.71, 10.93, 11.17, and 11.54 μB, respectively, which are equivalent to the theoretical value of 11.45 μB. The magnetic entropy change (− ΔS M ) was calculated by using isothermal magnetization versus applied magnetic field. The calculated − ΔS M = 8.9 Jkg −1 K −1 value for undoped HoMnO 3 sample at 17.7 K, while with an increase in calcium doping, the − ΔS M value have been drop down from 3.3 to 2.2 Jkg −1 K −1 about 35 K temperature.