Magnetocaloric Effect with Very Small Magnetic Hysteresis Losses of CoMn_1−x Ti _x Ge Alloys

The effects of Ti substitution for Mn and heat treatment on structural, magnetic, and magnetocaloric properties of CoMnGe alloy have been investigated using electron microscopy, X-ray diffraction, calorimetric, and magnetic measurements. According to X-ray diffraction measurements, CoMn_1−x Ti _x Ge alloys are in a single phase hexagonal structure at room temperature. It is found that the as-cast CoMn_0.95Ti_0.05Ge alloy shows a magnetostructural phase transition close to room temperature. The transition shows a large magnetic entropy change and a small hysteresis in the isothermal magnetic field-dependent magnetization measurements. After annealing, the phase transition temperature decreases slightly and the magnetization is sharply decreasing at Curie temperature. The sharp change of magnetization at phase transition temperature is accompanied by a significant increase in the magnetic entropy change, i.e., magnetic entropy change value for the magnetic field change of 1 T was increased from −3.3 to −6.3 J kg⁻¹ K⁻¹. Moreover, after annealing, hysteresis losses reduced significantly for ∆H = 7 T. Accordingly, the heat treatment has a significant effect on magnetocaloric properties of the CoMn_0.95Ti_0.05Ge alloy.