Phase Transformations and the Magnetocaloric Effect in Heusler Alloys of the Family Ni_{51 – x}Mn_33.4In_15.6V_x

The work is devoted to the study of the dependence of the structure, magnetic properties, and functional properties such as shape memory effect (SME) and magneto caloric effect (MCE) of Heusler alloys of the Ni_{51 – x}Mn_33.4In_15.6V_x family on the degree of vanadium doping x. Studies using scanning electron microscope (SEM), differential scanning calorimetry (DSC) and magnetometry revealed in all studied samples of Heusler Ni_{51 – x}Mn_33.4In_15.6V_x alloys the presence of a Curie point type magnetic phase transition (PT) and a metamagnetostructural phase transition (MMSPT), of the first order which is accompanied by a sharp decrease in magnetization in the low-temperature martensitic phase. The temperature of the magnetic PT is weakly dependent on x, the temperature of the MMSPT decreases with increasing x. The temperature of the MMSPT is very sensitive to the magnetic field. For the Ni₅₀Mn_33.4In_15.6V₁ sample, the sensitivity is—5 K/T. Direct measurements of the MCE in alternating magnetic fields of 0.62 and 1.2 T showed the presence of a direct MCE at the point of magnetic PT and an inverse MCE at the point of MMSPT. There is a strong decrease in the MCE with an increase in the frequency of the alternating magnetic field from 1 to 30 Hz both near the magnetic PT and near the MMSPT. Measurements of the dependence of bending deformation on load and temperature have shown that all studied alloys exhibit SME near MMSPT. It can be concluded that due to the combination of high sensitivity of MMSPT to the field and SME, this family of alloys is promising for the creation of magnetically controlled actuators.