Effect of Mo and Cr substitution on electrical and magnetic propertions of NiMnSb shape memory alloys system

In this study, Mo and Cr replaced Ni in Ni-Mn based Heusler alloys and the structural, electrical and magnetic properties of the produced samples were investigated. Firstly, Ni50-xMoxMn37Sb13 (x=0,1,3,5 ve 7) and Ni50-yCryMn37Sb13 (y=0,3,5 ve 7) ferromagnetic (FM) shape memory alloys were produced in ingot form by arc-melting method order to obtain the desired crystal structure, the samples were heat treated at 870 oC for 24 hours and then cooled in ice water. XRD analysis was performed to examine the crystal structure. It was determined that x=0, x=1 and y=3 samples were in Martensite phase at room temperature. On the other hand, it was determined that the other samples were in the cubic L21 phase, which indicates the presence of austenite phase. EDX analysis shows that B doping is successful in preventing Mn evaporation. Low-field M-T analysis revealed that the samples exhibited premartertensitic phase transformation. M-T curves measured at 1 T magnetic field demonstrated that the materials exhibited Martensitic structural phase transformation The phase transition temperatures decreased with increasing the amount of both Mo and Cr in accordance with the e/a rule. In addition, increasing the doping amount increased the magnetization of the samples. The ρ-T curves performed without magnetic field and under 1 T magnetic field confirmed that the samples exhibited Martensitic transformation. The phase transition temperatures decreased with the application of magnetic field. The resistivity of the samples gradually decreased with Mo and Cr doping. In order to investigate the presence of antiferromagnetic (AFM) interactions at low temperatures, M-H analyzes at 5 K of the cooled samples with and without field were performed. The results obtained show that AFM and FM coexist at low temperatures. Here, the shift of the origin of the M-H curves was attributed to the Exchange Bias effect. Arrott-Plot curves were used to determine the type of phase transition. At temperatures in the As-Af range, especially at low magnetic field values, negatively sloped curves were obtained due to the first-order structural transition. Magnetic entropy (∆SM) values were calculated using Maxwell's equations and data from M-H analyses measured at different temperatures. In order to determine the effectiveness of magnetic cooling, cooling capacity (RC), hysteresis loss (HL) and effective cooling capacity (RCeff) values were calculated as well as ∆SM. For Mo doped samples, the highest ∆SM and RCeff values were obtained in the x=3 sample with 2.70 J/kgK and 19.95 J/kg, respectively. For Cr doped samples, the highest ∆SM (4.46 J/kgK) and RCeff (13.53 J/kg) values were obtained in the y=5 sample.