The Study Of Magnetostructural Transition And Magnetoresponsive Effects On MnMX And NiMn-based Alloys

Magnetic alloys,which experience the magnetic-field-induced phase transition,have attracted considerable attention for the accompanied multi-magnetoresponsive effects in their potential application in sensor,actuator and magnetic cooling refrigerator.Recently,large magnetostrictive and magnetocaloric effects have been found in some compounds with first-order transition,such as Ni-Mn based magnetic shape memory alloys and MM'X?M=Mn,M'=Co or Ni,X=Si or Ge?alloys.However,there are also some drawbacks,such as irreversibility,large hysteresis,poor mechanical property and low transition temperature.In this study,we investigate the magnetic-field induced phase transition in some groups of Mn-based alloys and improve the properties by tuning content and doping different metal element.We choose MnNiGe alloy as the research object,using V to replace Ni to increase the Mn-Mn separation,and the ferromagnetic coupling is obtained near room temperature.With the increasing content of V,the transition decreases and a temperature region as large as 130 K is established.The value of magnetic entropy change in MnNi_0.88GeV_0.12 alloy is 15.057 J·kg^-1·K^-1 with?B=5 T,while the value of refrigerate capability reaches 33.44 J/kg.Meanwhile,virgin effect in MnMX alloys has been studied.Virgin effect obviously exists in compact samples,but is nearly absent in the samples with defects structure.We infer that the origin of virgin effect is the large stress caused by giant lattice-parameter change during the structural transformation,while the cracks in defective alloys are helpful to release the stress and thus eliminate the virgin effect.Since the structural transformation in MnMX alloys is always accompanied by large lattice-parameter change,it can be concluded that virgin effect is a common phenomenon in compact MnMX alloys.Decreasing the hysteresis is the only way to improve the reversibility of magnetoresponsive effects in Ni-Mn based alloys.In our study,a low hysteresis?4 K?has been obtained in Ni₅₀CuMn_33.4In_15.6 alloy,and transition temperature maintains near room temperature.Compared with large hysteresis alloys,it is demonstrated that low hysteresis benefits for the recoverability of magnetostructural transition.