COMPOSITIONAL DEPENDENCE OF MAGNETIC ENTROPY CHANGE IN Ni_(2+x)Mn_(1-x)Ga WITH COUPLED MAGNETOSTRUCTURAL PHASE TRANSITION

摘要

We report on magnetocaloric properties of Ni_(2+x)Mn_(1-x)Ga undergoing a first-order phaserntransition from ferromagnetic martensite to paramagnetic austenite. Experimental resultsrnobtained revealed that magnetic entropy change ΔSM calculated from isothermal magnetizationrncurves is largest in the alloys with x = 0.18 – 0.20. ΔSM in the alloys with a higher Ni excess wasrnfound to be considerably smaller. Direct measurements of the adiabatic temperature change ΔTrnin these alloys revealed similar tendency. The observed experimental results are attributed to thernfact that with increasing Ni excess x, simultaneous decrease in magnetization saturation and inrnthe lattice entropy change at martensitic transformation temperature is observed.