Magnetic and Magneto-Transport Properties of Nickel-Rich Ni-Mn-Ga Heusler Alloys

摘要

Electrical resistivity, p of nickel-rich Ni_(2+x)VIn_(1_x)Ga has been measured up to a magnetic field of 8T and within a temperature range from 4.2 to 300 K. At lower temperatures (4.2-70 K), thermal variation of p(T) follows a combination of -T~(1/2) dependent term coming from electron-electron interaction and BT~2 term due to s-d interaction. At higher temperature region (up to ~280 K), p(T) is interpreted in terms of electron-phonon and s-d interaction. A substantial jump in resistivity has been observed while the martensitic transformation takes place. A high negative magnetoresistance (～8%) has been observed at room temperature due to a change of 8T magnetic field for the sample Ni_(2.208)Mn_(0.737)Ga, where martensite-austenite structural and ferrc-para magnetic transition temperatures almost coincide with each other. Magnetic properties of those samples have also been studied to understand their anomalous change in magnetic entropy and magnetoresistance.