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

Electrical resistivity, ρ of nickel-rich Ni2+xMn1-xGa has been measured up to a magnetic field of 8 T and within a temperature range from 4.2 to 300 K. At lower temperatures (4.2–70 K), thermal variation of ρ(T) follows a combination of -√T dependent term coming from electron–electron interaction and BT2 term due to s–d interaction. At higher temperature region (up to ∼280 K), ρ(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 8 T magnetic field for the sample Ni2.208Mn0.737Ga, where martensite–austenite structural and ferro–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.

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