Magnetostructural transition and magnetocaloric effect inNi55Mn20Ga25single crystals

Abstract

A first order transition from a paramagnetic-austenite phase to a ferromagnetic-martensite phase occurring in off-stoichiometry single crystals of ${\mathrm{Ni}}_2\mathrm{Mn}\mathrm{Ga}$ at 313 K presents unique features due to the multifunctional character of the magnetic shape memory alloy. A remarkable magnetocaloric effect, associated with an entropy change up to $\Delta S\approx -86\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ and an adiabatic temperature change $\Delta T\approx 2.2\mathrm{K}$, accompanied by mechanical strain $\Delta \epsilon ⩾3\%$ have been observed in samples subjected to changes of the applied magnetic field $\Delta H=4\times {10}^6\mathrm{A}∕\mathrm{m}(\approx 5\mathrm{T})$. The effects of magnetic field, temperature, and stress on the entropy variation $\Delta S$ are quantified and compared.