Pressure-induced structural phase transition in the ferromagnetic Heusler alloy <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ni</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi>MnGa</mml:mi></mml:mrow></mml:math>
T. Eto, Yuki Nakamoto, Tomoko Kagayama, Yoshiya Adachi, Saori I. Kawaguchi, Naohisa Hirao, Yoshiya Uwatoko, Makoto Nagasako, T. Kanomata
Abstract
The effect of pressure on the crystal structure of ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ was investigated up to 41 GPa using in situ angle-dispersive x-ray diffraction with synchrotron radiation, an imaging plate detector, and a diamond anvil cell. A pressure-induced transition from a cubic $L{2}_{1}$ structure (space group $\mathit{Fm}\overline{3} m$) to a 10-layer modulated monoclinic structure ($C2/m$) with a distortion of $\ensuremath{\beta}\ensuremath{\sim}{92}^{\ensuremath{\circ}}$ occurred at a pressure of 19.1 GPa or lower. The volume change at the martensitic transition is a minute value of about $\ensuremath{-}0.1%$. The bulk modulus for the low-pressure phase is 147(2) GPa, consistent with previous studies. In contrast, the bulk modulus for the high-pressure phase is 229(4) GPa, significantly higher than the former bulk modulus. Initial permeability measurements of the ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ were also conducted at various pressures up to 1 GPa. The pressure dependencies of the Curie temperature, premartensitic, and martensitic transition temperatures are discussed in detail.