Observation of magnetic domain evolution in constrained epitaxial Ni–Mn–Ga thin films on MgO(0 0 1) substrate

Abstract

• The evolutions of the magnetic domain of a typical epitaxial Ni–Mn–Ga thin film were investigated through wide-field magneto-optical Kerr-microscopy. • The abrupt magnetization changes in the hysteresis loops can be observed in the Type-Y area with the applied magentic field parallel to the twin interfaces. • The abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the magnetically induced variant reorientation. Epitaxial Ni–Mn–Ga thin films have promising application potential in micro-electro-mechanical sensing and actuation systems. To date, large abrupt magnetization changes have been observed in some epitaxial Ni–Mn–Ga thin films, but their origin - either from magnetically induced martensite variant reorientation (MIR) or magnetic domain evolution - has been discussed controversially. In the present work, we investigated the evolutions of the magnetic domain and microstructure of a typical epitaxial Ni–Mn–Ga thin film through wide-field magneto-optical Kerr-microscopy. It is demonstrated that the abrupt magnetization changes in the hysteresis loops should be attributed to the magnetic domain evolution instead of the MIR.