Using Kerr Microscopy for Direct Observation of Magnetic Domains in Ni–Mn–Ga Magnetic Shape Memory Alloy

Giant magnetic-field-induced strain up to 12% in Ni–Mn–Ga single crystal is due to magnetically-induced reorientation of the twinned martensitic low symmetry crystal structure. An important interplay is arising from the interaction between ferroelastic domains (twin domains) and magnetic domains. Here, we studied the magnetic domains in an Ni50Mn28Ga22 single crystal exhibiting 6% strain by using a magneto-optical indicator film and for the first time also directly by the Kerr magneto-optical microscopy. To compare the magnetization behavior of bulk and surface, we measured the magnetization loops by the Kerr effect (MOKE) and by the vibrating sample magnetometry. We demonstrate that using a particular arrangement of the Kerr microscopy enables visualizing the magnetic domains structure and its evolution in the magnetic field.