Lorentz Force Microscopy of Magnetic Domains in Ni-Mn-Ga

The magnetic shape memory alloy Ni-Mn-Ga is of great interest for its properties of large magneticfield- induced strain. This induced strain is a result of twin boundary movement caused by magnetic anisotropy energy. Magnetic shape memory alloys have magnetic and crystallographic domains. While crystallographic domains can be imaged by conventional diffraction contrast, magnetic domains are invisible by standard microscopy. The Boise State Center for Materials Characterization (BSCMC) is equipped with a JEOL JEM 2100 HR transmission electron microscope with a magnetic field cancellation system unique in the USA. This instrument is one of only a few in the world that is capable of imaging magnetic domains. Initial results show worm-like magnetic domains within twin crystallographic domains. The size of the magnetic domains is typically 150 nm