Antiphase boundaries in Ni-Mn-Ga single crystal—experiment and model

Thermally induced antiphase boundaries (APBs) in ferromagnetic, ordered Ni-Mn-Ga single crystal exhibit complex, irregular shapes and closed loops without any lattice plane preferences. The APBs were visualized on polished (100) surface using magnetic force microscopy (MFM) at the same location in parent cubic austenite and monoclinic martensite with uniaxial magnetic anisotropy. Based on ab initio calculation, we suggest that one APB curve with dark and light contrast consists of a pair of APB interfaces with narrow, only one-layer thick, core with structural partial B2' order in contrast to full L21 order of bulk. Calculated magnetic contrast using magnetostatic continuum simulations agrees well with MFM observation.