Evidence for preferential rearrangements of martensite variants by magnetic field in antiferromagnetic CoO crystal

The synchrotron high-energy x-ray diffraction provides the direct crystallographic evidence for the magnetic-field-driven preferential rearrangements of martensite multivariants in antiferromagnetic CoO crystal. When a magnetic field was incrementally applied up to 6 T on the CoO single crystal cooled below the Ńel temperature, the martensite variants with the magnetization easy-axis parallel to the magnetic field direction (H) were consumed, while the variants with magnetic moments perpendicular to H were enhanced. The microscopic origin for the observation is discussed, which provides important information for understanding the magnetic-field-driven strain observed in the antiferromagnetic alloys, with a selection principle on martensite variants different from that found in the ferromagnetic shape memory alloys.