Low-field large magnetostriction in DyCo₂ due to field-induced rearrangement of tetragonal variants

The synchrotron high-energy x-ray diffraction was used to trace directly the structural evolution of polycrystalline DyCo₂, one of RT ₂ (R = rare earth, T = Co, Fe) compounds with Laves phase, as a function of temperature and magnetic field. When the DyCo₂ compound was zero-field cooled down below T_C, the high temperature cubic lattice was distorted into tetragonal structure, associated with an expansion of unit cell volume. It was further found that the large magnetostriction at low magnetic field was due to the preferential rearrangement of tetragonal variants in the low-temperature ferrimagnetic phase. Our finding of the field-driven preferential selection of tetragonal variants in the polycrystalline materials provides important clues for exploring the advanced ferromagnetic alloys with a large magnetostriction at low field.