Magnetic-field-induced decomposition in Cu₂MnAl Heusler alloys

A magnetic field enhanced the decomposition of a Cu₂MnAl Heusler alloy. An aging treatment at 573 K under 10 T promoted decomposition of a L2₁ phase and hard magnetic properties were exhibited. The crystallite size of the L2₁ phase decreased on annealing over 12 h and approached 22 nm at zero field. However, the crystallite size of the L2₁ phase of the 5 T-annealed sample was almost half that of the 0-T-annealed sample and decreased rapidly, indicating enhanced grain refinement by in-field annealing. Decomposition of the L2₁ phase was more pronounced in the 10-T-aged sample. The hysteresis loop for 10-T-aged sample had a large coercive force of 232 mT and a magnetization of 13 Am²/kg. These properties were markedly different from those of the 0-T-annealed sample. An increase of nucleation owing to a decrease of critical radius caused grain refinement associated with decomposition and magnetic hardening of Cu₂MnAl.