Exchange anisotropy in Cu-Mn-Al alloy

The 44.7Cu-20.6Mn-34.7Al(at. %) alloy in the composition range between the Heusler phase and the κ phase exhibits remarkably constricted hysteresis loops and high coercive force after annealing at about 300 °C. It has been found that this alloy shows displaced hysteresis loops at room temperature when cooled down from 350 °C in a magnetic field and that the hysteresis loops shift along the magnetization axis, not along the field axis, when the alloy is cooled to 77 K in a magnetic field. Broad rounded maxima of magnetization are observed at about 250 °C for the sample quenched from 380 °C in thermomagnetic measurements. The characteristics of the magnetic behavior are similar to those reported for mictomagnetic alloys, e.g., Cu-Mn alloys. The high coercive forces and the displaced and constricted hysteresis loops observed in the 44.7Cu-20.6Mn-34.7Al alloy are supposed to be attributed to the exchange anisotropy interactions between the ferromagnetic domains of the Heusler phase and the antiferromagnetic Mn-rich domains.