Magnetization Curves of Fe–Ni (50–50) Single Crystals Ordered by Neutron Irradiation with an Applied Magnetic Field

Spherical Fe–Ni (50–50) single crystals were ordered by neutron irradiation at 295°C in the presence of a magnetic field. Magnetization curves and magnetic anisotropy energy measurements demonstrate the very important directional effect of the irradiation magnetic field on the bulk anisotropy of the single crystal. When the magnetic field is applied along a fourfold axis, the bulk magnetic anisotropy is tetragonal with a very large value for K3. When the magnetic field is applied along a three fold axis, the bulk magnetic anisotropy is cubic and the threefold axis becomes an easy axis of magnetization; the magnetization measured along the easy direction reaches saturation with a certain law of approach, while the magnetization measured along the [100] direction reaches saturation immediately. The model proposed by Néel, in which three types of quadratic ordered domains are assumed to be strongly coupled, fits well the experimental results. An electron microscopy image shows the different type of ordered domains and the superlattice spots.