Magnetization Reversal in Focussed Ion-Beam Implanted YIG Patterns

Magnetization reversal in Bi- and Ga-substituted YIG film rectangular patterns, formed by micro-lapping and subsequent acid etching, is based on the nucleation and extension of reverse domains. As the pattern size is reduced from 300×300 μm to less than 100×100 μm, the nucleation field (H_n) increases from 100 to 530 Oe, equal to the anisotropy field. To control the Hn, an artificial magnetic defect was formed in the center of the pattern by using focussed ion-beam implantation. When Ge- or Si-ions were implanted at 50 keV in a spot 0.3 μm in diameter, the H_n dropped to less than 330 Oe. As the Ge ion-implanted area was extended, the H_n gradually decreased. Assuming that the ion-implanted region is a reverse-domain nucleus, the H_m was calculated as the external field for which the maximum total magnetic energy is attained. Theoretical values of H_m agreed well with experimental ones.