Annealing of Magnetic Properties of Ion Implanted Garnet Epitaxial Films

Abstract

Annealing characteristics are reported for two epitaxial garnet materials: ${\mathrm{Y}}_1{\mathrm{Eu}}_{\text{1.85}}{\mathrm{Yb}}_{\text{.15}}{\mathrm{Al}}_{\text{1.1}}{\mathrm{Fe}}_{\text{3.9}}{\mathrm{O}}_{12}$ and ${\mathrm{YGdTmGa}}_{\text{.8}}{\mathrm{Fe}}_{\text{4.2}}{\mathrm{O}}_{12}$ on (111) ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ . Ion implantation has been used to suppress hard bubbles in these materials. The changes observed in the magnetic properties during annealing are due to removal of the ion implantation effects, removal of growth induced anisotropy and changes in the magnetization, 4πM_s. The films used were ∼6μm thick and supported ∼6μm bubbles at room temperature. Three parameters were measured after 30 minute anneals in O₂: the minimum bias field H_m for bubble collapse, the bias field collapse range ΔH, and the demagnetized domain strip width, from which 4πM_s, the material length ℓ, and the domain wall energy σ_w were determined. Hydrogen ion implantation at 25–50 keV typically increases H_m by several oersteds and decreases ΔH from ∼25–40 Oe down to ∼1 Oe. Annealing of the ion implantation effects was observed in the range 600 to 1000°C. The implantation‐induced increase in H_m disappeared at about 800°C and ΔH increased abruptly to ∼20–25 Oe at temperatures ranging from 700 to 850°C for the particular materials and implantation conditions used. Annealing at temperatures >800°C causes a redistribution of the Al or Ga atoms between tetrahedral and octahedral sites causing changes in 4πM_s. Annealing at ∼1200°C also causes a reduction in growth induced anisotropy by randomizing the distribution of the different rare earth atoms on the dodecahedral lattice sites.