Growth-induced anisotropy arising from ordering of transition metal ions in garnets (invited)

Abstract

The earlier study of the growth-induced anistropy (Ku) in epitaxial YIG produced by the preferential occupation of Ir4+ on octahedral sites has been extended to include most of the transition elements that have degenerate ground states and that can be incorporated in the garnet lattice with the appropriate valence states. Among the 3d elements only Co2+ meets these requirements. For Co2+ charge compensated by Zr4+, Ku increases linearly with the Co/Fe ratio in the melt, reaching 2×105 ergs/cm3 in (111) films for a Co/Fe atomic ratio of 0.17. Among the possible 4d and 5d ions only Ru, Mo, and W are expected to be stable in the desired valence state. Ruthenium yields a large in-plane growth-induced anisotropy (Ku = −1.2×105). Lattice constant, SEM and optical studies indicate that Mo and W have negligible solubility in YIG. For as-grown bubble samples the coercive force (Hc) increase linearly with Ir content, as does Ku. For Ku = 2.3×105, Hc = 70 Oe. The increase of Hc with Ru concentration is substantially smaller. For Ku = −1.2×105, Hc = 2.5 Oe. For YIG (Ir, Ca) samples annealed to reduce Ku (initially 3.5×105) to zero, Hc is 3 Oe, indicating that Ir content alone does not cause the large coercive force. However to data we have not been able to produce an Ir containing material with an easy axis normal and a low value of Hc.