Coercivity of epitaxial magnetic garnet crystals

Epitaxial magnetic garnet films of Ga and Ca-Ge substituted YIG grown for bubble memory applications are thought to be the most perfect magnetic materials. However, in spite of their very low dislocation and surface defect densities (≤5 cm²) the coercivity Hcis of the order of 10^-1Oe. This paper reviews the role of various mechanisms in determining static Hcof stripe domains in epitaxial garnet crystals. Statistical fluctuations of material parameters, dislocations and localized surface defects are shown to give a negligible contribution to Hc. The surface roughness of the free surface and stresses inside the transient layer at the substrate/epitaxy interface may cause Hcfrom 0.1 up to some Oe. From the temperature dependence of Hca high density (10¹⁴to 10¹⁶/cm³) of micro-defects was deduced. Transmission electron microscopy revealed the existence of such precipitates responsible for the observed Hcof device quality epitaxial garnets.