Molecular-field-model calculations of magnetic bubble LPE garnet film properties

By using a simple thermodynamic model combined with the molecular field model, we have determined from previously published experimental results that the most consistent enthalpy of exchange for Ga³⁺between tetrahedral and octahedral sites in epitaxial iron garnet films is -5000 cal/mole (-0.22 eV). The molecular field model is also used in calculating Curie temperatures and in calculating the temperature dependence of the material length parameter for LPE garnet films. An expression is presented relating the Curie temperature to the molecular field coefficients for a three magnetic sublattice system. By using a two magnetic sublattice system, the calculations of the temperature dependence of the material length parameter (l) show that a composition containing ∼0.2 octahedral substitution and ∼1.1 tetrahedral substitution should show a low (\Deltal/l\DeltaT)0-25°C. A film of approximate composition [Y1.9Ca1.1][Fe1.8Sc0.2] (Fe1.9Ge1.1)O12was grown by LPE. The temperature dependence oflwas found to be -0.057 percent per degree, which is in good agreement with the predicted value.