Effect of growth atmosphere on rare-earth iron garnets grown from PbO-based fluxes

Abstract

The growth atmosphere over a PbO fluxed melt can significantly affect the platinum and lead concentrations and the magnetic properties of rare-earth iron garnet films grown from that melt. We have investigated this effect using the simple composition (Gd2.5Eu0.5Fe5O12. The films were grown in N2, air, and O2 atmosphere on (111) MgCaZr substituted GGG substrates (substrate lattice parameter a0=12.497 Å) by conventional liquid-phase-epitaxy techniques from PbO and PbO/B2O3 fluxes. Lead is incorporated self-compensatingly from the flux as Pb2+ and Pb4+. The oxygen partial pressure of the growth atmosphere affects the platinum incorporation in the film through the equilibrium between neutral elemental Pt0 and ionic Pt4+ species in the melt. Incorporation of elemental species such as Pt0 in the film is unfavorable, but oxidized Pt4+ ions are accommodated in the lattice in concentrations that depend on their melt concentrations and distribution coefficients. Lead and platinum concentrations were determined by x-ray fluorescence. The incorporation of lead and platinum increased the lattice parameter and the index of refraction of these garnets. The diamagnetic octahedral substitution of Pt had a predictable effect on the magnetic properties, increasing the saturation magnetization and decreasing the Curie temperature, cubic anisotropy, and gyromagnetic ratio. Least-squares analysis and annealing studies showed that lead makes a positive contribution to the growth-induced anisotropy that seems to depend only on the concentration of the Pb2+ species. Platinum incorporation causes a negative contribution to the growth-induced anisotropy that can be annealed out at temperatures of 850–950 °C.