Lead in holmium iron garnet films grown from fluxed melts by liquid phase epitaxy

Abstract

The incorporation of Pb, from the flux, into Ho 3Fe 5O 12 garnet films grown by LPE onto GGC substrates oriented (111) is studied by electron microprobe analysis (EMPA). Results support earlier findings that Pb increases significantly with decreasing growth temperature and that Pb increases, to a lesser degree, with increasing growth rate, induced by axial substrate rotation, at a fixed temperature. Also Pt, from the Pt crucibles which hold the growth melts, increases with Pb, but not in sufficient amounts to completely charge compensate Pb by a compensated ion pair such as Pb 2+-Pt 4+. Angle-lapped films examined by EMPA generally show an increase in Pb in the film region at the substrate interface and a decrease in Pb at the film surface compared to the bulk of the film interior. The increase of Pb at the substrate interface is at least in part a consequence of PbO vapor condensing on the substrate prior to growth. From the standpoint of crystallographic site occupancy, the Pb and Pt pair with Ho and Fe respectively such that comparing the number of Ho + Pb ions with the Fe + Pt ions per formula unit indicates a slight excess of the former over the latter, greater than the expected 3 : 5 stoichiometric ratio. Lattice mismatch results are also discussed and Pb is seen to have less effect upon mismatch than that expected from the radius ratio effect of Pb 2+ substituting for Ho 3+.