Thulium has been substituted for yttrium in melts for the growth of (Y,Sm,Lu,Ca)3(Fe,Ge)5O12epitaxial garnet films for the purpose of reducing the magnitude of the temperature coefficient &agr;bcof the bubble collapse field. As an extension of previous substitutions [J. E. Davies, G. Galli, and J. C. Suits, J. Appl. Phys. 49, 1859 (1978)] of Tm for Lu to smaller bubble diameters, growth conditions were adjusted to produce films of nearly identical thickness (1.40 &mgr;m) and characteristic length (0.222 &mgr;m at 25°C) for Tm substitutions up to 0.25 atoms in the formula unit. This substitution was found to decrease the magnitude of &agr;bcas measured at 50°C by approximately 0.04%/°C⋅Tm atom. Anisotropy remains nearly constant with Tm substitution.