Evidence for a gap in the excitation spectrum of CrO2

Magnetization and resistivity of CrO2 powders and oriented CrO2 films on di fferent TiO2 single-crystal substrates are reported, and the low-temperatur e specific heat is measured on powders. The M(T) data follow a Bloch T-3/2 law, with no sign of a spin-wave gap. The residual resistivity depends stro ngly on film texture, but a T-2 temperature dependence of the resistivity i s found in all samples above a cut-off temperature of the order of 70 K. Th e behavior is attributed to electron-magnon spin-Rip scattering which is su ppressed at low temperature in a half-metallic ferromagnet. (C) 1998 Americ an Institute of Physics.