Ferromagnetic resonance observation of exchange and relaxation effects in CrO₂

Abstract

Ferromagnetic resonance (FMR) was observed in epitaxial thin films of CrO2 grown on TiO2. FMR spectra were taken at 9.5 and 35 GHz and at temperatures from 4 K to above the ordering temperature of 393 K. The spectra of these films are generally complicated because of surface roughness and the distribution of stresses and anisotropies through their thickness. The thinnest films, however, display typical spin wave spectra, which could be approximated using uniform magnetic material analyses. The exchange constant at 300 K, D∼70 me V Å2, is consistent with values derived from the temperature dependence of M at low temperatures. The temperature dependence of D was extracted from the spin wave spacing and is similar to other magnetic metals. Our data indicate a room temperature Gilbert damping parameter of at most 0.0023 near 300 K, which is less than those of metallic magnetic materials except possibly Fe. The small damping parameter suggests that intrinsic losses seen in other magnetic metals, which may arise from electronic transitions between bands of different spin character, are small in CrO2. © 2001 American Institute of Physics.