Relaxation of rare earth and cobalt ions in polycrystalline yttrium iron garnet

Relaxation at room temperature of rare earths and cobalt ions in ferrimagnetic garnets has been studied by measuring the three linewidths : ΔH, resonance linewidth, Δ Heff, effective linewidth, ΔHK, spinwave linewidth. These linewidths have been measured at 9 GHz Δ Heff, far from resonance, Δ Hkin perpendicular and in parallel pumps. From experimental results, relations between ΔH, Δ Heffand Δ Hkhave been found which are in good agreement with the theory. The broadening δ (ΔH), due to the introduction of rare earths ions, allows the relaxation time τ (about 10^-13sec) of some rare earths ions to be deduced from Kittel´s theory. At room temperature, this theory explains the gyromagnetic properties of Sm³⁺, Tb³⁺, Dy³⁺, Ho³⁺and Er³⁺ions. An adaptation of this theory allows us to explain also the behaviour of Gd³⁺ions. Relation between δ (ΔH) and the saturation magnetization 4π Msare explained for the Sm, Dy, Ho and Er ions by an extension of Kittel´s theory, but this explanation is not unique.