Relaxation rates of magnetization in LiYF4:Ho3+ crystals

Theory of magnetization relaxation in a diluted paramagnet based on calculations of relaxation rates due to electron-phonon coupling and magnetic dipole-dipole interactions is developed. Assuming fast establishment of equilibrium in the spin system and the Gaussian line shape for the spectral density of the dipole-dipole reservoir, we have derived a master equation for a paramagnetic ion. The developed approach is used to interpret dynamic magnetic measurements in LiYF4:Ho3+ single crystals. We show specific variations of low temperature magnetization dynamics at the magnetic field values corresponding to (anti-)crossings of electron-nuclear sublevels of the Ho3+ ground state. The measured dependences of the ac-susceptibility on frequency, holmium concentration and the applied magnetic field are described when taking into account the phonon bottleneck effect and the cross-relaxation. Evolution of the magnetization of the LiYF4:Ho3+ in the reversed field is considered. © 2007 Elsevier B.V. All rights reserved