Cross-relaxation and phonon bottleneck effects on magnetization dynamics inLiYF4:Ho3+

Abstract

Frequency and dc magnetic field dependences of dynamic susceptibility in diluted paramagnets $\mathrm{Li}\mathrm{Y}{\mathrm{F}}_{4}:{\mathrm{Ho}}^{3+}$ have been measured at liquid helium temperatures in ac and dc magnetic fields parallel to the symmetry axis of a tetragonal crystal lattice. Experimental data are analyzed in the framework of the microscopic theory of relaxation rates in the manifold of 24 electron-nuclear sublevels of the lowest non-Kramers doublet and the first excited singlet in the ${\mathrm{Ho}}^{3+}$ ground multiplet $^{5}I_{8}$ split by the crystal field of ${S}_{4}$ symmetry. The one-phonon transition probabilities were computed using electron-phonon coupling constants calculated in the framework of the exchange charge model and were checked by optical piezospectroscopic measurements. The specific features observed in field dependences of the in- and out-of-phase susceptibilities (humps and dips, respectively) at the crossings (anticrossings) of the electron-nuclear sublevels are well reproduced by simulations when the phonon bottleneck effect and the cross-spin relaxation are taken into account.