Low-temperature properties of the dilute dipolar magnet LiHoxY(1-x)F4
Abstract
We analyze recent experiments on the dilute rare-earth compound LiHoxY(1-x)F4 in the context of an effective Ising dipolar model. Using a Monte Carlo method we calculate the low-temperature behavior of the specific heat and linear susceptibility, and compare our results to measurements. In our model the susceptibility follows a Curie-Weiss law at high temperature, chi ~ 1/(T-Tcw), with a Curie-Weiss temperature that scales with dilution, Tcw ~ x, consistent with early experiments. We also find that the peak in the specific heat scales linearly with dilution, Cmax(T) ~ x, in disagreement with recent experiments. Experimental studies do not reach a consensus on the functional form of these quantities, and in particular we do not see reported scalings of the form chi ~ T-0.75 and chi ~ exp(-T/T0). Furthermore we calculate the ground state magnetization as a function of dilution, and re-examine the phase diagram around the critical dilution xc=0.24(3). We find that the spin glass susceptibility for the Ising model does not diverge below xc, while recent experiments give strong evidence for a stable spin-glass phase in LiHo0.167Y0.833F4.