Full-replica-symmetry-breaking spin glass in the random Blume-Capel model

We realize the full-replica-symmetry-breaking scheme by Parisi to obtain low-temperature entropy and specific heat for the spin-glass phase, which is predicted by the random Blume-Capel model. This theory describes special features of spin-glass behavior in a series of ${\mathrm{Fe}}_{x}{\mathrm{TaS}}_{2}({\mathrm{Se}}_{2})$ compounds, in which the intercalated ${\mathrm{Fe}}^{2+}$ ions can lose their magnetic moments due to a transition to a low-spin singlet state. We demonstrate that the magnetic moment loss-recovery process by iron ions and the nonstoichiometry caused by their different crystallographic positions significantly affect the shape of the temperature dependence of the entropy and the specific heat near the tricritical point of the transition to the singlet paramagnetic state. Ways to enhance nonstoichiometry in these materials are discussed to validate the theory.