Crossover from classical to quantum regime in Ce-lattice systems

Abstract

Different types of magnetic phase diagrams are analyzed with the scope to detect signs of a crossover between the classical (thermal fluctuations) regime and the critical (quantum fluctuations) one. In systems where TN,C is driven down to the mK range by alloying Ce-ligands (x), clear changes in the magnetic phase are observed once TN,Co<2 K. On the contrary, when TN vanishes at finite temperature (driven by pressure or x) the phase boundaries do not reach temperatures lower than ≈3K. In a third type of phase diagrams, characterized by a weak TN(x, p) dependence, signs of phase separation are suspected. Distinctive properties of each mentioned group are recognized and some exemplary cases analyzed in detail. Those properties coincide indicating a crossover temperature slightly above 2 K.