Mean field theory of anomalous magnetic thermodynamics CrCl3

Abstract

The van der Waals halide CrCl3 hosts long-range magnetic order at low temperatures with ferromagnetic intralayer and antiferromagnetic interlayer alignment. Several experimental studies have recorded two phase transitions, one at 17 K and one at 14 K, which has led to a debate regarding their origin. Another long debated subject is the structural phase transition from monoclinic to rhombohedral ordering upon cooling and whether the crystal is fully trigonally ordered at low temperatures. An incomplete structural phase transition may lead to a two-phase structure with a mixture of rhombohedral and monoclinic layers. This structural heterogeneity, along with weakly interacting layers, causes a departure from single-phase stability. Here, we present a mean-field theory treatment of the magnetic ordering in mixed-phase CrCl3, and we show that the temperature-dependence of the staggered magnetization and heat capacity exhibit anomalous non-monotonic behavior due to these stacking defects. Depending on the layer stacking, phase transitions at 17 K, for monoclinic-type stacking, and at 14 K for rhombohedral-type stacking, occur, and when the crystal has mixed stacking, two phase transitions are found, closely resembling those observed in experiments. These calculations of magnetization and heat capacity provide an interpretation and a guide for magnetometry and calorimetry experiments, while highlighting the sensitivity of the magnetic state with respect to the structure of this layered magnetic system.