Influence of metamagnetic phase transitions on thermodynamics of frustrated systems with octahedral structure

Abstract

Common effects of the geometric frustration and of the metamagnetic phase transitions on the thermodynamic properties of antiferromagnetic systems with the octahedral structure are investigated using an exactly solvable antiferromagnetic model on the octahedral recursive lattice. The residual entropies of all ground states are determined and the existence of two highly macroscopically generated single-point ground states with nonzero residual entropies is shown. The first-order character of the metamagnetic phase transitions of the model is demonstrated by discontinuous behavior of the entropy. The presence of the anomalous Schottky-type behavior of the specific heat capacity, i.e., the appearance of an additional peak in the low-temperature behavior of the specific heat capacity, in the vicinity of the magnetic field values, for which the highly macroscopically degenerated ground states are formed, is demonstrated and discussed. It is shown that the geometric frustration of the model together with the presence of the metamagnetic phase transitions can lead to more complicated behavior of the specific heat capacity, e.g., they have impact on the number of peaks (local maxima) in its behavior. It is also shown that the magnetocaloric effects related to the metamagnetic phase transitions are much more pronounced than those related to the frustration.