Thermodynamics of a model solid with magnetoelastic coupling

Abstract

In the paper a study of a model magnetoelastic solid system is presented. The system of interest is a mean-field magnet with nearest-neighbour ferromagnetic interactions and the underlying s.c. crystalline lattice with the long-range Morse interatomic potential and the anharmonic Debye model for the lattice vibrations. The influence of the external magnetic field on the thermodynamics is investigated, with special emphasis put on the consequences of the magnetoelastic coupling, introduced by the power-law distance dependence of the magnetic exchange integral. Within the fully self-consistent, Gibbs energy-based formalism such thermodynamic quantities as the entropy, the specific heat as well as the lattice and magnetic response functions are calculated and discussed. To complete the picture, the magnetocaloric effect is characterized by analysis of the isothermal entropy change and the adiabatic temperature change in the presence of the external pressure.

Hubbard pair cluster with elastic interactions. Studies of thermal expansion, magnetostriction and electrostriction

“…In the paper the total grand potential has been constructed for the dimer system, in which the magnetic, elastic and thermal vibration energies play important roles. The similar attempts at the total Gibbs energy construction, i.e., consisting in summation of various energy contributions, have been undertaken, so far, for the bulk materials [61,[63][64][65][66]. According to our knowledge, for the Hubbard dimer such method has not been presented previously.…”

Thermodynamic model of a solid with RKKY interaction and magnetoelastic coupling

“…In particular, by reduction of the long-range RKKY interaction and by leaving only NN magnetic interaction, as well as without energy of electronic subsystem the formalism will be equivalent to that developed in our previous papers (Refs. [40,41]). Such a method could be applicable to magnetic insulators.…”

“…In our previous papers [40,41], the thermodynamic model for the magnetoelastic couplings was presented, for the simplest case when the magnetic interaction between localized spins was of Heisenberg type. The energy of itinerant electrons was not considered in that approach, thus restricting the model to magnetic insulators.…”

Anomalous spin frustration enforced by a magnetoelastic coupling in the mixed-spin Ising model on decorated planar lattices

“…A substantial progress in this research area has been recently made by Balcerzak and co-workers when developing a phenomenological theory based on a self-consistent variational approach, which combines different approximations for individual subsystems as for instance a meanfield approximation for a magnetic subsystem, Debey approximation for a lattice subsystem, etc. [1][2][3] It is notorious that the leading-order interaction term between localized spins of insulating magnetic solids is an indirect superexchange coupling, which according to the Kramers-Anderson mechanism basically depends on an overlap of atomic wave functions [4,5]. The superex-change coupling (further referred to as the exchange coupling) thus strongly depends on an instantaneous distance between the magnetic atoms, which are subject to a perpetual temperature-dependent lattice vibrations.…”