The influence of interplanar coupling on the entropy and specific heat of the bilayer ferromagnet

Abstract

The Pair Approximation method is applied to studies of the magnetic Ising-Heisenberg bilayer with simple cubic structure and spin S = 1/2. The method allows to take into account quantum effects related to Heisenberg couplings. In the paper the entropy and magnetic contribution to the specific heat are calculated. A special attention is paid to the case when the planes are magnetically non-equivalent and the interplanar coupling is relatively weak. A double peak structure in the temperature dependence of the specific heat and the entropy change in the external field is found. When the system is strongly anisotropic (the case of Ising couplings) the Exact Calculations for Finite Cluster are performed for comparison with the Pair Approximation method.

The thermodynamic properties of a spin-1/2 Heisenberg ferromagnetic system using Oguchi's method

“…The model includes the cluster with two spins which are a pair of nearest neighbor atoms selected, and assumes that the pair of spins is coupled to the rest of the crystal by an effective field proportional to the magnetization. Many kinds of Hamiltonians can be investigated by using this method [14][15][16][17][18][19][20][21][22][23][24]. But, very few of them deal with the thermodynamic properties [23,24].…”

Ising versus Potts criticality in low-temperature magnetothermodynamics of a frustrated spin- 12 Heisenberg triangular bilayer

“…In this part we will adapt the graph-theoretical approach developed in Ref. 53 in order to find an exact solution of the effective 3×3 triangular Ising model given by the Hamiltonian (16) with the specific value of linear size L = 3 (see Fig. 13 for a schematic illustration).…”

“…All basic magnetothermodynamic quantities of the effective Ising model on a triangular lattice given by Eqs. (16) and (17) such as magnetization, susceptibility and specific heat can be obtained by exact calculations for small finite-size systems (see Appendix B) or by performing classical Monte Carlo (MC) simulations implementing standard Metropolis sampling for larger system sizes. In addition, a few exact results are known for the Ising model on a triangular lattice on assumption that the effective field or temperature becomes zero.…”

“…Let us conclude our survey of the most interesting results by constructing global phase diagrams of the frustrated spin- 1 2 Heisenberg triangular bilayer in the field-temperature plane as obtained from a mapping correspondence (16), (17) with the effective Ising model on a triangular lattice. The phase diagram of the spin-1 2 Heisenberg FM/AF triangular bilayer can be descended from exact results for the effective triangular Ising ferromagnet, 42 while the phase diagram of the spin- Heisenberg FM/AF triangular bilayer with the ferromagnetic interdimer interaction J 1 < 0 depicted in Fig.…”

The dynamic magnetic behaviors of the Blume–Capel Ising bilayer system

“…Research on magnetic bilayers has received much interest both from the experimental and theoretical point of view in recent years [1][2][3][4][5][6][7][8][9][10]. Experimentally, several works have been published on the properties of the magnetic bilayer such as FePt/Fe [11], FM/TbFe (FM=Fe, Py-permalloy, FeCo) [12], SiGe, SiC and GeC [13], Ni/Au [14], Fe/Ni and Fe/Co [15].…”