Magnetic orderings and phase separations in a simple model of insulating systems

Konrad Jerzy Kapcia, Szymon Murawski, Waldemar Kłobus and Stanisław Robaszkiewicz

Physica A: Statistical Mechanics and its Applications, 2015, vol. 437, issue C, 218-234

Abstract: A simple effective model for a description of magnetically ordered narrow-band insulators is studied. The Hamiltonian considered consists of the effective on-site interaction (U) and intersite magnetic exchange interactions (Jz, Jxy) between nearest-neighbours. The phase diagrams and properties of this model for arbitrary chemical potential μ and arbitrary electron density n have been determined within several approaches: (i) the variational method (which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation) for any Jz,Jxy≠0 (exact in the limit of infinite dimensions), (ii) the Monte Carlo simulations on a square lattice with periodic boundary conditions for Jxy=0, and (iii) other approximate methods (inter alia: random phase approximation and spin-wave approximation) as well as (iv) rigorous treatment to obtain results concerning the ground state phase diagrams (the two last also for Jz,Jxy≠0). The investigations of the general case show that, depending on the values of interaction parameters and electron concentration n, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (Fα, α=z,xy) and nonordered (NO), but also phase separated states (PSα: Fα/NO). For a fixed n one finds the following phase transitions (both continuous and discontinuous ones) and their sequences, which can occur with increasing temperature: Fα→NO, PSα→NO, PSα→Fα→NO, PSα→Fα→PSα→NO. The system analysed exhibits also tricritical behaviour.

Keywords: Extended Hubbard model; Atomic limit; Phase separation; Magnetism; Mean-field approximation; Monte Carlo simulation (search for similar items in EconPapers)
Date: 2015
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Citations: View citations in EconPapers (1)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:phsmap:v:437:y:2015:i:c:p:218-234

DOI: 10.1016/j.physa.2015.05.074

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