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MA: Fachverband Magnetismus

MA 5: Spin Structures and Magnetic Phase Transitions I

MA 5.4: Vortrag

Montag, 18. März 2024, 10:15–10:30, EB 202

Thermal phase transitions of a spin-1/2 Ising-Heisenberg model on the extended Lieb lattice in a magnetic field — •Jozef Strecka and David Sivy — Faculty of Science, P. J. Safarik University, Kosice, Slovakia

The spin-1/2 Ising-Heisenberg model on the extended Lieb lattice can be rigorously mapped in presence of the external magnetic field to an effective spin-1/2 Ising square lattice with temperature-dependent interaction and field. It is shown that an effective field may vanish along a phase boundary between a quantum monomer-dimer phase and a classical ferrimagnetic phase, which allows an exact determination of thermal phase transitions between these two phases even in presence of non-zero magnetic field. Similar thermal phase transitions can be additionally found between a quantum antiferromagnetic phase and a disordered paramagnetic phase of the model. It is demonstrated that the line of discontinuous phase transitions terminates at the Ising critical point corresponding to a continuous phase transition. The aforementioned exact results for discontinuous and continuous thermal phase transitions in a magnetic field are corroborated by classical Monte Carlo simulations.

This work is supported by Slovak Research and Development Agency under the contract No. APVV-20-0150.

Keywords: Ising-Heisenberg model; thermal phase transitions; Ising critical points; exact results; Monte Carlo simulations