Theoretical modeling of magnetocaloric effect in layered phase-separated metal

Magnetic cooling, based on the magnetocaloric effect (MCE), is used in industrial, household and scientific applications, as an alternative to the traditional method of cooling materials. The magnetocaloric effect is one of the most important internal thermodynamic effects of magnetic materials, in which a change in the temperature of a magnetic material can be caused by a change in the applied magnetic field. The main characteristic parameters for magnetocaloric compounds are the adiabatic temperature change (\Delta T_{ad}) and the isothermal entropy change (\Delta S_M) under an applied magnetic field [1]. Recently, non-trivial consequences of phase separation (PS) effects on the MCE in metals was derived [2]. We test the validity of MCE scenarios proposed for the model of layered metal, Hubbard model on the square lattice, exhibiting the various forms of magnetic ordering and first-order magnetic transitions between them. We employ the mean-field approximation for the ferrimagnetic (Fi), ferromagnetic (FM) and Nèel antiferromagnetic (AFM) orderings focusing an attention to the vicinity of tricitical point, where the magnetic phase transition order changes from first to second and PS bounds merges. Two the first order magnetic transitions are observed in the metal system: PM-Fi, Fi-AFM, with a further increase in temperature, a phase merger and the second order transition PM-AFM are observed, the resulting phase diagram is shown in Fig. 1. Temperature dependence of \Delta S_M in PS regions is investigated, depending on the electron filling n value, in detail in a consistent way. The study was supported by the grant of Russian Science Foundation No 18-72-10098, https://rscf.ru/en/project/18-72-10098/.

[1] Y. Xiao et al., Journal of Alloys and Compounds, 769, 916 (2018).
[2] V.V. Ivchenko, P.A. Igoshev, Physical Review B, 104, 024425 (2021).