Critical behavior and anisotropic magnetocaloric effect in off-stoichiometric van der Waals ferromagnet Fe3-xGaTe2

Abstract

The evolution of magnetic interactions, critical properties and magnetocaloric effects of off-stoichiometric room-temperature van der Waals Fe_3-xGaTe₂ are systematically investigated. Density functional theory (DFT) calculations reveal that the ferromagnetic exchange interactions between different Fe atoms play an important role in magnetic couplings and the change of Curie temperature T_C. Moreover, the Fe vacancy in different sites can also significantly affect the T_C. For Fe_2.72GaTe_2.01 single crystal, the critical exponents β of 0.474(3) and γ of 1.018(9) with T_C at 336.7 K are obtained by the modified Arrott plot, whereas the critical exponent δ of 2.72(1) is yielded from a critical isotherm analysis at T_C. The results of these critical exponents indicate that off-stoichiometric Fe_2.72GaTe_2.01 shows an approximate mean-field critical behavior. Furthermore, the exchange interaction distance decays as J ≈ r^-4.53 proving the long-range ferromagnetism. In addition, the single crystal exhibits an anisotropic magnetocaloric behavior. The maximal value of the magnetic entropy change ΔS_m reaches -1.7 (-1.0) J kg^-1K⁻¹ for a magnetic field change of 50 kOe in H//c axis (H//ab plane). Based on the field dependent ΔS_m, the calculated critical exponent n is less than 2 at around T_C, confirming a second-order type of the magnetic transition and reliability of the obtained critical exponents.