Critical behavior and magnetocaloric effect in VI3

Abstract

Layered van der Waals ferromagnets are promising candidates for designing new spintronic devices. Here we investigated the critical properties and magnetocaloric effect connected with ferromagnetic transition in layered van der Waals VI3 single crystals. The critical exponents β = 0.244(5) with a critical temperature Tc = 50.10(2) K and γ = 1.028(12) with Tc = 49.97(5) K are obtained from the modified Arrott plot, whereas δ = 5.24(2) is obtained from a critical isotherm analysis at Tc = 50 K. The magnetic entropy change −∆SM (T, H) features a maximum at Tc, i.e., −∆S max M ∼ 2.64 (2.27) J kg −1 K −1 with out-of-plane (in-plane) field change of 5 T. This is consistent with −∆S max M ∼ 2.80 J kg −1 K −1 deduced from heat capacity and the corresponding adiabatic temperature change ∆T ad ∼ 0.96 K with out-of-plane field change of 5 T. The critical analysis suggests that the ferromagnetic phase transition in VI3 is situated close to a three-to two-dimensional critical point. The rescaled ∆SM (T, H) curves collapse onto a universal curve, confirming a second-order type of the magnetic transition and reliability of the obtained critical exponents.

Valence band electronic structure of the van der Waals ferromagnetic insulators: VI$$_3$$ and CrI$$_3$$

“…Bulk CrI and VI single crystals were grown by the chemical vapor transport method (CVT). The details of sample growth and characterization can be found elsewhere 21 , 27 . The as-grown samples were clamped to the sample holder under argon atmosphere, cleaved with kapton tape inside UHV, and studied by ARPES.…”

“…In case of CrI , the Cr has half filled t level yielding S = 3/2 20 , while VI , V has two valence electrons in the t states, yielding S = 1 25 . Bulk CrI and VI are layered insulating 2D ferromagnets with = 61 K and 50 K 18 , 27 and band gap of 1.24 eV and 0.6–0.67 eV, respectively 25 , 38 . Upon cooling, CrI undergoes a phase transition 220 K from the high-temperature monoclinic (C2/m) to the low-temperature rhombohedral (R ) phase 39 .…”

“…Upon cooling, CrI undergoes a phase transition 220 K from the high-temperature monoclinic (C2/m) to the low-temperature rhombohedral (R ) phase 39 . VI also undergoes a structural phase transition at 80 K. Above transition temperature it has a trigonal structure (space group R ) 26 , 27 but exact symmetry of the low-temperature structure is not established yet 23 , 25 , 40 . The experimental studies on these systems are mainly focused on the magnetic and structural properties 8 , 18 , 22 , 23 , 25 – 27 , 41 .…”

“…VI also undergoes a structural phase transition at 80 K. Above transition temperature it has a trigonal structure (space group R ) 26 , 27 but exact symmetry of the low-temperature structure is not established yet 23 , 25 , 40 . The experimental studies on these systems are mainly focused on the magnetic and structural properties 8 , 18 , 22 , 23 , 25 – 27 , 41 . Magnetic measurements show the presence of magnetocrystalline anisotropy (MCA) in these systems, favoring an out-of-plane orientation of magnetic moments 18 , 22 , 25 , 32 .…”

“…For www.nature.com/scientificreports/ the electron energy of 228 eV, only one set of spots are seen ( Fig. 2e), suggesting the trigonal symmetry of the crystal (space group R 3 ) 26,27 .…”