Anisotropic magnetocaloric effect in single crystals of CrI3

Abstract

We report a systematic investigation of dc magnetization and ac susceptibility, as well as anisotropic magnetocaloric effect in bulk CrI3 single crystals. A second-stage magnetic transition was observed just below the Curie temperature Tc, indicating a two-step magnetic ordering. The low temperature thermal demagnetization could be well fitted by the spin-wave model rather than the single-particle model, confirming its localized magnetism. The maximum magnetic entropy change −∆S max M ∼ 5.65 J kg −1 K −1 and the corresponding adiabatic temperature change ∆T ad ∼ 2.34 K are achieved from heat capacity analysis with the magnetic field up to 9 T. Anisotropy of ∆SM (T, H) was further investigated by isothermal magnetization, showing that the difference of −∆S max M between the ab plane and the c axis reaches a maximum value ∼ 1.56 J kg −1 K −1 with the field change of 5 T. With the scaling analysis of ∆SM , the rescaled ∆SM (T, H) curves collapse onto a universal curve, indicating a second-order type of the magnetic transition. Furthermore, the −∆S max M follows the power law of H n with n = 0.64(1), and the relative cooling power RCP depends on H m with m = 1.12(1).

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

“…The calculated bands 17 , 45 with antiferromagnetic and non-magnetic ground states do not agree with the experimental results. The ferromagnetic ground state with the out-of-plane moments is also in line with the magnetic measurements 18 . Direct comparison of experimental data with the calculated bands 17 for a monolayer and bulk (FM state) CrI is shown in Fig.…”

“…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 .…”

“…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 .…”

“…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 . It is known that MCA in these systems originates due to the strong SOC induced by the iodine ligand 19 , 20 , 30 .…”

Thermal disorder driven magnetic phases in van der Waals magnet CrI3

“…A contrasting case is found in the layered transition metal halides 15 where the presence of heavy halide atoms like in CrI 3 stabilises pronounced anisotropy constants resulting in long-range magnetic order in what appears to be a single ferromagnetic transition at a relatively high temperature 6,16 . Nevertheless, recent experiments [17][18][19][20] have unveiled the presence of many subtleties in the magnetism of this compound which a single transition fails to capture. Firstly, CrI 3 exhibits both antiferromagnetic and ferromagnetic orders in thin layers driven by hydrostatic pressure 17,18 .…”