Anisotropic magnetic entropy change in the hard ferromagnetic semiconductor VI3

Layered $\mathrm{V}{\mathrm{I}}_{3}$ has emerged as a new two-dimensional (2D) van der Waals bonded ferromagnetic semiconductor, which is an important class of materials for spintronics applications. However, the origin of ferromagnetism in $\mathrm{V}{\mathrm{I}}_{3}$ is still missing. In this work, we systematically investigate the anisotropy of magnetic properties and entropy change in a $\mathrm{V}{\mathrm{I}}_{3}$ single crystal. Based on the measurement of the angular-dependent magnetization, there is a weak sixfold in-plane symmetry and fourfold out-of-plane symmetry, indicating $\mathrm{V}{\mathrm{I}}_{3}$ possesses weak in-plane anisotropy and large out-of-plane anisotropy. Meanwhile, anisotropy of magnetic entropy change $\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$ is further studied by the isothermal magnetization, showing that the difference of $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{\mathrm{max}}$ between the $c$ axis and $ab$ plane reaches a maximum value $\ensuremath{\sim}0.95\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ with a magnetic field change of 4.5 T. With the scaling analysis of $\mathrm{\ensuremath{\Delta}}{S}_{M}$, the critical exponents can be obtained and indicate a crossover between 2D-Ising and tricritical mean-field magnetic interactions, and the rescaled $\mathrm{\ensuremath{\Delta}}{S}_{M}(T,H)$ curves fall onto a universal curve, demonstrating a second-order type of magnetic transition.