Anisotropic magnetic, magnetocaloric properties, and critical behavior studies of CVT-grown single-crystalline Fe3−xGeTe2

A comprehensive study of magnetic, room-temperature M\"ossbauer spectroscopic, room-temperature Raman spectroscopic, magnetocaloric, and critical behavior properties of chemical vapor transport (CVT) grown single-crystalline ${\mathrm{Fe}}_{3\ensuremath{-}x}{\mathrm{GeTe}}_{2}$ ($x\ensuremath{\approx}0.3$) (F3GT) have been performed. The single crystal of F3GT has been formed in a van der Waals force bonded layered compound. The compound crystallizes in hexagonal crystal structure with space group $\mathit{P}{6}_{3}/\mathit{mmc}$. Temperature variation of dc and ac magnetic susceptibility of F3GT reveals a paramagnetic to ferromagnetic transition at $\ensuremath{\approx}180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ (${T}_{\mathrm{C}}$). Field variation of magnetic isotherm in the magnetically ordered state at 5 K reveals strong anisotropy with crystallographic $c$ axis as the easy axis of magnetization. A weak itinerant behavior of Fe spins is also ascertained from the magnetization studies. Magnetocaloric effect in terms of isothermal magnetic entropy change has been estimated to be $\ensuremath{\approx}\ensuremath{-}2.6$ J/kg-K near ${T}_{\mathrm{C}}$ for a field change of 100 kOe along crystallographic $c$ direction. The magnetic transition at ${T}_{\mathrm{C}}$ is found to be of second order. Critical behavior analysis performed for the easy magnetization axis direction in CVT-grown F3GT by modified Arrott plots and Kouvel-Fisher technique suggests that this system does not belong to a particular universality class. However, the critical exponents assume values $\ensuremath{\beta}=0.321, \ensuremath{\gamma}=1.179$, and $\ensuremath{\delta}=4.67$. Isothermal magnetization curves at different temperatures in the closed vicinity of ferromagnetic transition of F3GT obey the scaling hypothesis using the estimated critical exponents wherein the magnetization vs field data below and above magnetic transition collapse onto two branches of the universal curves. The critical behavior analyses confirm the weak itinerant ferromagnetic long-range-type interaction due to itinerant $3d$ electrons and the interaction is very close to the three-dimensional Heisenberg type, wherein the occurrence of long-range-type interaction between the magnetic spins decays as $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.74}$ in F3GT.