Critical behavior of the van der Waals bonded ferromagnet Fe3−xGeTe2

Abstract

The critical properties of the single-crystalline van der Waals bonded ferromagnet Fe3−xGeTe2 were investigated by bulk dc magnetization around the paramagnetic (PM) to ferromagnetic (FM) phase transition. The Fe3−xGeTe2 single crystals grown by self-flux method with Fe deficiency x ≈ 0.36 exhibit bulk FM ordering below Tc = 152 K. The Mössbauer spectroscopy was used to provide information on defects and local atomic environment in such crystals. Critical exponents β = 0.372(4) with a critical temperature Tc = 151.25(5) K and γ = 1.265(15) with Tc = 151.17(12) K are obtained by the Kouvel-Fisher method whereas δ = 4.50(1) is obtained by a critical isotherm analysis at Tc = 151 K. These critical exponents obey the Widom scaling relation δ = 1 + γ/β, indicating self-consistency of the obtained values. With these critical exponents the isotherm M (H) curves below and above the critical temperatures collapse into two independent universal branches, obeying the single scaling equation m = f±(h), where m and h are renormalized magnetization and field, respectively. The exponents determined in this study are close to those calculated from the results of the renormalization group approach for a heuristic model of three-dimensional Heisenberg (d = 3, n = 3) spins coupled with the attractive long-range interactions between spins that decay as J(r) ≈ r −(3+σ) with σ = 1.89.

Critical behavior of intercalated quasi-van der Waals ferromagnet Fe0.26TaS2

“…As expected, Cr 2 Si 2 Te 6 and Cr 2 Ge 2 Te 6 have β values inside this window and they both demonstrate 2D Ising type coupling [10,11]. While CrI 3 , Fe 3 GeTe 2 , and Mn 3 Si 2 Te 6 are all found to exhibit the 3D critical phenomenon with β > 0.25 [8,9,[46][47][48]. It is interesting that 3D magnetic characteristics are observed in vdW-bonded magnets, and it could be explained by the fact that CrI 3 and Fe 3 GeTe 2 have smaller vdW gaps than Cr 2 Si 2 Te 6 and Cr 2 Ge 2 Te 6 [46,49], which gives rise to much stronger interlayer coupling.…”

“…Unlike the conventional bulk ferromagnets in which 3D Heisenberg coupling dominates [7], the critical behavior in these vdW crystals may vary from one material to another. For example, bulk CrI 3 and Fe 3 GeTe 2 are consistent with 3D Heisenberg type behavior [8,9], but the Ising model is prevailing in Cr 2 Si 2 Te 6 and Cr 2 Ge 2 Te 6 [10,11] due to their different strengths of interlayer coupling. Moreover, even for the same material, the variation of thickness may lead to changes in magnetic properties.…”

Controlling the Magnetic Anisotropy of the van der Waals Ferromagnet Fe3GeTe2 through Hole Doping

“…xGeTe2. 22 Also, from earlier reports on the hard-axis (in-plane) hysteresis loops of bulk Fe3GeTe2 and Fe3-xGeTe2, [23][24][25] we estimate roughly 7 fold decrease in the magnetic anisotropy due to the Fe deficiency. In our study, we find that the decrease in magnetic anisotropy holds true down to the ultrathin regime.…”

“…This strongly suggests that the drastic reduction of MAE is not likely from the decreased spin moments but from the change in SOC. Since the valence of Fe ions in Fe3-xGeTe2 is expected to be in between Fe 3+ and Fe 2+ , 24,25 the 1 h/f.u. doping corresponds to a Fe deficiency of x = 0.33 -0.5, close to x ~ 0.36 of the Fe3-xGeTe2 measured in this study; the ten-fold decrease in MAE is consistent with the large reduction of coercivity and magnetic anisotropy observed by…”

“…The electronic structures of Fe3-xGeTe2 measured by ARPES shows significant chemical potential shifts with enlarged hole and reduced electron pockets, supporting the mechanism of electronic structure driven change in the magnetic anisotropy.Experimental SectionSingle crystal growth. Single crystals of Fe3-xGeTe2 were grown from molten metallic fluxes as described previously 24. Magnetic characterization of Fe3-xGeTe2.…”