Critical behavior of the van derWaals bonded ferromagnet Fe3-xGeTe2

The critical properties of the single-crystalline van der Waals bonded ferromagnet Fe3-xGeTe2 were investigated by bulk dc magnetization around the paramagnetic to ferromagnetic (FM) phase transition. The Fe3-xGeTe2 single crystals grown by self-flux method with Fe deficiency x approximate to 0.36 exhibit bulk FM ordering below T-c = 152 K. The Mossbauer spectroscopy was used to provide information on defects and local atomic environment in such crystals. Critical exponents beta = 0.372(4) with a critical temperature T-c = 151.25(5) K and gamma = 1.265(15) with T-c = 151.17(12) K are obtained by the Kouvel-Fisher method, whereas d = 4.50(1) is obtained by a critical isotherm analysis at T-c = 151 K. These critical exponents obey theWidom scaling relation delta = 1 + gamma/beta, indicating self-consistency of the obtained values. With these critical exponents the isothermM(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) approximate to r(-(3+ sigma)) with sigma = 1.89.