Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetism

The van der Waals ferromagnet Fe5GeTe2 has a Curie temperature T-C of about 270 K, which is tunable through controlling the Fe deficiency content and can even reach above room temperature. To achieve insights into its ferromagnetic exchange that gives the high T-C, the critical behavior has been investigated by measuring the magnetization in Fe5GeTe2 crystal around the ferromagnetic ordering temperature. The analysis of the measured magnetization by using various techniques harmonically reached to a set of reliable critical exponents with T-C=273.7 K, beta = 0.3457 +/- 0.001, gamma = 1.40617 +/- 0.003, and delta = 5.021 +/- 0.001. By comparing these critical exponents with those predicted by various models, it seems that the magnetic properties of Fe5GeTe2 could be interpreted by a three-dimensional magnetic exchange with the exchange distance decaying as J(r) approximate to r(-4.916), close to that of a three-dimensional Heisenberg model with long-range magnetic coupling.