Possible Tricritical Behavior and Anomalous Lattice Softening in van der Waals Itinerant Ferromagnet Fe3GeTe2 under High PressureSupported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0305704 and 2016YFA0401804), the National Natural Science Foundation of China (Grant Nos. 11774352, U1832214, U19A2093, 11804344, U1632275, 11874362, 11704387, and U1932152), the Users with Excellence Project of Hefei Center CAS (Grant

Abstract

We present a high-pressure study of van der Waals ferromagnetic metal Fe3GeTe2 through electrical transport and Raman scattering measurements in diamond anvil cells at pressures up to 22.4GPa. Upon compression, the ferromagnetic transition temperature Tc manifested by a kink in resistance curve decreases monotonically and becomes undiscernable around Pc = 10GPa, indicative of suppression of the itinerant ferromagnetism. Meanwhile, by fitting the low temperature resistance to the Fermi liquid behavior of R = R0 + AT2, we found that R0 shows a cusp-like anomaly and the coefficient A diverges around Pc. These transport anomalies imply a tricritical point as commonly observed in itinerant ferromagnets under pressure. Unexpectedly, the Raman-active E2g and A1g modes soften remarkably after an initial weak hardening and the peak widths of both modes broaden evidently on approaching Pc, followed by complete disappearance of both modes above this critical pressure. A possible underlying mechanism for such anomalous lattice softening near Pc is discussed.