Magnetic and magneto-transport studies in van der Waals Fe5−xGeTe2 flakes

The layered van der Waals metallic material Fe5−xGeTe2, which has near room-temperature itinerant ferromagnetism, offers unprecedented opportunities to explore exotic phenomena and functionalities as well as prospective uses in spintronic or quantum devices. However, the intriguing magnetic ground state of Fe5−xGeTe2 is quite complicated and remains controversial. In this work, we investigate the magnetic ordering transitions in Fe5−xGeTe2 nanoflakes through magneto-transport measurements. The anomalous Hall resistance increases with rising temperature, reaching its maximum at 100 K. Meanwhile, a clear butterfly-shaped magnetoresistance hysteresis was observed with opposite dependence on the switching field around this critical temperature. All experimental results point to the scenario that Fe5−xGeTe2 transitions from the paramagnetic to ferromagnetic state at 265 K and then evolves to a ferrimagnetic state at 100 K. Our work promotes the understanding of magnetism in Fe5−xGeTe2 and motivates further efforts to develop room-temperature spintronic devices based on Fe5−xGeTe2.