Competing antiferromagnetism in a quasi-2D itinerant ferromagnet: Fe₃GeTe₂

Fe₃GeTe₂ is known as an air-stable layered metal with itinerant ferromagnetism with a transition temperature of about 220 K. From our extensive dc and ac magnetic measurements, we have determined that the ferromagnetic layers of Fe₃GeTe₂ actually order antiferromagnetically along the c-axis below 152 K. The antiferromagnetic state was further substantiated by theoretical calculation to be the ground state. A magnetic structure model was proposed to describe the antiferromagnetic ground state as well as competition between antiferromagnetic and ferromagnetic states. Fe₃GeTe₂ shares many common features with pnictide superconductors and may be a promising system in which to search for unconventional superconductivity.