Single Crystal Neutron Diffuse Scattering on Nonstoichiometric Quasi-2D Ferromagnetic Fe_3-xGeTe₂

Two-dimensional (2D) van der Waals magnetic materials hold great potential for spintronics. Particularly, the recent discovery of gate-tunable room-temperature ferromagnetism in atomically thin Fe₃GeTe₂ makes it a promising candidate toward voltage-controlled low-dispassion devices. However, the magnetic properties of Fe_3-xGeTe₂ show a considerable dependence on the stoichiometry. To better understand the role of the Fe-deficiency, we have performed single crystal neutron diffuse scattering at the CORELLI spectrometer at the Spallation Neutron Source to investigate the local structure. The nonstoichiometric sample shows highly structured diffuse scattering patterns in the HK plane with a weak q dependence along the L direction. As revealed from the cross-correlation analysis with the statistical chopper, the observed diffuse scattering is mainly of a static origin. The L dependence can be partially attributed to the stacking faults. To produce the HK plane diffuse scattering features, we have performed Monte Carlo simulations to model the short-range order of the Fe vacancies and considered the lattice relaxation around the Fe vacancies.