Emergent magnetic phases in pressure tuned van-der-Waals antiferromagnet FePS3

Abstract

Layered van-der-Waals 2D magnetic materials are of great interest in fundamental condensed matter physics research, as well as for potential applications in spintronics and device physics. We present neutron powder diffraction data using new ultra-high-pressure techniques to measure the magnetic structure of Mott-insulating 2D honeycomb antiferromagnet FePS3 at pressures up to 183 kbar and temperatures down to 80 K. These data are complemented by high-pressure magnetometry and reverse Monte Carlo modelling of the spin con figurations. As pressure is applied, the previously-measured ambient-pressure magnetic order switches from an antiferromagnetic to a ferromagnetic interplanar interaction, and from 2D-like to 3D-like character. The overall antiferromagnetic structure within the ab planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from k = (0, 1, 1/2 ) to k = (0, 1, 0), a halving of the magnetic unit cell size. At higher pressures, coincident with the second structural transition and the insulator-metal transition in this compound, we observe a suppression of this long-range-order and emergence of a form of magnetic short-range order which survives above room temperature. Reverse Monte Carlo fi tting suggests this phase to be a short-ranged version of the original ambient pressure structure - with the Fe moment size remaining of similar magnitude and with a return to antiferromagnetic interplanar correlations. The persistence of magnetism well into the HP-II metallic state is an observation in contradiction with previous x-ray spectroscopy results which suggest a spin-crossover transition.