The van-der-Waals antiferromagnets TMPS3, where TM = Transition Metal, form an ideal playground for tuning both low-dimensional magnetic and electronic properties [1-4]. These are layered honeycomb antiferromagnetic Mott insulators, long studied as near-ideal 2D magnetic systems with a rich landscape of competing interactions and a variety of magnetic properties across the family.
I will give an overview of our work using high pressure as a continuous tuning parameter to control the dimensionality of these materials. Due to the weak physical inter-planar forces in such van-der-Waals materials, pressure gives us clean and selective control over the inter-planar spacing and hence interactions.
I will present magnetic, structural and electrical transport results and compare the behaviour of Fe-, V-, Mn- and NiPS3 as we tune them towards 3D structures – and Mott transitions from insulator to metal. I will focus in particular upon recent results on ultra-high-pressure neutron scattering, which have unveiled an enigmatic form of short-range magnetic order in metallic FePS3. This phase is particularly important as it most likely forms a precursor to superconductivity, and completely overturns the existing wisdom in the literature.
These neutron diffraction results made use of new cutting-edge experimental techniques  which have allowed measurements of magnetic structure through powder diffraction up to 20 GPa at the ILL - smashing the previous 10 GPa record. Piecing together our high-pressure neutron, transport and x-ray results has allowed us to map out the full phase diagram - a first in this crucial family of materials, and likely to become the archetypal example. We observe multiple transitions and new states, and an overall increase in dimensionality and associated changes in behaviour.
Dr. Christian Franz
Dr. Jitae Park