INVAR behaviour is the property of having zero thermal expansion over a given temperature range; something very important for certain engineering applications, and very practical in others. The physical process describing this phenomena involves a perfect balance between varying magnetic interactions in the material, and the interatomic separation as a function of temperature. Pd3Fe was recently shown to enter into such an INVAR state when the system is placed under high pressure - we aim to use this to probe the nature of the phase transition to this novel state, to better understand how INVAR materials work.