Pressure effect on the crystal lattice of unconventional superconductor UCoGe

High-pressure techniques were used to determine the structural behaviour of the superconducting ferromagnet UCoGe up to 30 GPa enabling us to determine the link between the effect of pressure on the material magnetic properties and crystal structure. The TiNiSi type structure of UCoGe was preserved up to the highest pressure. The a direction, equivalent to the shortest U-U links, was identified as the critical soft direction. The data are compared with the structural variations in UCoGe α-hydride, which becomes non-magnetic and non-superconducting despite a volume expansion. We show that at least in this case, but probably more generally, the structure impact of hydrogenation is definitely not equivalent to negative pressure.