Uniaxial pressure dependencies of the phase boundary of TlCuCl3

We present a thermal expansion and magnetostriction study of TlCuCl 3 , which shows a magnetic-field-induced transition from a spin gap phase to a Neel-ordered phase. Using Ehrenfest relations we derive huge and strongly anisotropic uniaxial pressure dependencies of the respective phase boundary, e.g., the transition field changes by about ±185%/GPa depending on the direction of uniaxial pressure.