Effect of applied orthorhombic lattice distortion on the antiferromagnetic phase of CeAuSb2

We study the response of the antiferromagnetism of CeAuSb2 to orthorhombic lattice distortion applied through in-plane uniaxial pressure. The response to pressure applied along a (110) lattice direction shows a first-order transition at zero pressure, which shows that the magnetic order spontaneously lifts the (110)/(110) symmetry of the unstressed lattice. Sufficient (100) pressure appears to rotate the principal axes of the order from (110) to (100). At low (100) pressure, the transition at TN is weakly first order; however, it becomes continuous above a threshold (100) pressure. We discuss the possibility that this behavior is driven by order parameter fluctuations, with the restoration of a continuous transition being a result of reducing the point-group symmetry of the lattice.