Search for pressure-induced tricriticality in Cr.

The antiferromagnetic ordering of chromium has long been known for its peculiar physical properties. One of them is the observation of the weak first-order character of the N'eel transition that is explained by the lack of a stable fixed point by Bak and Mukamel. Barak et al. predicted that by lowering the symmetry of the order parameter by the application of uniaxial pressure along the [110] direction changes the N'eel transition to second-order. In a previous experiment by Fawcett et al., irreversible broadening of the N\'eel transition was already observed between 160 bar and 300 bar, which could, however, be caused by plastic deformation. Using an improved setup with reduced stress inhomogeneities we succeeded to increase the pressure range until irreversible broadening is observed above 450 bar. Despite the observed tripling of the intensity of the magnetic Bragg peak $[0, 0, 1-\delta]$ at $p_{[110]}\geq450\,$bar, indicating a single $\bf{\text{Q}}_\pm$-domain state of the sample, no hints for a tricritical point were observed.