Hidden order to antiferromagnetic transition in URu$_2$Si$_2$

The second-order phase transition in the heavy fermion compound URu$_2$Si$_2$ continues to confound efforts to reveal its true nature, and bears the moniker "hidden order" with good reason. While the order parameter remains mysterious, antiferromagnetism is easily induced with modest chemical substitution. The proximity of these two phases offers tantalizing clues about the nature of the hidden order phase. We present data on the antiferromagnetic phase, revealing the similarities and the differences between the two phases, including evidence for effects above the transition temperature. The implications of these findings for the hidden order parameter will be discussed.