UC Berkeley

The popularization of concentrated solid-solution alloys has prompted a renewed search for atomic-scale chemical order among elements that appear randomly distributed within crystal lattices. However, confounding signals in electron diffraction experiments necessitate an immediate reliance on indirect measurements for detecting local order in compositionally complex alloys, as may be interpreted through computer simulations. For instance, both the structure and magnetization of the CrCoNi model system notably contradict ab initio theory for random alloys, but could be reconciled by the widespread presence of chemical short-range order. These simulations additionally find significant magnetic interactions in materials that are often assumed only paramagnetic, motivating further predictions of antiferromagnetism in binary Cr-Ni alloys, which are conventionally understood to have nonmagnetic ground states. This result indicates either the failure of standard theories or, as suggested by anomalous historical measurements, the existence of previously overlooked magnetic order that could persist well above ambient temperatures. In order to realistically model magnetic thermodynamics, a new Monte Carlo approach is developed and found to provide insight into the origin and prevalence of magnetic short-range order.