CeRu2Al2B: A new local moment 4f magnet with a complex T-H phase diagram

There is ongoing interest in the study of Ce-based compounds that are derivatives of certain structure types (e.g., ThCr$_{2}$Si$_{2}$and PbClF), as they are often associated with correlated electron phenomena. We will report results for a new system that falls into this category, CeRu$_{2}$Al$_{2}$B. This compound crystallizes in a filled variant of the layered/tetragonal CeMg$_{2}$Si$_{2}$ structure. Contrary to what is often observed for Ce-based compounds, we find pronounced local moment behavior of the Ce ions, resulting in complicated magnetic ordering at strikingly high temperatures: i.e., antiferromagnetism (AFM) at T$_{N}$ = 14.1 K followed by ferromagnetism (FM) at T$_{C}$ = 12.8 K, which is first order in character. We also find a temperature-magnetic field phase diagram that consists of three distinct ordered phases: (1) AFM, (2) spin reoriented, and (3) FM. Since this type of behavior is unusual for Ce-based compounds, we will discuss prospects for suppressing the ordered state toward T = 0 in order to produce a Doniach-like phase diagram, which may provide a route towards a FM quantum critical point.