An anomalous magnetic phase transition at 10 K in Nd7Rh3

The compound Nd7Rh3, crystallizing in a Th7Fe3-type hexagonal structure, has been shown recently by us to exhibit a signature of a 'magnetic phase-coexistence phenomenon' below 10 K after field cycling. This is uncharacteristic of stoichiometric intermetallic compounds, and bears a relevance to the trends in the field of 'electronic phase-separation'. In order to characterize this compound further, we have carried out dc magnetic susceptibility (χ), electrical resistivity, magnetoresistance and heat-capacity measurements as a function temperature (T = 1.8-300 K). The results reveal that this compound exhibits another unusual finding at the 10 K transition in the sense that the plot of χ(T) shows a sharp increase in the 'field-cooled' cycle, whereas the 'zero-field-cooled' curve shows a downturn below the transition. In addition, the sign of magnetoresistance is negative and the magnitude is large over a wide temperature range in the vicinity of the magnetic ordering temperature, with a sharp variation at 10 K. The results indicate that the transition below 10 K is first-order in its character. (letter to the editor)