Magnetism of Nd³⁺ ions in Nd₅Rh₄Sn₁₀

In the family of rare-earth transition metal silicides, compounds belonging to the series R₅Ir₄Si₁₀ (where R is a rare-earth element from Dy to Lu and Y) exhibits multiple phase transitions. However, there exists a series R₅Rh₄Sn₁₀, which can only be formed with light rare-earth elements from Ce to Nd. In this work, we report detailed resistivity, susceptibility, magnetization, heat-capacity, thermal expansion, and magnetoresistance studies, which suggest that the Nd³⁺ moments undergo unusual magnetic orderings in a single crystal of Nd₅Rh₄Sn₁₀. A second-order magnetic transition at 7.15 K is followed by a first-order transition below 6.15 K that results in a huge heat-capacity peak of 100 J/mol K. The two transitions are strongly suppressed by a magnetic field (4 T) along the c axis while they are only weakly influenced by fields as high as 16 T in the basal plane. Moreover, the magnetoresistance data along the a and c axes from 1.5 to 15 K in fields up to 18 T revealed a giant positive magnetoresistance along the a axis below 6 K and clear evidence of a metamagnetic transition along the c axis. We attribute this unusual magnetic behavior to the unique crystal structure of this Nd₅Rh₄Sn₁₀ compound with its three different Nd sites.