V. Goruganti

Magnetic and thermodynamic properties of Nd2Ni2Pb

We report magnetic and thermodynamic measurements for Nd2Ni2Pb, one of the recently discovered R2Ni2Pb family of layered intermetallics. A specific heat jump at 19 K corresponds to an antiferromagnetic transition involving crystal-field-split Nd levels. Magnetization measurements show this phase to have a canted structure, with a metamagnetic transition to an aligned phase occurring in H=3T at low temperatures. The single antiferromagnetic phase stands in contrast to the more complex magnetic structures and multiple transitions in the heavy-rare-earth members of this family.

Electrical transport, heat capacity, and high-field magnetization study in intermetallic Ni2CeSn compound

Magnetization, heat capacity, and electrical resistivity measurements were performed on a Ni2CeSn compound (orthorhombic structure) in the temperature range of 2–300K. This compound is paramagnetic down to 6K. At higher temperatures above T=150K, the magnetic susceptibility obeys Curie–Weiss behavior yielding an effective magnetic moment μeff=2.56μB∕f.u., which is very close to that of the free Ce3+ ion (2.54μB) with a high negative Curie–Weiss temperature, ΘCW=−170K. As the temperature is decreased, the magnetic moment decreases gradually to 0.43μB∕f.u. at 4.2K. We also infer that, based on the high field (up to 23T) magnetization and the magnetic susceptibility data, a crystal-field splitting of cerium atoms becomes significant at temperatures below 150K. We used heat capacity and resistivity measurements to determine the crystal-field splitting of the Ce3+ magnetic sublevels. It is found that the ground magnetic state for the Ce3+ is a doublet of Jz=±1∕2 states, with a first excited quartet of Jz=±3∕2 ...

Magnetic phase transitions in R5NiPb3 (R=Ce, Nd, and Gd)

We report magnetic and thermodynamic measurements for R5NiPb3 (R=Ce, Nd, Gd). Gd5NiPb3 has a transition at 68K, apparently ferrimagnetic from specific heat and magnetization measurements. For Ce5NiPb3, a phase transition is observed in heat capacity at 48 K, with the field dependence of heat capacity and magnetization also indicating ferrimagnetic behavior. Ce5NiPb3 shows metamagnetism at low temperatures, behavior rather similar to Nd5NiPb3 with its previously reported magnetic ordering below 42 K. Using nonmagnetic La5NiPb3, we isolated the magnetic heat capacity for all three materials. The results include a relatively large linear-T term in the specific heat and integrated magnetic entropies consistently smaller than expected.

Phase transitions in NdNiPb and Nd5NiPb3

We report magnetic and thermodynamic measurements for NdNiPb and Nd5NiPb3. High-temperature Curie-Weiss fits yield effective moments per Nd of 3.59μB for NdNiPb and 3.70μB for Nd5NiPb3. These are close to the Nd3+ ionic moment, 3.62μB, showing that Ni is nonmagnetic in both cases. For NdNiPb a peak seen in both the magnetization and specific heat at 3.5K indicates an antiferromagnetic transition at that temperature. Specific heat measurements show this transition to be formed from crystal-field-split Nd magnetic levels, and a fit yields values for crystal field splitting. Nd5NiPb3 exhibits two magnetic transitions, an antiferromagnetic transition at 42K, and an apparently weak-ferromagnetic canting transition at 8K. These are confirmed by specific heat measurements. M-H curves show metamagnetism at temperatures between the two magnetic transitions.

Transition‐Metal Substitution in Semiconducting Ba8Ga16Ge30 Clathrates

We report magnetization, transport, and 71Ga NMR properties of Ni‐ and Fe‐substituted type‐I Ba6Ge30Ga16 clathrates. While Fe substitutes partially into the lattice, Ni substitutes readily for Ga, and we prepared samples with composition up to Ba8Ge30Ga10Ni6. Results indicate low‐density metallic behavior for all samples, with little change in electronic structure caused by Fe or Ni substitution. NMR relaxation behavior (T1) and Knight shifts in all samples exhibited a constant Korringa product (K2T1T) characteristic of metallic behavior with small exchange enhancement.