P.C. Canfield

Magnetism and heavy fermion-like behavior in the RBiPt series

Members of the RBiPt (R=Ce–Lu with the exceptions of Pm and Eu) series have been grown as single crystals. Magnetic susceptibility and electrical resistance have been measured on all members of the series, and specific heat measurements have been performed on representatives. The high temperature resistance uniformly changes from that of a small‐gap semiconductor or semimetal seen in NdBiPt to that of a heavy‐fermion metal seen in YbBiPt, which shows a linear coefficient of specific heat at low temperatures of 8 J/K2 mole. Further, the lighter rare earth members show an unusually sharp increase in their resistance associated with antiferromagnetic ordering at low temperatures.

Magnetic and crystallographic order in α‐manganese

We have made time‐of‐flight neutron diffraction measurements on α‐manganese metal. Powder diffraction measurements were made at 14 temperatures between 15 and 305 K, and single crystal measurements were made at 15 and 300 K. We found that the crystal structure of α‐Mn is tetragonal below its Neel point of 100 K, with crystal symmetry I42m and magnetic (Shubnikov) symmetry PI421c. In agreement with the earlier results of Yamada et al., there are six independent magnetic atoms, and we found that their moments are weakly temperature dependent. The onset of magnetic order causes slight changes in the atomic positions and in the average atomic elastic constant.We have made time‐of‐flight neutron diffraction measurements on α‐manganese metal. Powder diffraction measurements were made at 14 temperatures between 15 and 305 K, and single crystal measurements were made at 15 and 300 K. We found that the crystal structure of α‐Mn is tetragonal below its Neel point of 100 K, with crystal symmetry I42m and magnetic (Shubnikov) symmetry PI421c. In agreement with the earlier results of Yamada et al., there are six independent magnetic atoms, and we found that their moments are weakly temperature dependent. The onset of magnetic order causes slight changes in the atomic positions and in the average atomic elastic constant.

NOVEL CE MAGNETISM IN CEDIPNICTIDE AND DI-CE PNICTIDE STRUCTURES

Results of electrical resistance and magnetic susceptibility measurements on Ce2Bi, Ce2Sb, CeScGe, CeScSi and CeSb2 are presented. Ce2Bi and Ce2Sb have antiferromagnetic transitions at low temperatures, while CeSb2, CeScGe and CeScSi have ferromagnetic transitions, CeScGe having a Tc = 46 K. The data are analyzed with respect to the similarities of the two crystal structure groups that these materials fall into: CeSb2 having the LaSb2 structure and the other materials all having the La2Sb structure.

Evidence for a 'coherence' gap in Ce3Bi4Pt3

Abstract We present the results of electronic transport, magnetic susceptibility, and thermodynamic measurements on single crystals of the cubic compound Ce3Bi4Pt3. The susceptibility displays a broak peak centered at Tmax = 80K, which in Ce compounds is usually indicative of mixed valence and moderately heavy-electron behavior. Both the electronic transport properties and the low-temperature specific heat indicate that Ce3Bi4Pt4 is nonmetallic with a transport energy gap of roughly 35 K. We argue that this temperature is close to that scale over which coherence should develop in a periodic metallic system with Tmax = 80K. Resistivities typical of a Kondo-impurity system are realized when the compound is alloyed with moderate amounts of lanthanum. Further, lanthanum substitution increases the low-temperature specific heat to a value consistent with the single-ion energy scale determined from the magnetic susceptibility.

Antiferromagnetism and enhanced specific heat in CeM2Sn2 (M = Ni, Ir, Cu, Rh, Pd and Pt)

Abstract Specific heat, DC susceptibility, and resistivity measurements on annealed, polycrystalline samples of CeM2Sn2, where M = Ni, Ir, Cu, Rh, Pd, or Pt, indicate that each of these compounds orders antiferromagnetically with transition temperatures ranging from TN = 4.1 to ≈ 0.5 K. All these materials have significant enhancements of the specific heat just before the transition, which can be as large as ∼ 3.5J/mol K2 in some cases. Provided the enhanced heat capacities above TN are associated with large effective masses, the anomalously low ordering temperature and the very large C/T suggest that TN and the Kondo temperature TK are comparable, making these materials particularly attractive for studying the interplay between these competing interactions. The susceptibility for each member of the series except M = Ir follows a Curie-Weiss behavior with a high-temperature effective moment μ eff ∼ 2.5μ B Ce and a small negative paramagnetic Curie temperature.

Electron-hole doping of the metal-insulator transition compound RENiO3

Abstract We have studied the effects of electron and hole doping on the electronic properties of Nd(Pr)NiO3, charge-transfer compounds undergoing a metal-insulator transition. Electron-hole asymmetry associated with the suppression of the metal-insulator transition was observed. In addition, the Hall coefficient was found to vanish at the transition temperature.

Ce3Bi4Pt3 and hybridization Gap physics

Abstract Basic thermodynamic and transport properties of Ce 3 Bi 4 Pt 3 are reviewed. Although the susceptibility displays a canonical mixed valence temperature dependence, the electrical resistance, thermoelectric power and specific heat are those associated with a small gap semiconductor in which the gap is due to hybridization of the renormalized f and conduction electrons. In addition to this, a surprising correlation between the magnetic susceptibility and the thermal expansion as well as a simple theoretical framework within which hybridization-gapped systems can be viewed are presented.

Thermal history-dependent superconductivity and local structure in La2CuO4+δ

Abstract DC magnetic susceptibility measurements reveal a dependence of the superconducting critical temperature ( T c ) on the cooling rate ( R ) in super-oxygenated La 2 CuO 4+δ . Bulk T c s vary by ≈ 4 K depending on whether the sample is “quenched” or slow cooled through a narrow temperature range around 195 ± 10 K. 139 La nuclear quadrupole resonance spectroscopy (NQR) shows the appearance of a feature indicating a distribution of local structures in the metallic phase below ≈ 195 K, the same temperature regime where R is critical for T c . The spectral weight associated with the metallic phase appears to increase for rapid cooling.

Effects of doping on hybridization gapped materials

Doping studies are presented on three materials exhibiting hybridization gaps: Ce{sub 3}Bi{sub 4}Pt{sub 3}, U{sub 3}Sb{sub 4}Pt{sub 3}, and CeRhSb. In the case of trivalent La, Y, or Lu substituting for Ce or U, there is a suppression of the low temperature gap and an increase in the electronic specific heat, {gamma}. In the case of tetravalent Th substitutions for U there is no change in {gamma} and in the case of tetravalent Zr substitution for Ce in CeRhSb, there is an enhanced semiconductor-like behavior in the electrical resistance. These results are discussed in the light of a simple model of hybridization gapped systems. 12 refs., 3 figs.

Electronic transport in Ce3Bi4Pt3: evidence for a temperature-dependent hybridization gap

Abstract We present an analysis of transport data from Ce 3 Bi 4 Pt 3 to deteermine the energy gap temperature dependence E g ( T ). E g ( T ) is a decreasing function of temperature. This result is consistent with the gap being a product of many-body correlations in which E g ( T ) is scaled by the Kondo energy scale T K .