Russell E. Walstedt

Relaxation anomalies of 69/71Ga NQR in the paramagnetic state of the itinerant antiferromagnet UGa3: Possible evidence for a crossover to localized spin fluctuations and development of orbital fluctuations of 5f-electrons at high temperatures

The microscopic magnetic properties of the itinerant 5 f -electron antiferromagnet UGa 3 ( T N =67 K) have been investigated in the paramagnetic state by means of Ga NQR studies of the two naturally abundant isotopes 69 Ga and 71 Ga. A striking and unusual increase of the nuclear longitudinal relaxation rate 1/ T 1 has been observed above 230 K, which includes a strong component of nuclear quadrupolar relaxation. Both the magnetic and quadrupolar relaxation rates have been found to increase simultaneously above 230 K. Correspondingly, the NQR frequencies also show a clear deviation from lower- T T 3/2 -dependence above 230 K. These results are discussed in terms of a crossover from lower- T itinerant to higher- T more localized spin fluctuations and associated orbital fluctuations on the part of the U 5 f electrons. A mechanism of transferred quadrupole interaction is presented, through which the fluctuations among the U 5 f orbitals involve those among the counter-anion Ga 4 p orbitals and thereby cause ...

Temperature-Induced Change in the Magnitude of the Effective Density of States: A NQR/NMR Study of the A-Site-Ordered Perovskite System CaCu3Ru4O12

NQR/NMR measurements, including spin–lattice relaxation rate (1/ T 1 ) and Knight shift ( K ) evaluations, have been carried out for Cu and Ru nuclear spins in the A -site ordered perovskite system CaCu 3 Ru 4 O 12 , which exhibits a mass-enhancement-like behavior although it possesses no f electrons. The temperature evolution of T 1 for Cu, which was measured up to 700 K, exhibits 1/ T 1 T = constant behavior at high enough temperatures. This clearly denies the existence of a Cu localized moment, which was previously suggested as the origin of the mass enhancement in a dense Kondo scenario. Furthermore, K and (1/ T 1 T ) for Cu exhibit significant temperature dependences with two characteristic temperatures T F =20 K and T X =180 K, suggesting a temperature-induced transition of microscopic electronic character at T F and T X . We propose a two–band model, where the effective density of states for one of the bands shows a significant temperature dependence in T F < T < T X . Possible origins are discussed.

Ga and Pt NMR Study of UPtGa5 and UNiGa5

Ga and Pt NMR measurements have been carried out for two isomorphs compounds, UPtGa 5 and UNiGa 5 , which exhibit different magnetic structures below T N . Knight shift K measurements in the parama...

Ligand and Actinide NMR Studies in Actinide Oxides and Intermetallic Compounds

In this paper we present highlights from a 6-year program of NMR/NQR/AFNMR studies carried out on both actinide and ligand nuclear spins in oxides and intermetallic compounds of the actinide elements U, Np, and Pu. We begin with the large family of actinide 115 compounds, consisting of metallic antiferromagnets, metamagnets, Pauli paramagnets, and the superconducting Pu-based systems. Short summaries are presented of 69,71 Ga NMR studies of the exotic metamagnet NpCoGa 5 , the surprisingly inhomogeneous UCoGa 5 , and the heavy-fermion “high- T c ” superconductors PuTGa 5 , T=Rh and Co. The case of microdomains in the metallic antiferromagnet UGa 3 is briefly reviewed. Next, we summarize the direct and indirect 235 U NMR studies on USb 2 and URh 3 . These are the first studies of their kind and the only studies of 235 U NMR in a metallic environment. Under the heading of actinide oxides we recap our original studies of 235 U and 17 O NMR in UO 2 , followed by a summary of our investigation of multipolar or...

Direct Observation of 235U NMR in an Itinerant 5f Electron System, USb2

Direct AFNMR studies of 235 U as well as of 121 Sb and 123 Sb nuclear spins have been carried out in the antiferromagnetic state of USb 2 . The central (\(\pm\frac{1}{2}\)) 235 U peak found at 217.2 MHz passes several identification tests, including the expected very low rate of broadening in an applied field. The 235 U hyperfine constant found, 147 T/µ B , is within the expected range. This is the first reported observation of 235 U NMR in a conducting host material.

Physical properties of new superconductor Cd2Re2O7 with pyrochlore-type structure

Abstract 111 Cd NMR study has been performed in the normal state of superconducting pyrochlore oxide Cd2Re2O7. A large orbital susceptibility is identified from K–χ analysis. The sharp decreases of both K and T1−1 below T ∗ suggests a decrease in density of states which is apparently caused by a developing partial energy gap at the Fermi surface.

Thermoelectric power of the superconducting pyrochlore Cd2Re2O7

{}^{69}\mathrm{Ga}

Ga and Pt NMR study of UPtGa5

NMR spectra are reported and analyzed for the paramagnetic and antiferromagnetic (AFM) ordered states of

Hyperfine coupling constant in the paramagnetic and antiferromagnetic states of UGa3

{\mathrm{UGa}}_{3}{(T}_{N}=67\mathrm{K}).