Physical Review B

Phys. Rev. B 77, 144404 (2008)
63,65Cu NMR and NQR evidence for an unusual spin dynamics in PrCu2 below 100 K
A. Sacchetti, M. Weller, J. L. Gavilano, R. Mudliar, B. Pedrini, K. Magishi, H. R. Ott, R. Monnier, B. Delley, and Y. Onuki
We report the results of a 63,65Cu NMR/NQR study probing the intermetallic compound PrCu2. The previously claimed onset of magnetic order at 65 K, indicated in a muon spin resonance study, is not confirmed. Based on our data, we discuss different possible reasons for this apparent discrepancy, including a non-negligible influence of the implanted muons on their environment. Competing dipolar and quadrupolar interactions lead to unusual features of the magnetic-ion/conduction-electron system, different from those of common intermetallics exhibiting structural or magnetic instabilities.

Phys. Rev. B 77, 144419 (2008)
7Li NMR study of heavy-fermion LiV2O4 containing magnetic defects
X. Zong, S. Das, F. Borsa, M. D. Vannette, R. Prozorov, J. Schmalian, and D. C. Johnston
We present a systematic study of the variations of the 7Li NMR properties versus magnetic defect concentration ndefect within the spinel structure of polycrystalline powder samples (ndefect=0.21, 0.49, and 0.83 mol %) and a collection of small single crystals (ndefect=0.38 mol %) of LiV2O4 in the temperature range from 0.5 to 4.2 K. We also report static magnetization measurements and ac magnetic susceptibility measurements at 14 MHz on the samples at low temperatures. Both the 7Li NMR spectrum and nuclear spin-lattice relaxation rate are inhomogeneous in the presence of the magnetic defects. The 7Li NMR data for the powders are well explained by assuming that (i) there is a random distribution of magnetic point defects, (ii) the same heavy Fermi liquid is present in the samples containing the magnetic defects as in magnetically pure LiV2O4, and (iii) the influences of the magnetic defects and of the Fermi liquid on the magnetization and NMR properties are separable. In the single crystals, somewhat different behaviors are observed, which are possibly due to a modification of the heavy Fermi liquid, to a lack of separability of the relaxation effects due to the Fermi liquid and the magnetic defects, to non-Fermi liquid behavior of the conduction electrons, and/or to quantum fluctuations of finite-size magnetic defects (magnetic droplets). Remarkably, the magnetic defects in the powder samples show evidence of spin freezing below T1.0 K, whereas in the single crystals with similar magnetic defect concentration, no spin freezing was found down to T=0.5 K. Thus, different types of magnetic defects and/or interactions between them appear to arise in the powders versus the crystals, which are possibly due to the substantially different synthesis conditions of the powders and crystals.