Pt195spin dynamics and Knight shift in single crystals ofUPt<

Abstract

Pt nuclear-magnetic-resonance measurements were performed on aligned single-crystal whiskers of UPt3 for temperatures from 4 to 50 K. A special alignment technique allows us to produce samples with very good c-axis alignment and to work with the field parallel to the c axis with an excellent signal-tonoise ratio. Combining the Knight shift and spin-lattice-relaxation data, we show a continuous crossover from paramagnetic behavior above 40 K toward a degenerate-Fermi-liquid behavior below 5 K.Antiferromagnetic spin fluctuations appear to be responsible for this crossover process, and dominate all low-frequency magnetic properties of this compound. The anisotropy ratios of both the spin-lattice and the spin-spin relaxation rates are found to be temperature independent. Analyzing these ratios we find that the imaginary part of the dynamic spin susceptibility is slightly stronger in the basal plane. I. INTRQDUCTIQN II. SAMPLE PREPARATION AND MEASUREMENTSHeavy-fermion systems have attracted considerable attention since they exhibit unusual physical properties and a variety of ordered states at low temperature. ' For example, in UPt3, superconductivity is found to coexist with antiferromagnetism as inferred from neutronscattering experiments.The static antiferromagnetic order is reported to set in below 5 K. Other neutronscattering experiments ' have revealed the presence of spin fluctuations at higher temperatures. Short-range antiferromagnetic (AFM) correlations were observed between uranium atoms in adjacent basal planes, as were ferromagnetic (FM) correlations between uranium atoms in the same basal plane. These correlations are thought to be responsible for the formation of a coherent electronic state leading to a degenerate Fermi-liquid regime. In light of the possible significance of antiferromagnetic coupling in the superconducting pairing mechanism, it is important to study the temperature region where the crossover to the Fermi-liquid behavior occurs.Nuclear magnetic resonance (NMR) has been an important probe of electronic structure and the low-energy excitations of heavy-fermion metals through the measurements of Knight shift, spectrum linewidth, and nuclearspin relaxation rates. However, ' Pt NMR on a powder sample of UPt3 is difficult to interpret due to the enormous broadening from Knight shift anisotropy. ' We have discovered a way to align the UPt3 whiskers, each of which is a high-quality single crystal, and we have measured anisotropic Knight shifts and relaxation rates in a temperature range of 4 -50 K. These measurements show a continuous crossover from paramagnetic behavior above 40 K toward a degenerate Fermi-liquid behavior below 5 K.Single-crystal whiskers were grown by a method reported previously.The whiskers were less than 40 pm thick and their principal geometric axis is the crystalline c axis. The small thickness of the whiskers allows complete rf penetration at our NMR frequency of 11 MHz throughout the measurement temperature range. The super conducting onset temperature and the transit...

From 3D to 2D: Structural, Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2]δ− Polyanions of the Isotypic MPtAl2 Series (M=Ca–Ba, Eu)

“…The isotropic 195 Pt resonances range between −5509 and −6156 ppm for the TiNiSi representatives, while for LT‐TiPtGe (MgAgAs‐type) δ iso =320 ppm and for TiPtSn (MgAgAs‐type) finally δ iso =470 ppm were reported. Additionally, several binary and ternary uranium platinum intermetallics were investigated, however, no detailed absolute NMR shifts were reported . For details regarding 195 Pt NMR spectroscopy in both solution and solid state, a review by Still and co‐workers is available …”

“…Additionally,s everalb inary and ternary uranium platinum intermetallics were investigated, however, no detaileda bsolute NMR shifts were reported. [101][102][103][104] For detailsr egarding 195 Pt NMR spectroscopy in both solution and solid state, ar eview by Stilla nd coworkers is available. [105] 3.6.…”

Absence of Static Loop-Current Magnetism at the Apical Oxygen Site inHgBa2CuO4+δfrom NMR

“…For example antiferromagnetic ordering has been observed by neutron scattering in UPt 3 [46] but not detected in NMR measurements which was suggested to be a consequence of the effects of thermal fluctuations and different time scales for these experiments. [47,48] Roughly speaking these are 10 −11 s for neutrons,[8] 10 −8 s for µSR, [15] and 10 −6 for NMR frequency shifts. In the context of Hg1201 this was noted by Li et al [12] In summary, we have measured the temperature, field, and angular dependence of the narrow planar and apical 17 O NMR spectra in an underdoped Hg1201 single crystal.…”

Magnetization in the superconducting state of UPt3from polarized neutron diffraction

“…[2] The unusual properties of UPt 3 include development of a heavy fermion state below T = 20 K, [3] dynamic antiferromagnetism that onsets at T N = 6 K, [4][5][6] and an anisotropic superconducting state with three distinct superconducting phases, two of which exist in zero applied magnetic field, [7] Fig. 1.…”