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LaCrGe3 is an itinerant ferromagnet with a Curie temperature of TC=85 K and exhibits an avoided ferromagnetic quantum critical point under pressure through a modulated antiferromagnetic phase as well as tricritical wing structure in its temperature-pressure-magnetic field (T-p-H) phase diagram. In order to understand the static and dynamical magnetic properties of LaCrGe3, we carried out La139 nuclear magnetic resonance (NMR) measurements. Based on the analysis of NMR data, using the self-consistent-renormalization (SCR) theory, the spin fluctuations in the paramagnetic state are revealed to be isotropic ferromagnetic and three dimensional (3D) in nature. Moreover, the system is found to follow the generalized Rhodes-Wohlfarth relation which is expected in 3D itinerant ferromagnetic systems. As compared to other similar itinerant ferromagnets, the Cr 3d electrons and their spin fluctuations are characterized to have a relatively high degree of localization in real space.

LaCrGe3 is an itinerant ferromagnet with a Curie temperature of TC=85 K and exhibits an avoided ferromagnetic quantum critical point under pressure through a modulated antiferromagnetic phase as well as tricritical wing structure in its temperature-pressure-magnetic field (T-p-H) phase diagram. In order to understand the static and dynamical magnetic properties of LaCrGe3, we carried out La139 nuclear magnetic resonance (NMR) measurements. Based on the analysis of NMR data, using the self-consistent-renormalization (SCR) theory, the spin fluctuations in the paramagnetic state are revealed to be isotropic ferromagnetic and three dimensional (3D) in nature. Moreover, the system is found to follow the generalized Rhodes-Wohlfarth relation which is expected in 3D itinerant ferromagnetic systems. As compared to other similar itinerant ferromagnets, the Cr 3d electrons and their spin fluctuations are characterized to have a relatively high degree of localization in real space.

The pressure dependence of the structural, magnetic, and superconducting transitions and of the superconducting upper critical field were studied in sulfur-substituted Fe(Se1-xSx). Resistance measurements were performed on single crystals with three substitution levels (x=0.043, 0.096, 0.12) under hydrostatic pressures up to 1.8 GPa and in magnetic fields up to 9 T and were compared to data on pure FeSe. Our results illustrate the effects of chemical and physical pressure on Fe(Se1-xSx). On increasing sulfur content, magnetic order in the low-pressure range is strongly suppressed to a small domelike region in the phase diagrams. However, Ts is much less suppressed by sulfur substitution, and Tc of Fe(Se1-xSx) exhibits similar nonmonotonic pressure dependence with a local maximum and a local minimum present in the low-pressure range for all x. The local maximum in Tc coincides with the emergence of the magnetic order above Tc. At this pressure the slope of the upper critical field decreases abruptly, which may indicate a Fermi-surface reconstruction. The minimum of Tc correlates with a broad maximum of the upper critical field slope normalized by Tc.

Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN=255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN=236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii) the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. For pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.

We present the results of elastic and inelastic neutron scattering measurements on nonsuperconducting Ba(Fe0.957Cu0.043)2As2, a composition close to a quantum critical point between antiferromagnetic (AFM) ordered and paramagnetic phases. By comparing these results with the spin fluctuations in the low-Cu composition as well as the parent compound BaFe2As2 and superconducting Ba(Fe1-xNix)2As2 compounds, we demonstrate that paramagnon-like spin fluctuations are evident in the antiferromagnetically ordered state of Ba(Fe0.957Cu0.043)2As2, which is distinct from the AFM-like spin fluctuations in the superconducting compounds. Our observations suggest that Cu substitution decouples the interaction between quasiparticles and the spin fluctuations. We also show that the spin-spin correlation length ξ(T) increases rapidly as the temperature is lowered and find ω/T scaling behavior, the hallmark of quantum criticality, at an antiferromagnetic quantum critical point.

Thorough resistivity measurements on single crystals of CeZn11 under pressure p and magnetic field H are presented. At ambient pressure, CeZn11 orders antiferromagnetically at TN=2 K. The pressure dependence of the resistivity reveals an increase of the Kondo effect. We determine the pressure evolution of the magnetic exchange interaction between conduction and localized 4f electrons. It qualitatively reproduces the pressure evolution of the magnetic ordering temperature TO1 (with T O1=TN at ambient pressure). In addition to TO1, a new anomaly TO2 appears under pressure. Both anomalies are found to increase with applied pressure up to 4.9 GPa, indicating that CeZn 11 is far from a pressure induced quantum critical point. Complex T-H phase diagrams are obtained under pressure which reveal the instability of the ground state in this compound. © 2013 American Physical Society.

We report measurements of the resistivity ρ, Sommerfeld coefficient of specific heat γ, and magnetization M of polycrystalline YbAgCu4 in high magnetic fields 0≤B≤18 T [in the case of M(B) to 50 T]. A comparison of the temperature-dependent susceptibility χ(T) as well as field-dependent Sommerfeld coefficient γ and magnetization to Kondo theory for a J=7/2 impurity shows that theory correctly predicts the functional dependence of these quantities on T and B, but the characteristic temperatures determined from the various measurements (120, 98, 77, and 63 K) differ by nearly a factor of 2, which is difficult to understand within the context of Kondo theory even when other possible contributions are considered. In addition the normalized (Wilson) ratio of χ to γ is 1.00 at zero field (compared to 1.14 in Coqblin-Schrieffer theory) and decreases with increasing magnetic field. The magnetoresistance is positive at all temperatures, reaching a value Δρ(B)/ρ(B=0)=0.6 at 25 mK and 18 T. The low-temperature magnetoresistivity Δρ(B) varies as B1.5. We argue that this is dominated by an ordinary impurity effect. Kohler's rule is clearly violated as the temperature is raised; the scattering rate appears to increase with field below 40 K and decrease with field above 40 K. This behavior is expected for an Anderson lattice when a pseudogap is present. At low temperature the resistivity increases as AT2. The coefficient A (corrected for cyclotron-orbit effects) increases with field such that the ratio A(B)/γ(B)2 is a constant. Doping with Lu onto the Yb site, or with Ni onto the Cu site, changes the magnitude of the low-temperature resistivity in a manner consistent with the predictions of the theory of ligand-induced disorder in an Anderson lattice. © 1995 The American Physical Society.

We present resonant ultrasound spectroscopy measurements of the complete elastic moduli of La2-xSrxCuO4 (x=0.00 and 0.14). The x dependence of both the absolute values of the moduli in the tetragonal phase and the temperature dependences of the moduli near the structural phase transition is weak. In both materials c44 and 1/2 (c11-c12) are unaffected by the transition, c33 shows a steplike drop broadened by fluctuations, and c11 and c66 decrease as 1/(T-TSPT) for T>TSPT (where TSPT is the structural phase transition temperature). We also present measurements of the anisotropic thermal expansion coefficients in La1.86Sr0.14CuO4 using a high-resolution capacitance dilatometer. These data when taken together raise serious questions about the standard interpretation of the structural phase transition in La2-xSrxCuO4. © 1994 The American Physical Society.

We report measurements of the temperature dependence of the Bi209 nuclear quadrupole resonance frequency νQ, the Knight shift K, and the spin-lattice relaxation rate 1/T1 in the small-gap semiconductor Ce3Bi4Pt3 between 1.8 and 300 K. Corresponding measurements also are reported for the nonmagnetic metallic isomorph La3Bi4Pt3. The νQ data in the Ce compound show a characteristic departure from metallic-to-insulating behavior when the sample is cooled below TM=80 K, the temperature of the susceptibility maximum, attributable to a loss of low-frequency vibrational modes in the insulating state. The Knight shift has both isotropic and axial components; this anisotropy originates from the presence of Ce via a transferred hyperfine coupling between Ce 4f and conduction electrons. An s-f exchange constant 0.4 eV is found, consistent with hybridization in other rare-earth intermetallic compounds. A change in the scaling between the susceptibility and both the isotropic and axial Knight shifts at temperature TM provides evidence that hybridization between the Ce 4f orbitals and the conduction electrons is responsible for the gap structure. The temperature dependence of the 1/T1 data is consistent with a model electronic density of states possessing a temperature-independent gap δ of 180 K and a bandwidth of the order of 1600 K. The temperature dependence of 1/T1 can also be fit well with a temperature-dependent gap with δ(0) also 180 K. © 1994 The American Physical Society.

A high-resolution photoemission (PES) study of the heavy-fermion compound YbAl3 has been undertaken to test the qualitative and quantitative predictions of the single-impurity model. Corroborating data on YbAgCu4 and YbCu2Si2 are also presented. For Yb-based heavy fermions the model predicts a fully occupied Kondo resonance so that its width, intensity, and temperature dependence should be directly accessible by PES. Due to the existence of temperature- and/or contamination-dependent surface features, which are not dealt with by the model, a rigorous normalization and curve-fitting procedure was required to extract the bulk 4f line shape. For the particular temperature cycling method employed by us, we do not observe any temperature dependence in the peak that had been previously identified as the Kondo resonance. We find that both the binding energy and width of this peak are significantly larger than theory predicts. It is also found that the trends in 4f line shape and surface shift between YbAl3 and LuAl3 are consistent with the trends seen between the 4f core levels of elemental Yb and Lu. Similar results are also found in YbCu2Si2 and YbAgCu4 for similar cycling methods. Recent observations of temperature dependence in these systems are most easily understood in terms of surface phenomena. © 1993 The American Physical Society.

We present valence-band photoemission spectra for CeAl3, CeBe13, CeSi2, CeCu2Si2, and related conventional rare-earth counterpart compounds, taken at photon energies corresponding to the giant 4d resonance with resolution ∼150 meV. We take into account the 5d emission, which comprises 30% of the valence-band emission at the 4d resonance. We compare the resulting 4f emission to the predictions of the Anderson impurity model calculated in a low-order 1/N expansion, and including spin-orbit, crystal-field, and finite Coulomb correlation effects. The calculation gives order-of-magnitude fits to the data, but underestimates the spectral weight near the Fermi level by a factor of 2 and overestimates the width of the main f emission at 2 eV by a factor of 4. We argue that Ce photoemission remains an open problem and discuss several experimental and theoretical issues which need to be resolved to make further progress. © 1993 The American Physical Society.

Ce3Bi4Pt3 is a cerium compound that exhibits a hybridization gap and concomitant semiconducting behavior in the coherent ground state. Using neutron powder diffraction, we have determined the variation of the lattice constant with temperature at two pressures (P=10-3 and 17.7 kbar), and determined the bulk modulus and atomic mean-square displacements for Ce3Bi4Pt3 and its normal analog, La3Bi4Pt3. The thermal expansion Δβ in Ce3Bi4Pt3 exhibits a maximum at Tmax=50 K at ambient pressure. Below 50 K, the bulk modulus ΔB is proportional to TΔβ. We apply a Grüneisen analysis, under the assumption that the free energy exhibits T/T0(V) scaling. The Grüneisen parameter deduced from the ratio ΔB/TΔβ is consistent with the value Ω=36 deduced from the pressure variation of Tmax. The analysis allows us to predict the temperature dependence of the 4f specific heat (ΔCΔβ/Ω), which thus has a maximum at 50 K and a high-temperature entropy nearly equal the expected value R ln6. We argue that the maximum at 50 K reflects an (indirect) hybridization gap of order 100 K. We show further that the lattice constant anomaly Δa0 is proportional to the effective moment Tχ; this suggests that a relationship known to be valid for antiferromagnets, namely (Tχ)/TΔC where ΔC is the specific heat, may be valid for Ce3Bi4Pt3. Finally, we show that the temperature dependence of the mean-square atomic displacements is nearly identical for Ce3Bi4Pt3 and La3Bi4Pt3 and can be fitted by a simple Debye-Waller model; hence the expansion anomaly does not affect the average lattice dynamics. © 1992 The American Physical Society.

Positive-muon (μ+) spin-relaxation experiments have been carried out in a pressed-powder sample of the low-carrier-density heavy-electron system YbBiPt. Spatially inhomogeneous and disordered static Yb magnetism is observed below ∼0.5 K, with a strongly reduced Yb moment of ∼0.1μB over ∼50% of the sample volume at T=0.06 K. Substantial μ+ spin-lattice relaxation, rarely observed in heavy-electron systems, suggests anomalously slow Yb spin fluctuations. Our data are reminiscent of μ+ behavior in spin glasses, and raise the question of whether the large low-temperature specific heat in YbBiPt is due in part to low-lying magnetic excitations. © 1992 The American Physical Society.

X-ray-absorption measurements have been made at the lanthanide L edges, Sr and Cu K edges in the T*-phase La2-x-yRxSryCuO4 compounds with R=Sm, Eu, Gd, Tb, and Dy. The La and rare-earth x-ray-absorption near-edge (XANES) data and the extended x-ray-absorption fine-structure data both clearly indicate that the R and La ions selectively enter the M' site and M site, respectively. The degree of this site ordering is nearly perfect and is similar for the Sm, Eu, Gd, Tb, and Dy members of this family. The L3 XANES data show that the La, Sm, Eu, Gd, and Dy are trivalent in these compounds, but about 20% of the Tb ions are tetravalent in the Tb material. The Cu K-edge XANES spectra are consistent with a divalent state for copper, and are essentially identical for the as-prepared nonsuperconducting samples and the high-pressure oxygenated superconducting counterparts. This indirectly suggests that the hole carrier in the T*-phase superconductors is largely associated with oxygen atoms as in La1.85Sr0.15CuO4. Based on the results of cation-ordering, cation-valence, and oxygen-content measurements, the superconducting behavior of Sm, Em, and Gd T* phases and the lack of superconductivity in the Tb and Dy compounds are discussed. © 1991 The American Physical Society.

Static-susceptibility and thermal-expansion measurements indicate that Ce3Bi4Pt3 is mixed-valent-like, whereas transport measurements reveal a gap of Δ=5 meV in the electronic excitation spectrum. We report the magnetic response of Ce3Bi4Pt3, at temperatures between 2 and 150 K, determined with incident neutron energies of 3.1, 17, and 69 meV. The isostructural, nonmagnetic reference compound La3Bi4Pt3 was also studied at the same temperatures and energies so that phonon contributions could be subtracted accurately. At 2 K, a gap Δm=12 meV is present in the magnetic excitation spectrum: the 3.1-, 17-, and 69-meV data consistently show that the magnetic intensity is zero for energy transfers less than 12 meV, rises sharply between 12 and 20 meV, and falls off smoothly beyond. Above 50 K, the gap in the spin-spin correlation function starts to fill. The neutron results reproduce the temperature dependence of the bulk susceptibility. The relationship between these and other measurements will be discussed. © 1991 The American Physical Society.

Specific-heat, magnetic-susceptibility, and resistivity measurements on annealed polycrystalline samples of CeM2Sn2, with M=Ni, Ir, Cu, Rh, Pd, and Pt, indicate that each of these compounds orders antiferromagnetically at Néel temperatures TN between 0.5 and 4.2 K. Just above TN, all these materials have a significant enhancement of their electronic specific heat, which can be as large as 3-4 J/molK2. We discuss the role of critical fluctuations on the specific heat and argue that the enhancement is associated with a large effective mass and not fluctuations. The anomalously low ordering temperatures and very large electronic specific heat suggest that TN and the Kondo temperature TK are comparable, making these materials particularly attractive for studying the competition between Kondo and Ruderman-Kittel- Kasuya-Yosida interactions. Measurements of the pressure dependence of TN in CeIr2Sn2 were performed to explore this competition, which is discussed in terms of Doniach's Kondo-necklace model. © 1991 The American Physical Society.

We present resistivity (T), susceptibility (T), and specific heat C(T) data for Ce3Bi4Pt3. The susceptibility exhibits a broad maximum centered near 80 K, typical of a somewhat-heavy-electron compound; were the material metallic, a linear coefficient of specific heat =75 mJ/mol Ce K2 would be expected. However, the compound is InotR metallic, as indicated by its resistivity which rises to large values at low temperatures and exhibits activated behavior with an activation energy /kB=35 K. By analogy to SmB6 and YbB12, this energy gap arises from 4f-electron conduction-electron hybridization. Due to the gap, electronic excitations are suppressed at low temperatures and the specific heat is smaller than in nonmagnetic La3Bi4Pt3. Alloying with lanthanum ((Ce1-xLax)3Bi4Pt3) decreases the resistivity and increases the specific heat towards the value expected for the metallic case; i.e., for moderate alloying (x=0.07) the behavior is that of a moderately disordered heavy-electron metal. We argue that lattice periodicity is an essential requirement for the formation of the hybridization gap. © 1990 The American Physical Society.