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Transition metal dichalcogenides (TMDs) usually show simple structures, however, with interesting properties. Recently some TMDs have been pointed out as type-II Dirac semimetals. In the present work, we investigate the physical properties of a new candidate for type-II Dirac semimetal and investigate the effect of titanium doping on physical properties of Ti-doped single crystalline samples of NiTe2. It was found that this compound shows superconducting properties with a critical temperature close to 4.0 K. Interestingly, applied pressures up to 1.3 GPa have no effect upon the superconducting state. Density Functional Theory (DFT) calculations demonstrate the presence of a Dirac cone in the band structure of NiTe2 literature when Spin-Orbit Coupling (SOC) is included, which is in agreement with a recent report for this compound. Also, our calculations demonstrate that Ti suppresses the formation of these non-trivial states.

Magnetic properties of dilute single crystals of ${\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{\mathrm{B}}_{4}$ ($x=0$, 0.2, and 0.4) were systematically studied. These antiferromagnetic Shastry-Sutherland compounds display a remnant magnetization $M{}_{\mathrm{R}}$ when field cooled below the N\'eel temperature ${T}_{\mathrm{N}}$. The magnitude of $M{}_{\mathrm{R}}$ at low magnetic fields is magnetic field dependent, increasing with increasing magnetic fields, and it saturates for $H\ensuremath{\le}30$ Oe. The ${M}_{R}(T)$ data for both $x\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}0.2$ and 0.4 compositions overlap, and the remnant magnetization follows a universal behavior. We argue that these findings are explained by taking into account the formation of magnetic domains within the crystals, originating from the dilution of a magnetically frustrated, antiferromagnetic sublattice.

We report on thermal conductivity and specific heat measurements for eight UCu4+x Al8−x compounds (0 ≤ x ≤ 2.0) as a function of temperature and magnetic field. For this series of compounds, previous magnetic and transport studies indicated a transition from magnetic to a non-magnetic heavy fermion state near x cr ≈ 1.15. This paper presents supplementary specific heat and thermal conductivity studies. The ratio of the specific heat over temperature C/T data on the non magnetic compound with x cr ≈ 1.15 show logarithmic dependence with T, a hallmark of non-Fermi liquid (NFL) behavior due to the proximity of a quantum critical point. Compounds with higher Cu content (x > x cr ) exhibit unusual temperature scaling in the specific heat possibly due to an increase in disorder between Cu and Al. Thermal conductivity data show stark contrast in the behaviors between the magnetic (x = 0.5) and non-magnetic compound (x = 1.75). Our results confirm that a simple free-electron picture is inadequate for the description of the low-temperature thermal conductivity properties in non-magnetic UCu4+x Al8−x compounds.

We present structural, magnetic, electrical, thermal transport, Hall coefficient, and pressure-dependent resistivity measurements on $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ compounds with $x=0.05$, 0.1, 0.15, 0.2, and 0.3, and $y$ varied between $0\ensuremath{\le}y\ensuremath{\le}0.8$. In order to calculate the ground state, ab initio calculations of the electronic structure of these materials were performed. Our results show that copper intercalation in $\mathrm{ZrT}{\mathrm{e}}_{2}$ induces superconductivity in the $\mathrm{ZrT}{\mathrm{e}}_{2}$ system. For the $\mathrm{C}{\mathrm{u}}_{0.3}\mathrm{ZrT}{\mathrm{e}}_{1.2}$ sample, Hall and Seebeck coefficient measurements show that the system is predominantly negatively charged with carrier density close to ${10}^{19}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}3}$. The temperature dependence of the Hall coefficient, the Seebeck coefficient, and the lower critical field indicates that this material presents multiband character. Pressure-dependent resistivity vs temperature measurements reveal that while the normal-state resistivity decreases with increasing applied pressure, the superconducting transition temperature is completely insensitive to the applied pressure (for pressure in the range 0--1.3 GPa). This suggests that the Fermi gas is intrinsically degenerate under very high pressure, and therefore does not change much with varying external pressure. Finally the band structure calculation shows a dispersion curve containing a bulk three-dimensional Dirac conelike feature at the L point in the Brillouin zone, which is gapless in the absence of spin-orbit coupling, but develops a gap when this coupling is considered. Altogether, the results indicate that the superconducting compound $\mathrm{C}{\mathrm{u}}_{x}\mathrm{ZrT}{\mathrm{e}}_{2\ensuremath{-}y}$ presents a signature of multiband behavior and may possibly be a new example of a topological superconductor.

The face-centered-cubic (fcc) lattice of ${\mathrm{Ru}}^{5+}$ spins in the double perovskite ${\mathrm{Sr}}_{2}{\mathrm{YRuO}}_{6}$ shows a delicate, three-dimensional antiferromagnetic (AFM) ground state composed of stacked square AFM layers. Inelastic neutron scattering data taken on this state reveal a gapped low-energy excitation band emerging from [001] with spin excitations extending to 8 meV. These magnetic excitations are modeled by a simple ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ interaction scheme allowing quantitative comparisons with similar materials. At higher temperatures, the low-energy excitation spectrum is dominated by a quasielastic component associated with size fluctuations of two-dimensional AFM clusters that exhibit asymmetric correlations even at low temperatures. Thus, the fcc lattice in general and the double-perovskite structure in particular emerge as hosts of both two-dimensional and three-dimensional dynamics resulting from frustration.

We report on experimental studies of the Kondo physics and the development of non-Fermi-liquid scaling in UCu4+xAl8−x family. We studied 7 different compounds with compositions between x=0 and 2. We measured electrical transport (down to 65 mK) and thermoelectric power (down to 1.8 K) as a function of temperature, hydrostatic pressure, and/or magnetic field. Compounds with Cu content below x=1.25 exhibit long-range antiferromagnetic order at low temperatures. Magnetic order is suppressed with increasing Cu content and our data indicate a possible quantum critical point at xcr≈1.15. For compounds with higher Cu content, non-Fermi-liquid behavior is observed. Non-Fermi-liquid scaling is inferred from electrical resistivity results for the x=1.25 and 1.5 compounds. For compounds with even higher Cu content, a sharp kink occurs in the resistivity data at low temperatures, and this may be indicative of another quantum critical point that occurs at higher Cu compositions. For the magnetically ordered compounds, hydrostatic pressure is found to increase the Neel temperature, which can be understood in terms of the Kondo physics. For the non-magnetic compounds, application of a magnetic field promotes a tendency toward Fermi-liquid behavior. Thermoelectric power was analyzed using a two-band Lorentzian model, and the results indicate one fairly narrow band (10 meV and below) and a second broad band (around hundred meV). The results imply that there are two relevant energy scales that need to be considered for the physics in this family of compounds.

Temperature-dependent interplane resistivity ${\ensuremath{\rho}}_{c}(T)$ was measured in an isovalent substituted iron-arsenide compound $\text{Ba}({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ru}}_{x}){}_{2}{\mathrm{As}}_{2}$ over a substitution range from parent compound to slightly below optimal doping $x=0.29$. The feature of interest in the ${\ensuremath{\rho}}_{c}(T)$, a broad resistivity crossover maximum found in the parent compound at ${T}_{\text{max}}\ensuremath{\approx}200$ K, shifts to higher temperatures with Ru substitution, $\ensuremath{\sim}340$ K for $x=0.161$ and goes out of the 400 K range for $x=0.29$. Nearly $T$-linear dependence of interplane resistivity is found at the highest substitution level $x=0.29$. This temperature-dependent ${\ensuremath{\rho}}_{c}$ and its evolution with substitution bear close similarity to another type of isovalent substituted system ${\mathrm{BaFe}}_{2}({\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}){}_{2}$. Similarly to the isovalent substitutions, the measurements of interplane resistivity in the parent ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ compound under pressures up to 20 kbar also revealed a rapid rise in ${T}_{\text{max}}$.

The dilute, rare earth bearing family of RT 2 Zn 20 (R = rare earth, T = transition metal) intermetallic compounds can be tuned to a nearly ferromagnetic Fermi liquid that is closer to the Stoner limit than Pd (for R = Y, Lu and T = Fe). The submersion of moment bearing rare earths (Gd–Tm) into this highly polarizable matrix gives rise to exceptionally high temperature ferromagnetism (e.g. T C = 86 K for GdFe 2 Zn 20 ) for a compound with only one moment bearing ion out of 23 in the formula unit. In addition to this d-shell correlated electron behavior, 4f hybridization gives rise to six, new, Yb-based heavy fermion compounds: YbT 2 Zn 20 (T = Fe, Ru, Os, Co, Rh, Ir). These half dozen compounds manifest a range of Yb ion degeneracy values ( N ) for T ∼ T K , ranging from N = 4 – 8 . Not only do these compounds offer a clear testing ground for the effects of low temperature degeneracy on the correlated electron state, they also present an exceptionally clear experimental confirmation of the generalized Kadowaki–Woods formalism.

Electrical transport measurements of the heavy fermion compound YbFe2Zn20 were carried out under pressures up to 8.23 GPa and down to temperatures of nearly 0.3 K. The pressure dependence of the low temperature Fermi-liquid state was assessed by fitting rho(T) = rho_0 + AT^n with n = 2 for T < T_FL. Power law analysis of the low temperature resistivities indicates n = 2 over a broad temperature range for P < 5 GPa. However, at higher pressures, the quadratic temperature dependence is only seen at the very lowest temperatures, and instead shows a wider range of n < 2 power law behavior in the low temperature resistivities. As pressure was increased, T_FL diminished from ~11 K at ambient pressure to ~0.6 K at 8.23 GPa. Over the same pressure range, the A parameter increased dramatically with a functional form of A proportional to (P-Pc)^-2 with Pc~9.8GPa being the critical pressure for a possible quantum critical point.

We report on specific-heat, magnetic-susceptibility, high-field-magnetization, electrical-resistivity, and neutron-diffraction results on UCu3.5Al1.5 ~polycrystal! and UCu3Al2 ~polycrystal and single crystal!. Our results indicate that both compounds crystallize in the hexagonal CaCu5 structure with ordered UCu2 planes separated by planes containing a statistical distribution of Al along with the remaining Cu atoms. At low temperatures, the specific heat and the magnetic susceptibility of both compounds are enhanced, but their temperature dependences are found to be distinct from expectations of Fermi-liquid theory. UCu3.5Al1.5 does not order magnetically, and the low-temperature specific heat and magnetic susceptibility show scaling behavior ~C/T}ln T and x}T 21/3 ! reminiscent of non-Fermi-liquid materials. For UCu3Al2 , on the other hand, the low-temperature scaling of bulk properties is masked by an anomaly around 8‐10 K, which is presumably of magnetic origin. Single-crystal studies of UCu3Al2 reveal a huge magnetic anisotropy with very different in-plane response compared to the c-axis response. Our data provide evidence that any temperature dependence of the magnetic susceptibility ~and electrical resistivity ! of polycrystalline material may be due to averaging anisotropic response over all crystallographic directions. The results are discussed in the context of findings from other non-Fermi-liquid materials. @S0163-1829~96!04641-3#

Author(s): Lawrence, JM; Graf, T; Hundley, MF; Mandrus, D; Thompson, JD; Lacerda, A; Torikachvili, MS; Sarrao, JL; Fisk, Z | Abstract: We present results for the resistivity, the magnetoresistance, and the specific heat of (Formula presented)(Formula presented)(Formula presented) and (Formula presented). The impurity contributions to these measurements follow the predictions of the single-impurity Kondo model for a Kondo temperature (Formula presented)≊65 K, assuming that the impurity behaves as a crystal-field split ((Formula presented)) doublet. Assuming a J=5/2 impurity, the value of (Formula presented) needed to fit these experiments varies from 65 to 125 K. The contribution to the susceptibility may be too small to be explained by the model. These results address whether the nonmagnetic impurity behaves as a Kondo hole. © 1996 The American Physical Society.

We have measured the temperature dependence of the electron paramagnetic resonance (EPR) of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{MnO}}_{3+\mathrm{\ensuremath{\delta}}}$ for 0.0\ensuremath{\le}x\ensuremath{\le}1 at 9.2 and 35 GHz from 270 to 800 K. We vary \ensuremath{\delta} by oxygen and argon annealing. We observe that the intensity of the EPR line decreases exponentially for T above the ordering temperature ${\mathit{T}}_{\mathit{c}}$, with an activation energy which varies with x and \ensuremath{\delta}. We find that the EPR data below \ensuremath{\sim}600 K cannot be attributed to an individual Mn ion of any valency, i.e., ${\mathrm{Mn}}^{2+}$, ${\mathrm{Mn}}^{3+}$, or ${\mathrm{Mn}}^{4+}$ for all annealing conditions. The theoretical models of these ``colossal'' magnetoresistance compounds has not yet focused on the ground-state spin properties, and an interpretation of these data is therefore still lacking. We suggest that the explanation of these EPR data may provide useful tests of the correct model of the magnetization and magnetotransport properties in these compounds. The maximum EPR intensity per formula unit (for ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$${\mathrm{MnO}}_{3}$ air annealed, ${\mathit{T}}_{\mathit{c}}$\ensuremath{\sim}270 K) corresponds to correlated moments with an effective spin of \ensuremath{\sim}30 at T=280 K. \textcopyright{} 1996 The American Physical Society.

We report measurements of the resistivity \ensuremath{\rho}, Sommerfeld coefficient of specific heat \ensuremath{\gamma}, and magnetization M of polycrystalline ${\mathrm{YbAgCu}}_{4}$ in high magnetic fields 0\ensuremath{\le}B\ensuremath{\le}18 T [in the case of M(B) to 50 T]. A comparison of the temperature-dependent susceptibility \ensuremath{\chi}(T) as well as field-dependent Sommerfeld coefficient \ensuremath{\gamma} 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 \ensuremath{\chi} to \ensuremath{\gamma} 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 \ensuremath{\Delta}\ensuremath{\rho}(B)/\ensuremath{\rho}(B=0)=0.6 at 25 mK and 18 T. The low-temperature magnetoresistivity \ensuremath{\Delta}\ensuremath{\rho}(B) varies as ${\mathit{B}}^{1.5}$. 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 ${\mathit{AT}}^{2}$. The coefficient A (corrected for cyclotron-orbit effects) increases with field such that the ratio A(B)/\ensuremath{\gamma}(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.

Neutron diffraction on the double perovskite Sr(2)YRuO(6) with a quasi-fcc lattice of Ru moments reveals planar magnetic correlations that condense into a partial long-range ordered state with coupled alternate antiferromagnetic (AFM) YRuO(4) square layers coexisting with the short-range correlations below T(N1) = 32 K. A second transition to a fully ordered AFM state below T(N2) = 24 K is observed. The reduced dimensionality of the spin correlations is arguably due to a cancellation of the magnetic coupling between consecutive AFM square layers in fcc antiferromagnets, which is the simplest three-dimensional frustrated magnet model system.

We studied the properties of the antiferromagnetic (AFM) UNi0.5Sb2 (TN \approx 161 K) compound in Sb-flux grown single crystals by means of measurements of neutron diffraction, magnetic susceptibility ({\chi}), specific heat (Cp), thermopower (S), thermal conductivity ({\kappa}), linear thermal expansion ({\Delta}L/L), and electrical resistivity ({\rho}) under hydrostatic pressures (P) up to 22 kbar. The neutron diffraction measurements revealed that the compound crystallizes in the tetragonal P42/nmc structure, and the value of the U-moments yielded by the histograms at 25 K is \approx 1.85 \pm 0.12 {\mu}B/U-ion. In addition to the features in the bulk properties observed at TN, two other hysteretic features centered near 40 and 85 K were observed in the measurements of {\chi}, S, {\rho}, and {\Delta}L/L. Hydrostatic pressure was found to raise TN at the rate of \approx 0.76 K/kbar, while suppressing the two low temperature features. These features are discussed in the context of Fermi surface and hybridization effects.

Single crystals of Ba(Fe${}_{1\ensuremath{-}x}$Mn${}_{x}$)${}_{2}$As${}_{2}$, $0lxl0.148$, have been grown and characterized by structural, magnetic, electrical transport, and thermopower measurements. Although growths of single crystals of Ba(Fe${}_{1\ensuremath{-}x}$Mn${}_{x}$)${}_{2}$As${}_{2}$ for the full $0\ensuremath{\leqslant}x\ensuremath{\leqslant}1$ range were made, we find evidence for phase separation (associated with some form of immiscibility) starting for $xg0.1$--0.2. Our measurements show that whereas the structural/magnetic phase transition found in pure BaFe${}_{2}$As${}_{2}$ at 134 K is initially suppressed by Mn substitution, superconductivity is not observed at any substitution level. Although the effect of hydrostatic pressure up to 20 kbar in the parent BaFe${}_{2}$As${}_{2}$ compound is to suppress the structural/magnetic transition at the approximate rate of 0.9 K/kbar, the effects of pressure and Mn substitution in the $x=0.102$ compound are not cumulative. Phase diagrams of transition temperature versus substitution concentration $x$ based on electrical transport, magnetization, and thermopower measurements have been constructed and compared to those of the Ba(Fe${}_{1\ensuremath{-}x}$TM${}_{x}$)${}_{2}$As${}_{2}$ (TM= Co and Cr) series.

The $ab$ plane resistivity of Ba(Fe${}_{1\ensuremath{-}x}$Ru${}_{x}$)${}_{2}$As${}_{2}$ ($x=0.00$, 0.09, 0.16, 0.21, and 0.28) was studied under nearly hydrostatic pressures, up to 7.4 GPa, in order to explore the $T\ensuremath{-}P$ phase diagram and to compare the combined effects of isoelectronic Ru substitution and pressure. The parent compound BaFe${}_{2}$As${}_{2}$ exhibits a structural/magnetic phase transition near 134 K. At ambient pressure, progressively increasing Ru concentration suppresses this phase transition to lower temperatures at an approximate rate of $\ensuremath{\sim}$5 K/% Ru correlated with the emergence of superconductivity. By applying pressure to this system, a similar behavior is seen for each concentration: the structural/magnetic phase transition is further suppressed and superconductivity induced and ultimately, for larger $x$ Ru and $P$, suppressed. A detailed comparison of the $T\ensuremath{-}P$ phase diagrams for all Ru concentrations shows that 3 GPa of pressure is roughly equivalent to $10%$ Ru substitution. Furthermore, due to the sensitivity of Ba(Fe${}_{1\ensuremath{-}x}$Ru${}_{x}$)${}_{2}$As${}_{2}$ to pressure conditions, the melting of the liquid media, $4:6$ light mineral oil : $n$-pentane and $1:1$ isopentane : $n$-pentane, used in this study could be readily seen in the resistivity measurements. This feature was used to determine the freezing curves for these media and to infer their room temperature, hydrostatic limits: 3.5 and 6.5 GPa, respectively.

This paper presents a review of the electronic structure of Y1−xUxPd3, along with new data on Fermi level tuning in alloy and in Th1−xUxPd3.

The intermetallic UCu4+xAl8−xcompounds (0.1⩽x⩽1.95) have remarkable electronic and magnetic properties. The Cu-poor compositions within this x-range are antiferromagnetic (AF). The Neel temperature (TN) drops gradually from ≈36 K for x=0.1 until AF is completely suppressed near x=1.1, while the Sommerfeld coefficient (γ) increases dramatically with x, reaching a maximum value of 750 mJ/mol K2 for x=1.75. Reported in this investigation are magnetoresistance (MR) and magnetic susceptibility (χ) measurements at low temperatures (T) and high magnetic fields (B). The isothermal MR data below 40 K crosses over from positive in the low-x to negative in the high-x range. These results are interpreted in the context of spin fluctuations, hybridization, and non-magnetic atomic disorder.

This work reports on the phase diagram study of the dense Kondo system CeB 6 by means of magnetization ( M ) and transverse magnetoresistance (MR) measurements in magnetic fields ( B ) to 18 T, in the temperature ( T ) range from 1.8 to 40 K. The zero field resistivity displays Kondo behavior in the paramagnetic P-phase, while two discontinuities at low T were observed at T Q ≈3.5 K and T N ≈2.3 K, the boundaries of the antiferro-quadrupolar (AFQ), and antiferromagnetic (AF) phases, respectively. The isothermal transverse MR is large and negative at low T , and it shows a distinct feature when the P–AFQ line of the B – T phase diagram is crossed. Similarly, the M vs. B curves at low temperatures show upward discontinuities at the phase boundary. Both the features in MR and M at the P–AFQ line correlate well in T , revealing the gradual increase of the T for the onset of AFQ ordering with B . No evidence for reentrant behavior could be observed in fields to 18 T.

For x≤0.3 in the alloy system Y 1-x U x Pd 3 , transport data display signatures of Kondo behavior with the Kondo temperature increasing as x decreases. For the same range of x, the inverse photoemission spectrum shows a growth of U 5f spectral weight near the Fermi energy. We interpret this Fermi-energy weight as the first identification of the Kondo resonance in a uranium material

We have performed a neutron-scattering investigation of the heavy-fermion compound ${\mathrm{Uru}}_{1.2}$${\mathrm{Re}}_{0.8}$${\mathrm{Si}}_{2}$, in order to verify the existence of long-range ferromagnetic order and characterize the properties of the ordered phase. This study consisted of measurements of elastic scattering using polarized and unpolarized neutrons, measurements of low-angle critical scattering, and the determination of the temperature (T) dependence of the order parameter. The critical scattering measurements at wave vector Q=0.08 A\r{} $^{\mathrm{\ensuremath{-}}1}$ revealed a sharp peak at T\ensuremath{\approxeq}30 K, which was taken as the Curie temperature ${\mathit{T}}_{\mathit{C}}$. The value of the ordered moment estimated from the elastic-scattering data is \ensuremath{\approxeq}0.49${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 10 K, which is in good agreement with the value of 0.46${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ obtained previously from magnetization measurements. A polarized-neutron beam elastically scattered off the {112} planes was only partially depolarized upon traveling through the sample. The partial depolarization of the beam suggests that ${\mathrm{URu}}_{1.2}$${\mathrm{Re}}_{0.8}$${\mathrm{Si}}_{2}$ is either a weak ferromagnet, or that the domains are extremely small. Extensive short-range correlations precede the onset of long-range order. Preliminary results of inelastic scattering are discussed.

The effects of pressure generated in a liquid-medium clamp pressure cell on the in-plane and $c$-axis resistance, temperature-dependent Hall coefficient, and low-temperature magnetoresistance in ${\text{CaFe}}_{2}{\text{As}}_{2}$ are presented. The $T\ensuremath{-}P$ phase diagram, including the observation of a complete superconducting transition in resistivity delineated in earlier studies is found to be highly reproducible. The Hall resistivity and low-temperature magnetoresistance are sensitive to different states/phases observed in ${\text{CaFe}}_{2}{\text{As}}_{2}$. Auxiliary measurements under uniaxial $c$-axis pressure are in general agreement with the liquid-medium clamp cell results with some difference in critical pressure values and pressure derivatives. The data may be viewed as supporting the potential importance of nonhydrostatic components of pressure in inducing superconductivity in ${\text{CaFe}}_{2}{\text{As}}_{2}$.

Analyse par diffusion inelastique des neutrons. La variation de la largeur en energie du spectre vis-a-vis de la temperature suit une loi d'Arrhenius sur une large gamme de temperatures. La largeur au-dessus de la temperature d'etat de verre de spin est beaucoup plus grande que pour d'autres verres de spin concentres

Recent investigations of the superconducting iron-arsenide families have highlighted the role of pressure, be it chemical or mechanical, in fostering superconductivity. Here we report that CaFe2As2 undergoes a pressure-induced transition to a nonmagnetic volume "collapsed" tetragonal phase, which becomes superconducting at lower temperature. Spin-polarized total-energy calculations on the collapsed structure reveal that the magnetic Fe moment itself collapses, consistent with the absence of magnetic order in neutron diffraction. © 2008 The American Physical Society.

The effects of pressure up to $\ensuremath{\sim}20\text{ }\text{kbar}$ on the structural phase transition of ${\text{SrFe}}_{2}{\text{As}}_{2}$ and lightly Sn-doped ${\text{BaFe}}_{2}{\text{As}}_{2}$ as well as on the superconducting transition temperature and upper critical field of $({\text{Ba}}_{0.55}{\text{K}}_{0.45}){\text{Fe}}_{2}{\text{As}}_{2}$ single crystals have been studied. All the transition temperatures decrease with pressure in an almost linear fashion. Under pressure, the upper critical-field curve ${H}_{c2}(T)$ for $({\text{Ba}}_{0.55}{\text{K}}_{0.45}){\text{Fe}}_{2}{\text{As}}_{2}$ shifts down in temperature to follow the zero-field ${T}_{c}$ with very little change in slope. Composite $P\text{\ensuremath{-}}T$ phase diagrams for three parent compounds $A{\text{Fe}}_{2}{\text{As}}_{2}$ ($A=\text{Ba}$,Sr,Ca) are constructed and appear to be remarkably similar: (i) having a structural (antiferromagnetic) phase-transition line with a negative slope and (ii) showing signs of the emerging superconducting state at intermediate pressures.

We studied single-crystalline ${\mathrm{Pr}}_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_{3}$ by means of measurements of magnetic susceptibility and specific heat at ambient pressure $(P)$ and electrical resistivity $(\ensuremath{\rho})$ in hydrostatic pressures up to $2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. This material displays ferromagnetic (FM) order, with Curie temperature ${T}_{C}\ensuremath{\approx}255\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. A crystallographic transformation from $I4∕mcm$ to $Fmmm$ is accompanied by the onset of antiferromagnetism (AFM), with N\'eel temperature ${T}_{N}\ensuremath{\approx}161\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The effect of pressure is to lower ${T}_{C}$ and to raise ${T}_{N}$ at the approximate rates of $\ensuremath{-}3.2$, and $14.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{GPa}$, respectively. Although the value of ${T}_{N}$ increases with $P$, due to the enhancement of the superexchange interactions, the AFM-$Fmmm$ state is progressively suppressed, as pressure stabilizes the FM-$I4∕mcm$ phase to lower temperatures. The $\ensuremath{\rho}$ vs $T$ data suggest that the AFM phase should be completely suppressed near $2.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.

We studied the effect of hydrostatic pressure (P) on the structural phase transitions and superconductivity in the ternary and pseudo-ternary iron arsenides CaFe2As2, BaFe2As2, and (Ba0.55K0.45)Fe2As2, by means of measurements of electrical resistivity (rho) in the 1.8 - 300 K temperature (T) range, pressures up to 20 kbar, and magnetic fields up to 9 T. CaFe2As2 and BaFe2As2 (lightly doped with Sn) display structural phase transitions near 170 K and 85 K, respectively, and do not exhibit superconductivity in ambient pressure, while K-doped (Ba0.55K0.45)Fe2As2 is superconducting for T < 30 K. The effect of pressure on BaFe2As2 is to shift the onset of the crystallographic transformation down in temperature at the rate of about -1.04 K/kbar, while shifting the whole rho(T) curves downward, whereas its effect on superconducting (Ba0.55K0.45)Fe2As2 is to shift the onset of superconductivity to lower temperatures at the rate of about -0.21 K/kbar. The effect of pressure on CaFe2As2 is first to suppress the crystallographic transformation and induce superconductivity with onset near 12 K very rapidly, i.e., for P < 5 kbar. However, higher pressures bring about another phase transformation characterized by reduced resistivity, and the suppression of superconductivity, confining superconductivity to a narrow pressure dome centered near 5 kbar. Upper critical field (Hc2) data in (Ba0.55K0.45)Fe2As2 and CaFe2As2 are discussed., 6 pages - submitted to SCES-08 - Proceedings will appear in Physica B

Low temperature ( 1.5 – 4.2K ) ESR experiments of diluted S(Gd3+) and non-S(Dy3+, Er3+) rare-earths (REs) in single crystals of the semiconducting compound CeFe4P12 show that the REs impurities are located in cubic sites, substituting probably the Ce atoms. Although metallic-like resonance shapes were observed in all cases, the measured g-values, hyperfine constants and temperature dependence of the linewidth, seem to indicate the absence of exchange interaction between the localized RE's magnetic moment and the host's conduction electrons. Doped and undoped samples all show extra anisotropic lines which were tentatively attributed to defects associated to Ce3+ ions located at sites of lower symmetry.

We have investigated the interesting alloy system Ce(Ru{sub 1{minus}{ital x}}Rh{sub {ital x}}){sub 3}B{sub 2}, where the physical properties change from superconducting to ferromagnetic as {ital x} changes from 0 to 1. We report the results of transport, magnetic, crystallographic, and electron-spectroscopy measurements, and a theoretical analysis of the electron-spectroscopy data using the impurity Anderson Hamiltonian applied to the Ce 4{ital f} electrons. Superconductivity exists in the range 0{lt}{ital x}{lt}0.38, while ferromagnetism occurs in the range 0.84{lt}{ital x}{lt}1. Our studies of superconductivity and ferromagnetism in Ce(Ru{sub 1{minus}{ital x}}Rh{sub {ital x}}){sub 3}B{sub 2} show that ferromagnetism is associated with nearly trivalent Ce ions. We find that the alloying mechanism controlling the low-energy properties of this system is the transition-metal 4{ital d} density of states at the Fermi level, rather than any parameter directly connected to the 4{ital f} states, such as its binding energy, Coulomb interaction, or the average hybridization strength between the localized 4{ital f} and conduction electrons. We use this result to further elucidate our previously proposed exchange split-Kondo resonance model of the ferromagnetism near {ital x}=1.

Analyse theorique des donnees de spectroscopie electronique des supraconducteurs a fermion lourd, selon le modele de l'impurete de Anderson. Les spectres sont generalement en accord avec une description de liquide de Fermi de Kondo de ce materiau

Specific heats were measured in the range 0.3 ⩽T⩽30 K for 0⩽H⩽7T and P=0, and for H=0 and 0⩽P⩽6.3 kbar. For H=0 and P=0, the measurements were extended to 0.15K. Above the superconducting transition the H=0 and 7T data can be superimposed. For the magnetic transition near T0 = 18K, T0 increased with increasing P accompanied by a broadening and attenuation of the specific heat anomally. The superconducting transition near Tc = 1.5 K was broadened, attenuated and shifted to lower temperatures for both increasing P and H. The superconducting transition is similar to that of UPt3, and both the temperature dependence of the superconducting state specific heat and the derived parameters are consistent with an unconventional polar-type pairing.

We have performed a neutron scattering study of the heavy fermion compound URu 1.2 Re 0.8 Si 2 , in order to verify the occurrence of long range ferromagnetic order. This study consisted of measurements of elastic, inelastic, and polarized neutron scattering, measurements of low angle critical scattering, and the determination of the temperature dependence of the order parameter. We found (1) a sharp peak in the critical scattering at ≈30 K for the wave vector Q = 0.08 A −1 , and (2) an enhancement of the intensity at the position of the {1 0 1} nuclear Bragg reflection below the Curie temperature. These measurements suggest the occurrence of long range magnetic order. The value of the ordered magnetic moment is estimated to be ≈(0.49±0.05)μ B at 10 K, in good agreement with the 0.46μ B value obtained from magnetization measurements.

Ce compose presente deux transitions de phase electroniques aux basses temperatures. On etudie l'effet d'une substitution chimique de metaux de transition au moyen de l'analyse des variations de la resistivite electrique, de la susceptibilite magnetique et de la chaleur specifique dans URu 2−x M x Si 2 pour x≤0,2

Neutron-diffraction results on single crystalline UFe 4 P 12 are reported. The structural parameters of UFe 4 P 12 have been determined at 15 K. Below 3.1 K, we find that there is an additional magnetic contribution on top of nuclear reflections at higher d spacings. An intensity analysis of the magnetic contributions corroborates a ferromagnetic ground state with U moments only. It is argued that this compound forms three magnetic domains with an upper limit of about 0.5 μ B (at 2.8 K) for the U moment.

We carried out an investigation of the effect of quasi‐hydrostatic pressures up to 1.2 GPa in pure and Rh‐doped RuSr2GdCu2O8 compounds, by means of measurements of electrical resistivity in magnetic fields up to 9 T. The onset temperatures for superconductivity, and for magnetic order in the undoped RuSr2GdCu2O8 compound are Tc ≈ 50 K, and Tm ≈ 133 K, respectively. The partial substitution of Rh for Ru lowers both these transitions temperatures. However, the effect of pressure for all compositions studied, up to 10% substitution, was to increase both Tc, and Tm. The effect of pressure on the upper critical magnetic field of the pure, and Rh‐doped compounds is discussed.

The compound of RuSr2GdCu2O8 shows distinct magnetic transitions, which occur on independent sublattice. Comparison is made between measurements in the cell at no pressure and maximum 10 kbar of quasi‐hydrostatic pressure. The chain site ruthenium oxide layer has a weakly ferromagnetic transition of 133 K and increases to 139 K under pressure. The plane site copper oxide layer has an intra‐granular superconducting critical temperature of 49 K and increases to 51 K under pressure. The response to pressure is related to anisotropic changes in lattice parameters. The bulk or inter‐granular superconducting transition also shows a significant increase with applied pressure. With low frequency (0.2Hz) AC susceptibility, the peak in the imaginary component increases from 21 K to 24 K under pressure.

Heavy fermion compounds represent one of the most strongly correlated forms of electronic matter and give rise to low temperature states that range from small moment ordering to exotic superconductivity, both of which are often in close proximity to quantum critical points. These strong electronic correlations are associated with the transfer of entropy from the local moment degrees of freedom to the conduction electrons, and, as such, are intimately related to the low temperature degeneracy of the (originally) moment bearing ion. Here we report the discovery of six closely related Yb-based heavy fermion compounds, YbT 2 Zn 20 , that are members of the larger family of dilute rare earth bearing compounds: RT 2 Zn 20 (T = Fe, Co, Ru, Rh, Os, Ir). This discovery doubles the total number of Yb-based heavy fermion materials. Given these compounds' dilute nature, systematic changes in T only weakly perturb the Yb site and allow for insight into the effects of degeneracy on the thermodynamic and transport properties of these model correlated electron systems.

We have measured transverse (B ⊥ I) and longitudinal (B ∥ I) magnetoresistance on a single crystalline sample of YbNi2B2C. A remarkably large anisotropic transverse magnetoresistance was found when applying magnetic field parallel or perpendicular to the c-axis of the tetragonal crystallographic structure. A pronounced maximum at 10 T develops below 4 K in the transverse magnetoresistance when the magnetic field is applied along the c-axis, whereas a minimum is found at 7 T below 4 K when the applied field is perpendicular to the c-axis. Above 5 K both configurations (B ∥c and B ⊥ c) show a negative magnetoresistance. Finally, the possibility of a metamagnetic-like transition in this compound will be discussed in conjunction with high field magnetization experiments.

We report measurements of the isothermal magnetization of U1−xThxBe13 at 2.5 K, in fields to 18 T, on samples where 0 ⩽ x ⩽ 1. Linear (χ1) and nonlinear (χ3) contributions to the susceptibility are extracted from the data and studied as a function of thorium concentration x. We find χ3 to be independent of x to about x = 0.9 while χ1 shows an upturn as x → 1, an upturn which we interpret as a reduction in a cooperative Kondo like compensation of the uranium magnetic moments.

The electrical resistivity (ρ{variant}) and magnetoresistance of polycrystalline YbAgCu4 have been measured at temperatures between 25 mK and 300 K, and at magnetic fields (B) up to 18 T. The magnetoresistance (ρ{variant}(B) - ρ{variant}(0))/ρ{variant}(0)) is positive at all temperatures below 200 K and reaches its maximum of 60% at 18 T and 25 mK. The field- and temperature-dependent resistivity does not scale in a simple way. The opposite sign of the magnetoresistance at ambient and high pressure can be explained qualitatively by crystal-field effects lifting the degeneracy of the J = 7 2 groundstate. The linear coefficient of the specific heat (γ) measured at fields up to 10 T shows a quadratic field dependence. We did not find a linear relation between γ2 and A, the T2-coefficient of the temperature-dependent resistivity, with the applied magnetic field as the implicit parameter. © 1995.

Neutron diffraction and magnetization measurements as a function of applied magnetic field are reported for single crystal UNi 2 Si 2 . The combined results are used to construct a magnetic phase diagram for applied fields along c . The simple body-centered antiferromagnetic phase, stable in zero field from 55 K to 103 K, is suppressed completely by fields greater than 3.8 T. There is a reentrant triple point at 102.8 K and 2.1 T.

We report magnetic susceptibility, neutron, and x‐ray diffraction measurements on polycrystalline UAu2Si2. Magnetic susceptibility data show the existence of two phases below 50 K. Since no superlattice neutron peaks were observed within the sensitivity of the apparatus we conclude that the system is not a canted ferromagnet, as was suggested earlier. On the basis of the temperature dependence of the neutron and x‐ray intensity we discuss a possibility that UAu2Si2 undergoes two structural phase transitions, at 48 and at 18 K and that these transitions are correlated with the magnetic state of the material.

We report neutron diffraction measurements on a single crystal of UNi2 Si2. Three magnetically ordering phases are observed below 123 K with the magnetic moment parallel to the c‐axis in all three phases. The low temperature (T