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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 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.

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#

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.

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.

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 ${\text{CaFe}}_{2}{\text{As}}_{2}$.

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.

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

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.

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

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.

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

Magnetization measurements performed on UCu2Si2 and UNi2Si2 are reported. The compound UCu2Si2 appears to undergo both an antiferromagnetic (AFM) transition at T≊107 K and a ferromagnetic (FM) transition at Tc≊103 K. While the second transition at Tc has already been reported, the AFM phase was apparently overlooked in earlier studies. The compound UNi2Si2 undergoes a transition at T≊97 K, which was previously shown to be AFM by neutron scattering; we present evidence for the occurrence of a FM state below the AFM transition.

Measurements and analysis of the paramagnetic susceptibility of La1-xCaxMnO3+y (0 ≤ x ≤ 1) are reported. The magnetization was also measured in large fields (H ≤ 18 tesla) for a specimen of La0.79Ca0.21MnO3+y. The paramagnetic susceptibility is observed to be strongly enhanced for most compositions studied, including a number of antiferromagnetic compositions. This behavior is attributed to the existence of magnetic polarons.

Low-teperature specific-heat C measurements have been made on the high-T/sub c/ superconductors RBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ (R = Nd, Sm, Gd, Dy, and Er; deltaapprox. =0.1) for 0.5approx.

The upper critical magnetic field of EuMo/sub 6/S/sub 8/ in its high-pressure superconducting phase was measured resistively at 16 kbar in dc magnetic fields to 28 T. The data can be described by multiple pair-breaking theory including a negative exchange field due to the Eu/sup 2 +/ ions that acts on the superconducting electrons. Measurements of the ac heat capacity of EuMo/sub 6/S/sub 8/ above approx.13 kbar revealed that the compound exhibits bulk superconductivity, but no Meissner effect was observed in magnetization measurements.

The pressure dependences of the structural and superconducting transition temperatures (T/sub s/ and T/sub c/, respectively) of a melted high-quality sample of EuMo/sub 6/S/sub 8/ have been measured under nearly hydrostatic pressure up to approx.15 kbar. Applied pressure (P) depresses T/sub s/ rapidly from T/sub s/ 109 K at zero pressure to T/sub s/ = 0 just below 13 kbar where the slope dT/sub s//dP is nearly vertical. A very sharp superconducting transition is observed above 13 kbar; at 13.2 kbar, T/sub c/ = 12.2 K and has a width ..delta..T/sub c/ = 0.03K. Above 13 kbar, T/sub c/ decreases nearly linearly with pressure at a rate dT/sub c//dP = -0.18 K/kbar, which is comparable to that observed for other superconducting Chevrel-phase compounds. The upper critical magnetic field H/sub c/2 as a function of temperature was measured up to 8 T and displays features that are indicative of the exchange-field compensation effect.

The effect of nearly hydrostatic pressure to 20 kbar on the superconducting transition temperature Tc of (Y1−χPrχ)Ba2Cu3 O7−δ compounds with 0⩽χ⩽0.5 was determined by means of low frequency ac electrical resistivity measurements. The application of pressure to this system reveals striking effects which appear to be associated with the hybridiazation between Pr 4f and valence band states. In this range of pressure P, Tc increases with P for 0⩽χ⩽0.2, exhibits a maximum at ∼6 kbar for χ=0.3, and decreases rapidly with P for χ⩾0.4, while the initial rate of increase of Tc with pressure (dTc/dP)P=0, increases with χ for 0⩽χ⩽0.3. These results suggest there is a pressure-induced electronic phase transition at ∼6 kbar foir χ=0.3 that shifts to lower values of P for higher values of χ.

The new compound UFe4P12, which was found to be isostructural to superconducting LaFe4P12 and have a lattice constant of 7.7729 A, is a semiconductor and shows ferromagnetic order below 3.15 K. CeFe4P12 is also a semiconductor, and its magnetic susceptibility is unusually small in comparison to LaFe4P12. The semiconducting behaviors of both UFe4P12 and CeFe4P12 seem anomalous and may arise from strong f‐electron hybridization.

The magnetic susceptibility χ of CeT3B2 and UT3B2 compounds (T=Co, Ru, and Ir) has been measured as a function of temperature T for 2 K≤T≤300 K. For each sample, χ is weakly temperature dependent above ∼100 K, and approaches a finite value as T→0, indicative of a nonmagnetic ground state. The intrinsic susceptibility χ0, after correcting for the effect of the impurities at low temperature, ranges from 5.05×10−4 cm3/mole for CeRu3B2 to 1.33×10−3 cm3/mole for UIr3B2. The ratio S=π2k2Bχ0/3μ2Bγ (γ is the electronic specific heat coefficient), a rough gauge of exchange enhancement, ranges from 0.9 for CeIr3B2 to 4 for CeCo3B2.

Superconducting and magnetic properties of La1.2−xEuxMo6S8 pseudoternary compounds were investigated by means of low‐frequency ac and dc magnetic susceptibility measurements under hydrostatic pressure up to 20 kbar and in magnetic fields up to 10 T. At atmospheric pressure, the superconducting transition temperature Tc is a weak function of Eu concentration x for 0?x?0.2, and decreases smoothly with x for x≳0.2, until it vanishes for x≳0.95. Hydrostatic pressure was found to lower Tc in the La‐rich compounds and to increase Tc in the Eu‐rich compounds. Pressure also induces superconductivity in compounds with x≳0.95 which are not superconducting at atmospheric pressure with maximum Tc’s that are quite high (∼8 K, midpoint) and comparable to the Tc values of other ternary molybdenum sulfides with divalent metal atoms. Magnetization data (dc) on a La0.2Eu1.0Mo6S8 compound revealed a sizable Meissner effect for pressures ≳7 kbar. At atmospheric pressure, the upper critical magnetic field Hc2 for 0

The compound CeOs2 has been prepared in both cubic C15 and hexagonal C14 Laves phases. Measurements of ac and dc magnetic susceptibility, electrical resistivity, and specific heat have been performed on samples of both phases. The C14 phase has been found to exhibit superconductivity with a superconducting transition temperature Tc of 1.1 K, while the C15 phase does not display superconductivity above 70 mK. The curves of resistivity vs temperature for both phases exhibit strong negative curvature which are reminiscent of valence fluctuation compounds.

We report evidence which suggests surface ferromagnetism in a ferromagnetic superconductor arising from the competition between the Meissner current shielding effect and the fluctuations of the localized magnetic moments. We have measured the surface impedance penetration depth Λ of ErRh4B4 and Er0.5Ho0.5Rh4B4 by employing a spectrometer operated at 9 GHz. For ErRh4B4, owing to the critical spin fluctuations just above Ts (>Tc2), the critical temperature at which surface ferromagnetism appears, Λ−1 decreases smoothly as temperature decreases toward Ts. For Er0.5Ho0.5Rh4B4, the decrease of Λ−1 arising from spin fluctuations for T>Tc2 is very small, and Λ−1 decreases abruptly at Tc2. We will discuss the theory and show how the predicted values of Λ(T) compare well with the observed values.

A large class of ternary Mo chalcogenides can be formed with the general formula MxMo6X8 where M is a metal, 0 ≤ x ≤ 4, and X = S, Se or Te (1). These compounds have a relatively complex crystal structure with rhombohedral symmetry and a rhombohedral angle that is close to 90° (2). The crystal structure of the ternary Mo chalcogenides (Chevrel phases) is shown in Fig. 1 for a compound with the formula REMo6S8 (RE = rare earth).

We have investigated two antiferromagnetic superconductors, NdRh4B4 and SmRh4B4, which exhibit two quite different temperature dependencies of the upper critical field arising from two different mechanisms1 of the modification of superconductivity by the presence of antiferromagnetism. In order to further study these mechanisms, we have investigated the electromagnetic properties and have measured the penetration depths λ(T) of NdRh4B4 (Tc=5.45 K, TN1=1.31 K, and TN2=0.89 K) and SmRh4 B4 (Tc=2.2 K, TN=0.9 K), employing a tunnel diode oscillator at ∼30 MHz. Above the antiferromagnetic transition temperature (TN1 for NdRh4B4 and TN for SmRh4B4), the temperature dependencies of the penetration depths of these two superconductors fit the BCS theory well. We have found λ(0)=2170 and 980 A for NdRh4B4 and SmRh4B4, respectively. However, as temperature is lowered, λ(T) for NdRh4B4 increases near TN1 and then saturates near TN2, presumably owing to the molecular field effect.2 The spin‐fluctuation effects,2 expec...

Superconductivity with critical transition temperature Tc near 90 K has been found in RBa2Cu3O7-δ compounds where R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and with Tc=56 K for R = La by electrical resistivity and low field magnetic susceptibility measurements. All compounds (except La) form in the orthorhombic, layered perovskite structure which is isomorphic to YBa2Cu3O7-δ. The lattice parameters of the compounds decrease in accordance with the metallic radii of the R trivalent ions. The electrical resistivity of the compounds studied (except for R = Nd) decreases with decreasing temperature and exhibit a sharp superconducting transition. Upper critical magnetic field Hc2 of the heavy R compounds (R from Dy to Yb) were measured and the highest initial slope |dHc2/dTc|Tc yet found for above 90 K superconductors was exhibited in TmBa2Cu3O7-δ with a value of 2.8 tesla/K.