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The pressure dependence of the static magnetic susceptibility χ(T) of the heavy-electron superconductor UBe13 was investigated over temperatures ranging from 1.5 to 300 K and at pressures from 1 bar to 8 kbar. It is linear in pressure over the full temperature range, having a small constant pressure dependence at higher temperatures that increases rapidly below about T=150 K. The maximal value of the relative susceptibility change [1/χ(dχ/dP)] is about 1% per kbar. The Curie-Weiss law is obeyed in the temperature range 100 to 300 K with the effective magnetic moment peff=3.46μB independent of pressure, while the paramagnetic Curie temperature FTHETA∼-100 K becomes more negative with pressure. The lattice parameter of cubic UBe13 was measured as a function of pressure, permitting a determination of a compressibility value of -9.2×10-4 kbar-1 near ambient pressure. The pressure dependence of χ(T) is significantly weaker than that of the specific-heat coefficient C(T)/T; we discuss whether this can be resolved by (i) consideration of intersite antiferromagnetic interactions, or (ii) the quadrupolar Kondo-effect model, and conclude that the latter provides a stronger explanation of the results. © 1993 The American Physical Society.

The pressure dependence of the static magnetic susceptibility χ(T) of the heavy-electron superconductor UBe13 was investigated over temperatures ranging from 1.5 to 300 K and at pressures from 1 bar to 8 kbar. It is linear in pressure over the full temperature range, having a small constant pressure dependence at higher temperatures that increases rapidly below about T=150 K. The maximal value of the relative susceptibility change [1/χ(dχ/dP)] is about 1% per kbar. The Curie-Weiss law is obeyed in the temperature range 100 to 300 K with the effective magnetic moment peff=3.46μB independent of pressure, while the paramagnetic Curie temperature FTHETA∼-100 K becomes more negative with pressure. The lattice parameter of cubic UBe13 was measured as a function of pressure, permitting a determination of a compressibility value of -9.2×10-4 kbar-1 near ambient pressure. The pressure dependence of χ(T) is significantly weaker than that of the specific-heat coefficient C(T)/T; we discuss whether this can be resolved by (i) consideration of intersite antiferromagnetic interactions, or (ii) the quadrupolar Kondo-effect model, and conclude that the latter provides a stronger explanation of the results. © 1993 The American Physical Society.

The electrical resistivity of the heavy-electron superconductor UBe13 was investigated over temperatures ranging from 1 to 300 K and at high pressures from 12 to 152 kbar. The temperature, Tmax, at which attains a maximum increases linearly with pressure at two limiting rates: 0.25 K/kbar below 30 kbar and 0.65 K/kbar above 30 kbar. At low temperatures, the -versus-T data can be described by the expression =0+AT2 over a temperature interval of 1 K at 12 kbar to more than 16 K at 152 kbar. The coefficient A can be related to the Fermi-liquid energy scale T* by A-1/2 T*. The pressure dependence of A-1/2 also increases linearly with pressure at two limiting rates, with a crossover at about 50 kbar. The similarity in the pressure dependences of Tmax and A-1/2 suggests that both parameters are proportional to a single energy scale, while the changes in pressure dependence of Tmax and A-1/2 may represent a crossover from heavy-fermion to intermediate-valence behavior. © 1990 The American Physical Society.

The electrical resistivity of the heavy-electron superconductor UBe13 was investigated over temperatures ranging from 1 to 300 K and at high pressures from 12 to 152 kbar. The temperature, Tmax, at which attains a maximum increases linearly with pressure at two limiting rates: 0.25 K/kbar below 30 kbar and 0.65 K/kbar above 30 kbar. At low temperatures, the -versus-T data can be described by the expression =0+AT2 over a temperature interval of 1 K at 12 kbar to more than 16 K at 152 kbar. The coefficient A can be related to the Fermi-liquid energy scale T* by A-1/2 T*. The pressure dependence of A-1/2 also increases linearly with pressure at two limiting rates, with a crossover at about 50 kbar. The similarity in the pressure dependences of Tmax and A-1/2 suggests that both parameters are proportional to a single energy scale, while the changes in pressure dependence of Tmax and A-1/2 may represent a crossover from heavy-fermion to intermediate-valence behavior. © 1990 The American Physical Society.

Specific-heat and dc magnetic-susceptibility measurements have been performed on RBa2Cu3Ox (R denotes rare earth) compounds. These measurements show that the rare-earth atoms behave as local moments above the superconducting transition temperature of these compounds which can be as high or higher than in nonmagnetic YBa2Cu3Ox. Further, we find coexistence of superconductivity and magnetism in R=Gd,Er,andDy compounds and evidence for crystalline-electric-field splittings in these materials. © 1987 The American Physical Society.

We report the first Knight-shift studies of the heavy-fermion superconducting state. In 5 kOe the Knight shift of muons in superconducting U1-xThxBe13 remains near the normal-state value for x=0.033, but shows an unexpected strong decrease for x=0. If the pairing is of odd parity, this decrease suggests that the anisotropic order parameter is pinned to the lattice. The qualitatively different behavior for x=0.033 reflects either spin-orbit scattering by Th doping or a change of pairing symmetry. © 1986 The American Physical Society.

The electrical resistivity of the heavy-electron superconductor UBe13 has been measured at temperatures T between 0.1 and 300 K for pressures P to 16 kbar and in magnetic fields H up to 9 T. The temperature Tmax at which shows a maximum increases linearly with P at H=0 and with H2 for P=14.8 kbar. The resistivity, when normalized to its value at Tmax(P), scales as a function of reduced temperature T/Tmax(P) from 1 K to 1/41.4Tmax. At P=14.8 kbar, the magnetoresistance -[R(H)-R(0)]/R(0) behaves as a universal function of H/T for 1T6 K and 0

We have determined the effect of hydrostatic pressure on the susceptibility, on the T2 temperature dependence of the spin-fluctuation resistivity, and on superconductivity in UPt3. The spin-fluctuation temperature Ts, derived from the slope of resistivity versus T2, is used within a Fermi-liquid picture to calculate the susceptibility at T=0 K. The depression of this calculated with pressure agrees with the directly measured value lnP=-24 Mbar-1. Both the superconducting transition temperature Tc and the initial slope of the upper critical field also decrease under pressure. We find that lnTc/P=-25 Mbar-1 and speculate upon correlations between and Tc. © 1985 The American Physical Society.

Heavy-electron metals exhibit highly correlated electronic behavior at liquid helium temperatures, with conduction-electron masses some hundred times the free-electron mass. Whether "normal," antiferromagnetic, or superconducting, their electronic behavior differs drastically from their ordinary metallic counterparts. The physical origin of the large mass and unusual superconducting and magnetic properties is the strong coupling between the conduction electrons and the local f-electron moment fluctuations characteristic of these materials.

Fluid capacity measurements on the heavy formion superconductor UPt3 in an 11T magnetic field show that aboveapproximately 7 K, UPt3 behaves like the spin fluctuation compounds UAl2 and TiB2. Magnetoresistance measurements on UPt3 at 1.2 K also yield results similar to UAl2 in contrast to the other heavy fermion superconductors CeCu3Si3 and UBe1, which show a magneticresistance effect of opposite sign. Thus, experimental results permit continued speculation of triplet superconductivity in UPt3. © 1984 Elsevier Science Publishers B.V.

In contrast to the other magnetic Rare Earth (RE) ions for which the cubic Laves REIr2 compound is ferromagnetic, YbIr2 and TmIr2 are antiferromagnetic below 0.40 and 0.05 K, respectively. Both are trivalent above 4 K, with a possible reduced moment for TmIr2 below 0.3 K. In addition, CeIr2 and LuIr2 are superconductive below 0.20 and 0.23 K, respectively. © 1985.

Gadolinium impurities in UBe13 depress the Tc at an initial rate of -0.40 K/%, while in Th0.029U0.971Be13 the initial rate is only -0.19 K/%. This strongly suggests two different superconducting states. Further data on thorium depressions and critical fields are presented. © 1987.

We have investigated the effects of impurities on the heavy fermion system U2Zn17. The Neél temperature of 9.7 K in pure U2Zn17 is strongly depressed to below 1.5 K with 2% Cu (on the Zn site) or 20% Th (on the U site). The electronic specific heat coefficient is practically independent of impurity concentration above any magnetic ordering temperature. © 1986.

We have measured the electrical resistivity, thermoelectric power, magnetic susceptibility, Hall coefficient and upper critical field near Tc in EuBa2Cu3Ox, where 6.09

We have investigated the effects of pressure on the magnetoresistance and the upper critical magnetic field of the heavy electron compound UBe13. Both the superconducting transition temperature and the upper critical field decrease under hydrostatic pressure. The low temperature magnetoresistance remains large and negative under pressure. The temperature region over which the resistivity has a T2 temperature dependence increases with both magnetic field and with pressure. At a fixed magnetic field, the coefficient of the T2 term in the resistivity decreases strongly with pressure. UBe13 is found to have a pressure independent intrinsic residual resistivity of 18 μΦcm. © 1987.

We have measured the magnetic moment of (La0.9Ba0.1)2CuO4- as a function of temperature and magnetic field and have found the onset of superconductivity at a temperature T {reversed tilde equals} 35 K. From the magnetic field dependencies, we have shown that the sample is a type-II superconductor with ≲ {reversed tilde equals} 11. Specific heat measurements yield a finite electronic specific heat coefficient of ∼6 mJ/mole-K2 at 4 K and a Debye temperature of only 330 K, suggesting that a strong electron-phonon interaction may be responsible for the high T in our sample. © 1987.

Resistivity of (Th, U)Be13 under pressure may show the restoration of the onset of electron coherence. Unseparated rare earth elements can be used for preparation of high-Tc superconductors. © 1987.

The longitudinal and transverse upper critical magnetic fields Hc2 and Hc2 as a function of temperature T of a single-crystal specimen of the heavy-fermion superconductor UPt3 were measured resistively with the current flowing along the hexagonal c axis. The slope of the linear part of the Hc2 (T) curve near the superconducting transition temperature Tc=0.52 K equals 63 kOe/K, from which a zero-temperature superconducting coherence length 3/401/4120 can be inferred. An analysis using previously reported specific-heat data yields an effective mass ~200 times the free-electron mass and a value of 3/401/4170. The electrical resistivity between Tc and 8 K varies as Tn with n=1.6±0.1. © 1984 The American Physical Society.

To gain into the formation of the heavy Fermion state in CeCu2Si2 we have studied the relationship between the high temperature and low temperature physical properties. The single crystals are grown from metallic solvents, such as Sn, In or Ga. The low temperature susceptibility χ can be varied by factors of 5, and samples with smallest χ have the largest linear contribution γ to the specific heat. This "anticorrelation" of χ and γ is unexpected. The reduction of χ at low T is mainly due to a temperature independent antiferromagnetic molecular-field type interaction χ-1(T)=χ-10(T)+λ, and not due to interactions which become dominant below a characteristic temperature. Superconductivity occurs in small χ - large γ samples. © 1985.

We report the discovery of a new phase diagram in the magnetic field-temperature plane for single crystals of La2CuO4 that show no sign of antiferromagnetic order. The phase boundary is defined by magneto-resistance and susceptibility measurements. We discuss several possibilities that may lead to the phase diagram observed. © 1988.

We report μ+ zero-field relaxation and Knight shift studies of the heavy-fermion superconductors U1-xThxBe13, x=0 and 0.033. The Knight shift in UBe13 shows a strong decrease as the temperature is reduced in the superconducting state, unlike U0.967Th0.033Be13 in which the shift remains at about the normal state value. If the superconducting state in UBe13 has odd-parity, the decrease of Kμ below Tc suggests that the order parameter is pinned to the lattice. Either spin-orbit scattering or the existence of two distinct superconducting states with different spin susceptibilities in the (U,Th)Be13 system would explain the differences observed in the Th-doped and pure UBe13 materials. The latter hypothesis would exclude conventional BCS superconductivity. No evidence for magnetic order is seen in the zero-field relaxation rate for either material down to 0.3 K. © 1986 J.C. Baltzer A.G., Scientific Publishing Company.

The effect of a few per cent of thorium replacing uranium in the heavy-fermion superconductor UBe13 is dramatic. The low-temperature properties are drastically altered and a second transition of a controversial nature occurs below the onset of superconductivity. Other non-magnetic impurities are seen from various preliminary measurements to yield promise of different results. Normally such impurity studies show only gradual changes in properties, which are useful for extracting superconducting parameters, but the large effects seen in this heavy-fermoin superconductor highlight its exotic nature. © 1985.

We report measurements of the superconducting and magnetic behavior of GdBa2Cu3Ox. Superconductivity occurs below Tc = 95 and 93 K, respectively, for these compounds with large Meissner effects observed. The Gd-based compound has an upper critical field slope -dHc2 dT greater than 1.2 T/K. Both compounds exhibit Curie-Weiss behavior above Tc with free-ion effective moments and small, negative temperature intercepts. In addition, the Gd-based compound orders antiferromagnetically below 2.24 K with an entropy consistent with the ordering of seven unpaired spins. © 1987.

Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects on the superconducting and normal state properties. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression.

Magnetic fields as small as 4 kOe substantially increase the resistivity of U1-xThxBe13 for x=0.0175 and 0.0378 between 1.4 K and Tc, the superconducting transition temperature of this heavy fermion material. At the intermediate value of x=0.026, Tc reaches a local maximum, and no normal-state field dependence is observed up to 4 kOe. At x=0.0603, away from the region of nonmonotonic dependence of T c on x, again no field dependence is seen. The observations are discussed with regard to specific-heat measurements and in terms of the interaction of superconductivity with narrowband features.

We have investigated the source of the anisotropic susceptibility of UZn8.5 by preparing single crystals of UxTh 1-xZn8.5 for small x. Preliminary indications are that anisotropic exchange, rather than crystal field effects, are responsible for the anisotropy, but possible impurity contributions to the (anisotropic) susceptibility of the ThZn8.5 do not permit a stronger statement. Further measurements for small x show that both the electronic specific heat and the susceptibility at low temperature are strongly enhanced, and that Kondo-type resistivity minima are observed. The enhancements are somewhat reduced in the concentrated system UZn8.5.

We present electrical-resistivity, magnetic-susceptibility, specific-heat, and thermal-expansion data for UCd11. The low-temperature specific heat indicates that the electronic subsystem has a highly enhanced specific heat which is partially removed by a phase transition at 5.0 K. © 1984 The American Physical Society.

We report magnetoresistance measurements of the heavy electron compound UBe13 above the superconducting transition temperature Tc and below 4 K for pressures P up to 19 kbar and for magnetic fields H up to 9 T. We observe strong negative magnetoresistance at all pressures and temperatures. The resistivity ρ is quadratic in temperature T from Tc up to a maximum temperature of 1 K at 1 bar increasing to 2 K at 19 kbar. The slope of the T2 term decreases with both H and with P. We find that δ(H)≡-[ρ(H)-ρ(0)]/ρ(0) for a given pressure scales as a function of H/T and exhibits power-law behavior over one decade with an exponent of 1.7. In addition, δ(H) at high pressure shows this same power law over a more limited H/T range.

Convincing evidence has been discovered for bulk superconductivity in UPt3 at 0.54 K based on specific-heat, resistance, and ac susceptibility measurements. In addition, new evidence is presented that indicates that UPt3 is a spin-fluctuation system. If true, this is the first coexistent superconductor spin-fluctuation system. © 1984 The American Physical Society.

We report the first thorough characterization of single crystals of CeCu2Si2. Measurements on these flux-grown crystals, which are not superconducting above 0.050 K, include ac susceptibility, resistivity, Hall effect, and specific heat. A review of other measurements is given, and the implications of our single-crystal data are discussed. Specifically, our data are consistent with superconductivity in CeCu2Si2 being destroyed by having too low a Kondo temperature, although TKondo is not found to be inversely proportional to as previously claimed. The entropy associated with the low-temperature specific-heat anomaly is found to be only 0.66R ln2, in contrast to the previous result of R ln2 for polycrystalline material. The lack of superconductivity in our single crystals does not appear to be due to poor stoichiometry to +5%, as proposed previously for single crystals grown by a Bridgman technique. The possibility of charge-density waves suppressing superconductivity in strain-free material is discussed, although no experimental verification is found. © 1983 The American Physical Society.

We have prepared single crystals of NpBe13, Np0.68U0.32Be13, and PuBe13 and measured their resistivity, susceptibility, and specific heat down to low temperatures. NpBe13 has an itinerant-electron magnetic transition at 3.4 K, with a large temperature-dependent specific heat above this transition that is quite similar to that observed in the heavy-fermion superconductor UBe13 and a (T=0) of approximately 900 mJ/mole K2. PuBe13 may be described as a Kondo-type system, with certain inconsistencies. The data are compared to results for UBe13 and are consistent with a narrow f band at the Fermi energy in UBe13 moving lower in energy with the addition of f electrons in heavier actinide elements to create a Kondo resonance by PuBe13. © 1984 The American Physical Society.

Heavy-electron metals exhibit highly correlated electronic behavior at liquid helium temperatures, with conduction-electron masses some hundred times the free-electron mass. Whether "normal," antiferromagnetic, or superconducting, their electronic behavior differs drastically from their ordinary metallic counterparts. The physical origin of the large mass and unusual superconducting and magnetic properties is the strong coupling between the conduction electrons and the local f-electron moment fluctuations characteristic of these materials.

Specific-heat and dc magnetic-susceptibility measurements have been performed on RBa2Cu3Ox (R denotes rare earth) compounds. These measurements show that the rare-earth atoms behave as local moments above the superconducting transition temperature of these compounds which can be as high or higher than in nonmagnetic YBa2Cu3Ox. Further, we find coexistence of superconductivity and magnetism in R=Gd,Er,andDy compounds and evidence for crystalline-electric-field splittings in these materials. © 1987 The American Physical Society.

We have determined the effect of hydrostatic pressure on the susceptibility, on the T2 temperature dependence of the spin-fluctuation resistivity, and on superconductivity in UPt3. The spin-fluctuation temperature Ts, derived from the slope of resistivity versus T2, is used within a Fermi-liquid picture to calculate the susceptibility at T=0 K. The depression of this calculated with pressure agrees with the directly measured value lnP=-24 Mbar-1. Both the superconducting transition temperature Tc and the initial slope of the upper critical field also decrease under pressure. We find that lnTc/P=-25 Mbar-1 and speculate upon correlations between and Tc. © 1985 The American Physical Society.

The electrical resistivity of the heavy-electron superconductor UBe13 has been measured at temperatures T between 0.1 and 300 K for pressures P to 16 kbar and in magnetic fields H up to 9 T. The temperature Tmax at which shows a maximum increases linearly with P at H=0 and with H2 for P=14.8 kbar. The resistivity, when normalized to its value at Tmax(P), scales as a function of reduced temperature T/Tmax(P) from 1 K to 1/41.4Tmax. At P=14.8 kbar, the magnetoresistance -[R(H)-R(0)]/R(0) behaves as a universal function of H/T for 1T6 K and 0

Fluid capacity measurements on the heavy formion superconductor UPt3 in an 11T magnetic field show that aboveapproximately 7 K, UPt3 behaves like the spin fluctuation compounds UAl2 and TiB2. Magnetoresistance measurements on UPt3 at 1.2 K also yield results similar to UAl2 in contrast to the other heavy fermion superconductors CeCu3Si3 and UBe1, which show a magneticresistance effect of opposite sign. Thus, experimental results permit continued speculation of triplet superconductivity in UPt3. © 1984 Elsevier Science Publishers B.V.

We report the first Knight-shift studies of the heavy-fermion superconducting state. In 5 kOe the Knight shift of muons in superconducting U1-xThxBe13 remains near the normal-state value for x=0.033, but shows an unexpected strong decrease for x=0. If the pairing is of odd parity, this decrease suggests that the anisotropic order parameter is pinned to the lattice. The qualitatively different behavior for x=0.033 reflects either spin-orbit scattering by Th doping or a change of pairing symmetry. © 1986 The American Physical Society.

In contrast to the other magnetic Rare Earth (RE) ions for which the cubic Laves REIr2 compound is ferromagnetic, YbIr2 and TmIr2 are antiferromagnetic below 0.40 and 0.05 K, respectively. Both are trivalent above 4 K, with a possible reduced moment for TmIr2 below 0.3 K. In addition, CeIr2 and LuIr2 are superconductive below 0.20 and 0.23 K, respectively. © 1985.

Actinide compounds exhibit most of the known magnetic phenomena. Their properties are easily modified in intermetallic compounds. We present some new results on uranium ferromagnets and heavy fermion antiferromagnets and explain their implications. We show magnetic ordering in a high Tc superconductor. © 1987.

Small amounts of Sc, Lu, Gd, Np, Ce, Th, La, and Ba have been substituted for uranium in UBe13 to observe their effects on the superconducting and normal state properties. The thorium, which was the most complete study, resulted in an extremely unusual nonmonotonic depression of the transition temperature for a nonmagnetic impurity. This comes from an interplay that exists between the lowest temperature resistivity peak and the transition temperature, as the peak is depressed. These results suggest that heavy Fermion superconductivity is only one of the possible ground states for heavy mass electron systems. All of the impurities tested resulted in a transition temperature depression.

We have investigated the effects of impurities on the heavy fermion system U2Zn17. The Neél temperature of 9.7 K in pure U2Zn17 is strongly depressed to below 1.5 K with 2% Cu (on the Zn site) or 20% Th (on the U site). The electronic specific heat coefficient is practically independent of impurity concentration above any magnetic ordering temperature. © 1986.

Results of measurements of the electrical resistivity ρ{variant} between 0.04 and 1 K and the specific heat cp between 0.06 and 1 K of annealed polycrystalline CeCu6 are reported. ρ{variant} varies proportional to T2 below 0.1 K but is linear in T above 0.6 K. The specific heat is proportional to T below 0.5 K and the electronic specific-heat parameter γ = 1.53 J mole K2. © 1985.

We present electrical-resistivity, magnetic-susceptibility, specific-heat, and thermal-expansion data for UCd11. The low-temperature specific heat indicates that the electronic subsystem has a highly enhanced specific heat which is partially removed by a phase transition at 5.0 K. © 1984 The American Physical Society.

We have measured the electrical resistivity, thermoelectric power, magnetic susceptibility, Hall coefficient and upper critical field near Tc in EuBa2Cu3Ox, where 6.09