E. Zirngiebl

Superconductivity of rare earth-barium-copper oxides

Abstract We report the superconductivity of R-Ba-Cu-O compounds for rare earths R = Sm through Ho. The Nd and Tm compounds were not observed to be superconducting. The Tc onsets for the Eu and Gd compounds are comparable to that observed for Y-Ba-Cu-O. An approximate value for the upper critical field slope of the Gd compound is given.

Electron paramagnetic resonance, electrical resistivity, and magnetization studies in the high Tc superconductors EuBa2Cu3O9−xandEuBa2 (Cu1−yMy)3O9−x (M = Cr, Mn, Fe, Co, Ni, ORZn)☆

Abstract We have measured electron paramagnetic resonance (EPR), electrical resistivity, and dc magnetic susceptibility from 2 K – 300 K for the high T c oxide superconductor EuBa 2 Cu 3 O 9−x , either undoped or doped with 3d ions (Cr, Mn, Fe, Ni, Co, or Zn), which presumably substitute at the Cu sites. We have observed an EPR line at low temperatures (T ≤ 40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The EPR linewidth is also temperature dependent and exhibits a minimum at about 15 K. In some of the samples another EPR signal is observed over the entire temperature range studied, with properties that depend on sample preparation conditions. This signal is likely to be due to small amounts of an additional phase. The behavior and origin of these EPR signals are discussed. The variation of T c with 3d ion concentration over the range (1 – 8%) is also presented.

Magnetic and thermal measurements on high-Tc (La0.9Ba0.1)2CuO4-y

Abstract We have measured the magnetic moment of (La 0.9 Ba 0.1 ) 2 CuO 4- as a function of temperature and magnetic field and have found the onset of superconductivity at a temperature T ⋍ 35 K. From the magnetic field dependencies, we have shown that the sample is a type-II superconductor with ≲ ⋍ 11. Specific heat measurements yield a finite electronic specific heat coefficient of ∼6 mJ/mole-K 2 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.

Magnetic anisotropy in the UxTh1−xZn8.5 system

We have investigated the source of the anisotropic susceptibility of UZn8.5 by preparing single crystals of UxTh1–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.

EPR, magnetization, and resistivity studies in doped (4‐f or 3‐d ions) and undoped RBa2Cu3Oy high TC superconductors (R=Y,Pr,Nd,Eu,Gd,Ho,Er, or Yb) (abstract)

We have measured electron paramagnetic resonance (EPR), resistivity, and dc susceptibility from 2 to 300 K for the oxide high Tc superconductors (R)Ba2Cu3Oy (R=Y,Pr,Nd,Eu,Gd,Ho,Er,Tm, or Yb). Selected systems were doped with 3‐d ions (Cr,Mn,Fe,Ni,Co, or Zn) or 4‐f ions (Gd or Er) which presumably substitute for the Cu or R site, respectively. In the systems studied we have observed an EPR line at low temperatures (T<40 K), which exhibits an increase in intensity and decrease in field for resonance as the temperature is lowered. The ESR linewidth is also temperature dependent and exhibits a minimum at about 15 K. An additional EPR line that can be associated with a Gd3+, Mn2+ or Er3+ ion was observed for those samples where these ions were present as dilute impurities. In some of the samples another EPR signal is observed with properties that depend on sample preparation conditions. The behavior and origin of all lines will be discussed. The variation of Tc with concentration of the added impurities over t...

Low Temperature Properties of CeCu5 and Related Compounds

The reported phase diagram1 of the Ce-Cu system contains five compounds and a meta-stable sixth compound, CeCu3.6.2 CeCu6 is by far the most investigated compound, primarily because of its heavy Fermion behavior at low temperature.3 It is this feature which makes comparisons with other Ce-Cu compounds of special interest. Several studies have been reported on both CeCu2 5,6 and CeCu5.7,8 We present here our results on CeCu5, partly because they include properties not included in Refs. 7 and 8, and partly because our results differ in one important respect, namely in the observation of two distinct phase transitions at low temperature.

EPR, Magnetization, and Resistivity Studies in DOPED (4f, 3d Ions) and Undoped R (or Y) Ba2Cu3O9−x High Tc Superconductors

After years of searching for superconductors with higher transition temperatures, an incredible success has been achieved in recent months, as a consequence of the discovery of Bednorz and Muller of a 30 K transition in La2-yBayCuO4-x,1 followed by the subsequent findings that YBa2Cu2O9-x has a Tc well above liquid nitrogen temperatures.2,3 These discoveries have resulted in an explosive growth of interest in the field, with the present challenge being to explain the pertinent superconducting mechanisms.

Phonon Raman scattering in superconductingLa1.85Sr0.15CuO4−y

We have performed Raman scattering experiments on the high-T/sub c/ superconductor La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ (T/sub c/approx. =37 K). We observe three of the four Raman-active optical phonon modes and, on the basis of a comparison to the Raman spectra of K/sub 2/MnF/sub 4/, are able to tentatively assign the mode symmetries. No anomalous temperature dependence is observed for all three modes, indicative of the lack of strong electron-phonon coupling in these modes.

Phonon Raman scattering in superconducting La/sub 1. 85/Sr/sub 0. 15/CuO/sub 4-//sub y/

We have performed Raman scattering experiments on the high-T/sub c/ superconductor La/sub 1.85/Sr/sub 0.15/CuO/sub 4-//sub y/ (T/sub c/approx. =37 K). We observe three of the four Raman-active optical phonon modes and, on the basis of a comparison to the Raman spectra of K/sub 2/MnF/sub 4/, are able to tentatively assign the mode symmetries. No anomalous temperature dependence is observed for all three modes, indicative of the lack of strong electron-phonon coupling in these modes.

Normal State Magnetic Behavior of (U1−xREX)BE13 Pseudobinaries

To understand the underlying physics of the heavy electron superconductor UBe13,1 its superconducting transition temperature Tc and its critical field behavior have been studied extensively as a function of impurity doping.2−5 Thorium and yttrium substitution on uranium lattice sites generate a non-monotonic Tc suppression as a function of impurity concentration. Moreover, for Th-substitutions x, 0.02 < x < 0.04, a second large anomaly appears4 in the specific heat below Tc, perhaps indicating the transition to a second superconducting phase.6 Doping of UBe13 with magnetic Gd impurities results in an unusually small Tc suppression (ΔTC/Gd = −0.40 K/%). On the other hand, adding a few percent of nonmagnetic impurities (La, Sc, Lu) suppresses Tc rapidly, being an unusually strong effect of nonmagnetic impurities on superconductivity. Altogether, any impurity doping seems to modify the low temperature properties of UBe13 in a way rather unusual compared to normal superconductors. So far, however, little attention has been paid to the modification of the normal state properties of impurity doped UBe13. We have investigated the normal state magnetic behavior of impurity doped (U1−xREx)Be13 pseudobinaries (RE = Th, Y, La, Lu, Sc) in the temperature range between 2 K and 380 K for impurity concentrations x ≤ 0.05 to see if there are correlations with Tc(x).