H. E. Schone

Magnetic shielding by Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / thick films

The magnetic shielding properties of YBCO thick-film shielding structures have been calculated using the Bean model, and these numerical results are compared to measured data. The numerical results were obtained with a three-dimensional finite-element code that performed a nonlinear, transient analysis of the superconducting material as a function of applied magnetic field. The superconducting properties of the Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) are included in this model by defining a nonlinear response of the high-temperature superconductor material to the applied field. The measurements were performed on superconducting, melt textured thick YBCO films deposited on cylindrical and planar substrates, which together formed a closed shielding structure. The YBCO shields were measured at various temperatures from 12 K up to T/sub c/. At 50 K these shields were found to completely shield a centrally placed magnetic probe up to an external field of 5 G.<<ETX>>

Static magnetic ordering of CeCu2.1Si2 found by muon spin relaxation

Abstract Zero- and longitudinal-field muon spin relaxation measurements on a poly-crystal sample of a heavy-fermion superconductor CeCu2.1Si2 ( Tc = 0.7 K) have revealed an onset of static magnetic ordering below T ∼ 0.8 K. The line shapes of the observed spectra in zero field indicate a wide distribution of static random local fields at muon sites, suggesting that the ordering is either spin glass or incommensurate spin-density-wave state. The observed width of the random local field at T = 0.05 K corresponds to a small averaged static moment of the order of 0.1μB per formula unit.

Sites and diffusion for muons and hydrogen in titanium hydrides

Low temperature sites for muons implanted in TiHx have been found to be a mixture of interstitial and substitutional sites, with substitutional occupancy determined by the probability that a muon in an interstitial site will have a vacant nearest neighbor substitutional site. As with ZrHx, activation from the interstitial site is observed below 300 K. From the depolarization rate in the substitutional site, the muon likely displaces the neighboring H atoms by about 0.1 A. Diffusion for the substitutional muons occurs above room temperature with an activation of about 0.38 eV, which is less than the 0.505 eV for hydrogen vacancy motion observed by NMR. To explain this the muon transition rate to a vacancy must be less than that of hydrogen.

Muon spin relaxation in CeCu2Si2 and muon knight shift in various heavy-fermion systems

Positive muon spin precession has been observed in various heavy-fermion systems in the transverse external magnetic field. In the superconductor CeCu2.1Si2, the relaxation rate of muon spins increases rapidly with decreasing temperature below TC. This is interpreted as the results of the inhomogeneous fields due to the imperfect penetration of the external field into the type-II superconducting state. The magnetic-field penetration depth λ is derived from the observed muon spin relaxation rate. λ is about 1200 ∢ at T∼0.5TC, and the temperature dependence of λ is consistent with the relation expected for a BCS superconductor. We have also measured the muon Knight shift Kμ in the normal (or paramagnetic) state of various heavy-fermion systems. Kμ is large and negative (about −1000∼−3000 ppm at T=10 K) for CeCu2Si2, UPt3 and CeAl3, while more complicated signals are measured in CePb3 and CeB6. The negative muon Knight shift in the non-magnetic heavy-fermion systems is discussed in terms of the Kondo-coupling between the conduction- and f-electrons.

Superconductivity and magnetic ordering in YBa2(Cu1−x Fe x )3O7

Transverse-and zero-field μSR measurements have been made for YBa2(Cu1−xFex)3O7 withx=0.04, 0.08 and 0.12. The temperature range studied was from approximately 7.5 K to 100 K. The onset of magnetic ordering commences at about 7.5 K forx=0.04, 10 K forx=0.08 and 20 K forx=0.12. The Gaussian depolarization parameter, σ ofGx(t) = exp(−σ2t2/2), is depressed by a factor of about 0.6 forx=0.04, but for thex=0.08 sample σ is depressed by a factor of 10 and increasing suppression is seen as the temperature is lowered below 45 K. This decrease in σ is interpreted in terms of decreasing electronic mean free paths.

Magnetic ordering in Nd2-xCexCuO4-y

The n-type cuprate superconductor and closely related samples of the general form Nd2−xCexCuO4−y have been studied with the muon spin relaxation technique. Non-super-conducting samples display antiferromagnetism (AFM) withTN below 150 K, the value being dependent upon both Ce concentration and oxygen depletion. The results are interpreted in terms of carrier concentration.

The superconducting properties of YBa2(Cu1−xMx)3O7 for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa2(Cu1−xNix)3O7−y withx=0.1 and 0.2, and YBa2(Cu1−xZnx)3O7−y withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs−1.1.6μs−1, and 1 μs−1 forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs−1, 0.75 μs−1, 0.65 μs−1, and 0.4 μs−1 forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.