Carlos Fainstein

Centro Atómico Bariloche · Solid State Group

We report here normal and superconducting properties of ABa2Cu3O7−δ (with A=Y, Gd, Dy, and Er) and of Fe doped YBa2Cu3O7−δ. Results from X-ray powder diffraction, electrical resistivity, magnetic susceptibility, ESR, and specific heat measurements are presented, leading to a characterization of the magnetic properties of these materials. The effect...

Spin-lattice Hamiltonian parameters have been derived from measurements of the effects of uniaxial stress upon the EPR of BaF2:Tm2+. Using these parameters, one may calculate spin-lattice relaxation rates for the direct process which are in excellent agreement with the measurements of Sabisky and Anderson. ENDOR has been used to measure the change...

The nuclear magnetic moment (uncorrected for diamagnetic shielding) and hyperfine structure parameters of 155Gd3+ in ThO2 have been obtained from ENDOR measurements performed at 35 GHz. The complete angular dependence of the ENDOR spectra can be explained by including a fourth-rank mixed tensor operator of second order in electronic and nuclear spi...

We report Alanine Dosimeter preparation, procedures for using the ESR/Dosimetry method, and the resulting calibration curve for gamma-irradiation in the range from 10-30 Gy. We use calibration curve to measure the irradiation dose in gamma-irradiation of human blood, as required in Blood Transfusion Therapy. The ESR/Alanine results are compared aga...

A comparative study by means of resonant Raman scattering and optical transmission spectroscopy between the different color centers originating from Fe(III) and Cu(II) doping of L-alanine crystals is presented. In both samples we find a selective resonant enhancement of Raman active modes related to vibrations of the lattice and carboxyl group. We...

We present a study of low concentration Fe(III) doping in crystalline L-alanine by means of electron paramagnetic resonance, resonant Raman scattering, and photoluminescence. The magnetic resonance experiments show that Fe(III) occupies two inequivalent sites of rhombic symmetry in the L-alanine crystal. We obtain for the principal directions of th...

The color centers in electron irradiated L-alanine crystals are studied by means of resonant Raman scattering and photoluminescence. We find a selective resonant enhancement of some of the Raman-active vibrations. The Raman resonant modes are either localized at the methyl group or belong to lattice modes comprising displacements of the ammonium gr...

We report transmission spectra of crystallites, taken from single crystal specimens of two plane Bi2Sr2Ca1(Cu1−x,Znx)2O8+δ, 0.0≤x≤0.05, diluted in CsI or polyethylene matrices In addition to weaker features assigned to unscreened phonons and a continuous background probably due to carriers, we found that the ratios of room temperature spectra to th...

We report transmission spectra of crystallites, taken from single crystal specimens of two plane Bi2Sr2Ca1(Cu1-x,Znx)2O8+delta, 0.0

We report measurements on x-rays diffraction and Raman, infrared and Mössbauer absorption spectra of Bi2Sr2Ca1(Cu1−x, Fex)2O8+δ, 0·05≤x≤0·25. X-ray analysis shows that the increment of Fe in the CuO2 layers results in the growing of the n=1 phase at the expense of the n=2, with possible segregation of Fe at the higher dopant concentration. Mössbaue...

XRD analysis and Mssbauer Spectroscopy studies were performed on samples of the ceramic oxide of nominal composition Bi2Sr2CaCu2O8 doped with iron substituting copper up to 25%. XRD results point out that increased doping favors the growth of the n=1 phase relative to the n=2 phase. RT Mssbauer spectra were fitted with three doublets D1, D2, and D3...

Mössbauer spectroscopy spectra of the ceramic Bi2Sr2Ca(Cu1-x Fe x )2O8+y forx=0, 0.005, 0.02 and 0.05 shows two doublets, that can be assigned to two different environments for the substituting ion. One of the sites is identified as a single Fe ion replacing a Cu ion in the CuO plane. The other site is associated with the dopant in an interstitial...

We measure the internal friction Q−1 in YBa2Cu3O7−x and Bi2Sr2CaCu2O8+x samples. At temperatures near 35K for KHz frequencies we observe an attenuation peak. In the case of YBa2Cu3O7−x, assuming a thermally activated relaxation behaviour, we are able to show that it corresponds to the same process as other peaks observed at higher frequencies. For...

Samples of Bi2Sr2Ca1Cu2O8+y doped with concentrations up to 5% iron were prepared and characterized by XRD, microprobe analysis, and electrical conductivity measurements. Mössbauer spectra on those samples show two doublets, one of which is concentration dependent. Analysis of the data allows for the assignment of the doublets to specific environme...

The response of the vortex structure in ceramic samples of Bi4Ca2Sr4Cu4O16+y has been measured by means of a vibrating reed technique in magnetic fields below 0.2 T. An anomally in the response of the reed is seen at temperatures of around 30 to 40 K, well below the critical temperature, indicating a transition similar to that attributed to a melti...

A sharp temperature and field dependent transition from a logarithmic to a non-logarithmic flux creep behavior has been found in BiSrCaCuO superconductors. The transition is not followed by any noticeable change in the magnetization. However, vibrating reed measurements show that it coincides with a strong hardening of the magnetic structure. The t...

A sharp temperature- and field-dependent transition from a logarithmic to a nonlogarithmic flux-creep behavior has been found in Bi-Sr-Ca-Cu-O superconductors. The transition is not followed by any noticeable change in the magnetization. However, vibrating-reed measurements show that it coincides with a strong hardening of the magnetic structure. T...

We have measured the thermal conductivity κ from 2 to 200 K in the superconducting ceramic EuBa2Cu3O7-x observing an anomaly at the superconducting transition temperature Tc. Using general arguments and approximations, and supposing that the electrical resistivity is due to electron-phonon interaction, we separate quantitatively the different contr...

Electron spin resonance on Gd3+ ions in GdxEu1-xBa2Cu3O7-δ are presented. The dependence of the g-factor and linewidth with the concentration of magnetic ions and temperature is discussed for superconducting and non superconducting samples with δ = 0 and δ = 0.7 respectively.

We report here experimental data on the crystal-field interaction of Gadolinium ions with their environment in GdxEu1-xBa2Cu3O7-delta. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples (x

We report here experimental data on the crystal-field interaction of gadolinium ions with their environment in GdxEu1−xBa2Cu3O7−δ. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples (x≪1) indicate the existence of a crystal-field splitting of the S728 ground state of Gd3+ ions of about 1.5 K. We discuss the parametrizati...

We have measured the specific heat of GdxEu1-xBa2Cu3O7-delta (0

We report normal and superconducting properties of Fe‐doped YBa 2 Cu 3 O 7-δ . Results from x‐ray powder diffraction, electrical resistivity, magnetic susceptibility, and ESR measurements are presented. The structural effects of doping are described and their correlation with the change in superconducting properties is discussed. Similarities with...

We have measured the thermal conductivity, Young modulus sound velocity and internal friction of a polycrystalline sample of the ceramic superconductor EuBa2Cu3O7-x. The low temperature data can be quantitavely understood assuming the interaction of phonons with tunneling systems.

We have studied the Mössbauer spectra of YBa2(Cu1−xFex)3O7+δ for several Fe concentrations (0.0018 ⩽ x ⩽ 0.10). We describe the experimental data with three doublets, A, B, and C, showing quadrupole splittings of 1.91(6), 1.10(6), and 0.55(6)mm/s, and isomer shifts of −0.07(2), −0.09(6), and 0.03(3)mm/s, respectively. At low concentrations doublet...

Internal friction Q-1 and Young Modulus sound velocity vE measurements at 1 kHz in YBa2Cu3O7−x and EuBa2Cu3O7−x polycrystalline samples reveal anomalies at the superconducting transition and at ∼37 K. The anomaly in vE at ∼90 K is accompanied by an absorption peak and is in agreement with published ultrasonic measurements, suggesting a lattice defo...

We have measured the internal friction Q-1 and the Young's-modulus sound velocity vE at 1 kHz for YBa2Cu3O7-x. Below 20 K the relative change in the sound velocity and the temperature dependence of the internal friction perfectly resemble the behavior obtained for Suprasil W. Below 1 K we observe a logarithmic temperature dependence for the sound v...

Electron spin resonance on Gd3+ ions in GdxEu1-xBa2Cu3O7-δ are presented. The dependence of the g-factor and linewidth with the concentration of magnetic ions and temperature is discussed for superconducting and non superconducting samples with δ = 0 and δ = 0.7 respectively.

Results of electron-nuclear double-resonance experiments performed on four shells of fluorine nuclei surrounding Yb3+ impurities at cubic sites in the four fluorite lattices CdF2, CaF2, SrF2, and BaF2 are reported. The data are described in terms of a Hamiltonian for the transferred hyperfine interactions (THFI) including an anisotropic nuclear Zee...

We have measured the dc magnetization, electron spin resonance (ESR) linewidth and ESR line shift δH r for the spin‐glass Ag‐Mn x (x=4 and 8 at. %) as a function of adding magnetic impurities (Er and Gd). We determine the anisotropy constant from the relation K=δH r M⁰, where M⁰ is the magnetization measured at the dc field co...

We have calculated the lattice distortions around trivalent rare-earth dilute impurities, occupying substitutionally metal sites in fluorites. Explicit results are given for the equilibrium positions of the nearest fluorine ligands, R, the induced electric dipole moments, and the local hydrostatic strains for MF2 (M=Cd, Ca, Sr, Pb, and Ba). These r...

We have measured the effect of uniaxial stress on the fluorine-transferred hyperfine interaction for Tm2+:CaF2 and Tm2+:SrF2 using electron-nuclear double-resonance (ENDOR) techniques. We obtain for ∂(As-Ap)/∂P the values 4.3(4) kHz kg-1 mm2 and 4.2(3) kHz kg-1 mm2, respectively. These results, as well as those obtained for the same hosts without a...

Microwave spectroscopy is used to study gadolinium orthovanadate in the antiferromagnetic phase, from 2.2 to 1.4 K. AFMR data at 9.4 and 34.8 GHz are analyzed and the temperature dependence for the anisotropy constant is obtained.On a etudié gadolinium Orthovanadate dans la phase antiferromagnétique par spectroscopie de microonde entre 2,2 et 1,4 K...

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We report experimental data on the crystal field interaction of Gd ions with their environment in Gd/sub x/Eu/1-x/BaâCuâOâ. The ESR spectrum and a Schotiky anomaly in the specific heat of dilute samples indicate the existence of a crystal field splitting of the ⁸Sââ ground state of the Gd/sup 3 +/ ions of about 1.5K. Since the single ion energies...

We have measured the internal friction Q⁻¹ and the Young's-modulus sound velocity v/sub E/ at 1 kHz for YBaâCuâOââ/sub x/. Below 20 K the relatiave change in the sound velocity and the temperature dependence of the internal friction perfectly resemble the behavior obtained for Suprasil W. Below 1 K we observe a logarithmic temperature dependence...

We have measured the thermal conductivity kappa from 2 to 200 K in superconducting ceramic EuBaâCuâOââ/sub x/ observing an anomaly at the superconducting transition temperature T/sub c/. Using general arguments and approximations, and supposing that the electrical resistivity is due to electron-phonon interaction, we separate quantitatively the dif...

We report here experimental data on the crystal-field interaction of Gadolinium ions with their environment in Gd/sub x/Eu/sub 1-x/BaâCuâOââ/sub delta/. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples (x

We report normal and superconducting properties of Fe-doped YBaâCuâOââ/sub delta/. Results from x-ray powder diffraction, electrical resistivity, magnetic susceptibility, and ESR measurements are presented. The structural effects of doping are described and their correlation with the change in superconducting properties is discussed. Similarities w...

We measured the angular dependence of the g-shifts of the Gamma7 doublet in Dy3+ : CaF2 under uniaxial stress. The data are compared with the predictions of a model for the orbit-lattice interaction.