Nonlinear magnetic response in ruthenocuprates

Abstract.: We have performed an investigation of the nonlinear magnetic response in ruthenocuprates. A negative, diverging-like peak at the main magnetic transition TN in RuSr2 RECu2O8 (RE = Gd, Y) indicates a possible canted antiferromagnetic order. Another well defined feature above TN points to a blocking of superparamagnetic particles through the T-3 dependence of the third harmonic at higher temperatures. Below TN a nondiverging peak appears, which is strongly affected by the addition of 10% of Cu ions in the RuO2 planes. In RuSr2 RE 2-xCexCu2O10 the main magnetic transition TM is accompanied by two characteristic temperatures in the third harmonic of the ac susceptibility, in agreement with recent studies from μSR and Mössbauer spectroscopy. We find that the spin-spin correlation temperature is the same in both families of ruthenocuprate

Nonlinear magnetic response in ruthenocuprates

We have performed an investigation of the nonlinear magnetic response in ruthenocuprates. A negative, diverging-like peak at the main magnetic transition T_N in RuSr2RECu2O8 (RE = Gd, Y) indicates a possible canted antiferromagnetic order. Another well defined feature above T_N points to a blocking of superparamagnetic particles through the T^(-3) dependence of the third harmonic at higher temperatures. Below T_N a nondiverging peak appears, which is strongly affected by the addition of 10% of Cu ions in the RuO2 planes. In RuSr2RE(2-x)Ce(x)Cu2O10 the main magnetic transition T_M is accompanied by two characteristic temperatures in the third harmonic of the ac susceptibility, in agreement with recent studies from uSR and Mossbauer spectroscopy. We find that the spin-spin correlation temperature is the same in both families of ruthenocuprates.Comment: accepted for publication in EPJ

Structural Order and Disorder in Co-Based Layered Cuprates CoSr2(Y,Ce)sCu2O5+2s (S=1-3)

Crystal structures of a homologous series of Co-Based layered cuprates, CoSr2(Y,Ce)sCu2O5+2s (s=1-3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. for all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO4- tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. for the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO2 planes, HREM and ED analysis revealed complete disorder of the CoO4 chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers. © 2003 Elsevier Inc. All rights reserved

Antiferromagnetism and Superconductivity: Cuprate Plane Magnetic Ordering in Y Sr2 Cu2.1 Nb0.9 O8-Δ

YSr2Cu2.1Nb0.9O8-δ, prepared using a high-pressure, high-temperature process, has been studied using superconducting quantum interference device magnetometry, neutron diffraction, and electron spin resonance (ESR). This material, in which Cu is the only magnetic ion, shows two magnetic transitions below room temperature, at 257 and 27 K. While neutron diffraction fails to find antiferromagnetic Bragg peaks, ESR unambiguously shows that the compound is antiferromagnetic. Antiferromagnetic resonance is observed for temperatures below to slightly above the lower ordering temperature. the magnetization data can be understood as arising from ferromagnetic Cu O2 planes, which are coupled as (independent) antiferromagnetic bilayers at the upper transition and then subsequently show full, three-dimensional order at the lower transition. This lightly hole-doped material shows a small diamagnetic response, closely coincident with the lower magnetic transition. the difference in field-cooled and zero-field-cooled magnetization curves is attributed to meta magnetism, arising from the weak coupling of the cuprate plane bilayers. the field-cooled magnetization data are strikingly similar to that reported for the so-called ferromagnetic superconductor GdSr2Cu2RuO8, for which the anomalous magnetization has been attributed to Ru moment canting. the absence of any magnetic ion other than Cu in this compound excludes that explanation. © 2007 the American Physical Society

Antiferromagnetism and Superconductivity: Magnetic Order in Y Sr2 Cu2.1 Ru0.9 O7.9

Superconducting (Tc ∼40 K) YSr2Cu2.1Ru0.9O7.9, prepared by a high-temperature high-pressure process, has been studied by electron spin resonance (ESR), neutron diffraction and superconducting quantum interference device magnetometry. Neutron diffraction confirms the antiferromagnetic ordering of the Ru atoms at TN-Ru ∼140 K, as reported by Lynn and Takagiwa ESR data show antiferromagnetic order that persists well above the Ru ordering temperature, with an intensity that peaks close to TN-Ru. the ESR data are very similar to those observed in GdSr2Cu2RuO8 and YSr2Cu2.1Nb0.9O7.9. the apparent ferromagnetism observed at TN-Ru cannot arise from the strongly coupled c -axis-ordered Ru moments, which exhibit no canting; rather it appears to be due to a metamagnetic response of the cuprate planes induced by the Ru order. Magnetization data show the system as consisting of more than one magnetically ordered species; the magnetization is nonlinear well above TN-Ru, indicating that Cu atoms are ordered above that temperature. the neutron diffraction data at 16 K show additional intensity on the (0,0,1) reflection. Although Takagiwa attribute this to ferromagnetism, the polarized neutron data of Lynn on GdSr2Cu2RuO8 rule out this explanation. These data, however, can be successfully modeled with ferromagnetic cuprate planes that are antiferromagnetically stacked. the refined Cu moment is found to be 0.4 (0.2) μB. the (0,0,1) magnetic Bragg peak is broadened relative to the nuclear peak, presumably due to a short correlation length of the magnetic domains along the c axis. the similarity of the magnetization curves in this compound and in YSr2Cu2.1Nb0.9O7.9 suggests that cuprate plane ordering is a common feature in this class of materials, which is very closely related to YBa2Cu3O7-δ. © 2007 the American Physical Society

Physical Property Characterization of Bulk MgB2 Superconductor

We report synthesis, structure/micro-structure, resistivity under magnetic field [R(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity K(T), and magnetization of ambient pressure argon annealed polycrystalline bulk samples of MgB2, processed under identical conditions. The compound crystallizes in hexagonal structure with space group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs showing various types of defect features along with the presence of 3-4nm thick amorphous layers forming the grain boundaries of otherwise crystalline MgB2. Raman spectra of the compound at room temperature exhibited characteristic phonon peak at 600 cm-1. Superconductivity is observed at 37.2K by magnetic susceptibility C(T), resistivity R(T), thermoelectric power S(T), and thermal conductivity K(T) measurements. The power law fitting of R(T) give rise to Debye temperature at 1400K which is found consistent with the theoretical fitting of S(T), exhibiting ThetaD of 1410K and carrier density of 3.81x 1028/m3. Thermal conductivity K(T) shows a jump at 38K, i.e., at Tc, which was missing in some earlier reports. Critical current density (Jc) of up to 105 A/cm2 in 1-2T (Tesla) fields at temperatures (T) of up to 10K is seen from magnetization measurements. The irreversibility field, defined as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe at 4, 10 and 20K respectively. The superconducting performance parameters viz. irreversibility field (Hirr) and critical current density Jc(H) of the studied MgB2 are improved profoundly with addition of nano-SiC and nano-Diamond. The physical property parameters measured for polycrystalline MgB2 are compared with earlier reports and a consolidated insight of various physical properties is presented.Comment: 41 pages TEXT+Fig

Physical property characterization of single step synthesized NdFeAsO0.80F0.20 bulk 50K superconductor

We report an easy single step synthesis route of title compound NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R=0) at 48 K and a very high upper critical field (Hc2) of up to 345 Tesla. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and thus ruling out the presence of any ordered FeOx impurity in the matrix. In specific heat measurements a jump is observed in the vicinity of superconducting transition (Tc) along with an upturn at below T=4 K due to the AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is negative down to Tc, thus indicating dominant carriers to be of n-type in NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain contributions have been individuated by looking at various amplitude and frequencies of the applied AC drive magnetic field.Comment: 26pages text + Figures: comments/suggestions welcome ([email protected] & http://www.freewebs.com/vpsawana

Physical property characterization of single step synthesized NdFeAsO

We report an easy single step synthesis route of title compound NdFeAsO0.80F0.20 superconductor having bulk superconductivity below 50 K. The title compound is synthesized via solid-state reaction route by encapsulation in an evacuated (10-3 Torr) quartz tube. Rietveld analysis of powder X-ray diffraction data shows that compound crystallized in tetragonal structure with space group P4/nmm. R(T)H measurements showed superconductivity with Tc (R = 0) at 48 K and a very high upper critical field (Hc2) of up to 345 T. Magnetic measurements exhibited bulk superconductivity in terms of diamagnetic onset below 50 K. The lower critical field (Hc1) is around 1000 Oe at 5 K. In normal state i.e., above 60 K, the compound exhibited purely paramagnetic behavior and thus ruling out the presence of any ordered FeOx impurity in the matrix. In specific heat measurements a jump is observed in the vicinity of superconducting transition (Tc) along with an upturn at below T = 4 K due to the AFM ordering of Nd+3 ions in the system. The Thermo-electric power (TEP) is negative down to Tc, thus indicating dominant carriers to be of n-type in NdFeAsO0.80F0.20 superconductor. The granularity of the bulk superconducting NdFeAsO0.8F0.2 sample is investigated and the intra and inter grain contributions have been individuated by looking at various amplitude and frequencies of the applied AC drive magnetic field

Structural and magnetic studies on PrBa2Fe3O8

It is known that Fe moments order antiferromagnetically with Néel temperature, TN, above 700 K in RBa2Fe3O7-δ with R=Y and Eu, and Pr moments order antiferromagnetically in PrBa2Cu3,O7-δ, with TN of 17 K. We have synthesized PrBa2Fe3O8 to study the ordering of Pr and Fe moments. From X-ray and neutron diffraction studies, this compound is found to crystallize in the tetragonal structure (space group P4/mmm). 57Fe Mössbauer studies show a complex hyperfine split pattern at 77 K, but a doublet superimposed on a six-line pattern at 300 K implying that some of the Fe moments order magnetically between 77 and 300 K while others may have ordering temperature of more than 300 K. Magnetization measurements reveal discontinuities in the susceptibility data around 80 and 20 K, probably an indication of magnetic ordering of the Fe and Pr moments. Neutron diffraction studies at 300 K suggest the presence of additional oxygen in the Pr plane and a magnetic structure very different from that of YBa2Fe3O8

Physical property characterization of bulk MgB

We report synthesis, structure/micro-structure, resistivity under magnetic field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity κ(T), and magnetization of ambient pressure argon annealed polycrystalline bulk samples of MgB2, processed under identical conditions. The compound crystallizes in hexagonal structure with space group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs showing various types of defect features along with the presence of 3–4 nm thick amorphous layers forming the grain boundaries of otherwise crystalline MgB2. Raman spectra of the compound at room temperature exhibited characteristic phonon peak at 600 cm-1. Superconductivity is observed at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) measurements. The power law fitting of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is found consistent with the theoretical fitting of S(T), exhibiting Θ D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was missing in some earlier reports. Critical current density (Jc) of up to 105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K is seen from magnetization measurements. The irreversibility field, defined as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe at 4, 10 and 20 K respectively. The superconducting performance parameters viz. irreversibility field (Hirr) and critical current density Jc(H) of the studied MgB2 are improved profoundly with addition of nano-SiC and nano-diamond. The physical property parameters measured for polycrystalline MgB2 are compared with earlier reports and a consolidated insight of various physical properties is presented