151Eu Mössbauer and magnetic studies on magnetic superconductor EuSr2 Ru1 - x Cu2 + x O8 ( - 0.1 ≤ x ≤ 0.25 )

Magnetic and 151Eu Mössbauer studies have been carried out on the ruthenocuprate magnetic superconductors,EuSr2Ru1-xCu2+xO8(-0.1≤ x ≤0.25). The magnetic ordering temperature (TM) decreases from 135 K for x=0.0 to 125 K for x=0.25 and the superconducting transition temperature increases from 19 K (onset for x=0.0) to 33 K (x=0.1). The compounds with x<0 do not show superconductivity down to 2 K but show an increase in TM. The 151Eu Mössbauer studies show that the Eu ions are in 3+ (4f6,J=0) and hence in the nonmagnetic state in these compounds. The observation of a broadening in the 151Eu Mössbauer absorption spectra below the magnetic ordering temperature indicates a small transferred magnetic hyperfine field at the Eu site.© Elsevie

Investigation of magnetic interactions in Ba2EuRu1-xCuxO6 using magnetization and Eu-151 Mossbauer studies

We report here the magnetization and Eu-151 Mossbauer studies in ordered perovskite-type oxides, Ba2EuRu1-xCUxO6 (x=0.0, 0.1 and 0.2). The parent compound, Ba2EuRuO6, shows a magnetic ordering at 40 K. Both the magnetization and Mossbauer measurements indicate that the magnetic ordering temperature is unchanged as Cu partially substitutes Ru. Despite the fact that the ground state of Eu3+ is a nonmagnetic J=O state, the Eu-151 Mossbauer resonance spectrum shows a clear splitting into six lines for T < T-N, indicating a large magnetic hyperfine field (similar to 280 kOe). This large hyperfine field may be arising due to a strong exchange field between the ordered Ru moments acting on the Eu3+ ions, inducing a magnetic moment for the Eu3+ ions. (c) 2005 American Institute of Physics

Transport and magnetic properties of Nd1−xPbxMnO3Nd_{1- x}Pb_xMnO_3 single crystals

Transport and magnetic properties of flux-grown $Nd_{1-x}Pb_xMnO_3$ single crystals (x-0.15–0.5) are studied in the temperature range 300–77 K and 280–2 K, respectively. Magnetization measurements with a superconducting quantum interference device confirm a paramagnetic to ferromagnetic transition around 110, 121, 150, 160, and 178 K for x-0.15, 0.2, 0.3, 0.4, and 0.5, respectively. Four probe resistivity measurements at low temperatures show a monotonic increase for x-0.15 which represents a ferromagnetic insulating (FMI) phase. For $Nd_{0.8}Pb_{0.2}MnO_3$ there is a slope change present in the resistivity profile at 127 K where metal to insulator transition (MI) sets in. For x-0.3 this MI transition is more prominent. However, both these samples have FMI phase at low temperature. When the concentration of lead increases $(x>0.3)$ the sample displays a clear insulator to metal transition with a low temperature ferromagnetic metallic phase. On the basis of these measurements we have predicted the phase diagram of $Nd_{1-x}Pb_xMnO_3.$ Magnetization measurements by a vibration sample magnetometer point out the appreciable differences between zero field cooled and field cooled profiles below the ferromagnetic to paramagnetic transition temperature for all x. These are indicative of magnetic frustration

Magnetic, transport and 151Eu Mössbauer studies on partially doped La1 - x Eux Sr0.2 MnO3 ( 0.04 ≤ x ≤ 0.32) compounds

Electrical resistivity, magnetic susceptibility and 151Eu Mössbauer studies have been carried out on La1-xEuxSr0.2MnO3 (0.04≤ x 0.32) compounds. As Eu substitution for La increases, the Curie temperature (TC) decreases from 261 K for x=0.04 to 187 K for x=0.16 along with a decrease in the metal–insulator transition temperature. However, the x=0.32 sample shows an increase in TC to 224 K along with an increase in the metal–insulator transition. The 151Eu Mössbauer studies show that all the Eu are in 3+(4f6,J=0) nonmagnetic state. Broadening of the Mössbauer spectra below TC indicates a transferred magnetic hyperfine field at the Eu site.© Elsevie

Magnetization and heat capacity studies of double perovskite compounds Ba(2)SmRuO(6) and Ba(2)DyRuO(6)

Here we report the magnetic and heat capacity studies of the double perovskite compounds Ba(2)SmRuO(6) and Ba(2)DyRuO(6). Anti ferromagnetic transitions are inferred at 54 and 47 K in Ba(2)SmRuO(6) and Ba(2)DyRuO(6), respectively, in the magnetization measurements. Heat capacity measurements show large jumps at the corresponding temperatures and confirm the bulk magnetic ordering. Both the measurements provide clear indication of the ordering of the rare earth moments also along with the Ruthenium moments. However, the heat capacity results suggest that the ordering of rare earth magnetic moments is spread over a large temperature range. An anomaly observed in the magnetization measurements at 42 K (below the magnetic ordering) in Ba(2)SmRuO(6) is discerned as a reorientation of Sm(3+) moments. (C) 200

The second magnetization peak and the peak effect phenomenon in the superconductor Ca3Rh4Sn13

We report on the observation of the anomalous second magnetization peak (SMP) and the peak effect (PE) in juxtaposition to each other in the isothermal magnetization hysteresis loops at T ≤ 4 K in a weakly pinned single crystal of an isotropic superconductor Ca3Rh4Sn13 (Tc≈8.2 K). The position of the SMP does not display any temperature variation, whereas the PE appearing at the edge of the irreversibility line progressively moves towards lower fields as temperature increases. At T≈5 K, the PE nearly swamps the SMP, and above this temperature only the PE can be observed. If the SMP and the PE can be construed as representing changes in the spatial order of the flux line lattice (FLL), the apparent merger of loci of the peak fields of the SMP and the PE in the neighborhood of H≈15 kOe at a reduced temperature t [=T/Tc(0)] of about 0.6 could imply the existence of a multi-critical point.© Elsevie

Magnetic, specific heat and 151Eu Mössbauer studies on Ba2EuRu1-xCuO6(0≤x≤0.2) compounds

Magnetic, 151Eu Mössbauer and specific heat measurements have been carried out on image compounds. From the magnetization data, all the compounds are found to be antiferromagnetically ordered near 40 K, independent of Cu content. A sharp peak at 40 K in the specific heat data also confirms the magnetic ordering. The Eu ions in all the compounds are in the 3+ state as inferred from the 151Eu Mössbauer isomer shift values. However, a well split, six line pattern is observed in the 151Eu Mössbauer spectra of these compounds below 40 K. This is rather rare for image which is a nonmagnetic ion. The magnetic hyperfine field at the Eu site is found to be image at 4.2 K and is presumed to arise due to the strong Ru–O–Eu exchange interaction.© Elsevie

Multiple magnetization peaks in weakly pinned Ca3Rh4Sn13 and YBa2Cu3O7-delta

The second magnetization peak and the peak effect anomaly coexisting in a given isothermal magnetization hysteresis loop show striking similarities in Ca3Rh4Sn13, a low-T-c superconductor and YBa2Cu3O7-delta, a high T-c superconductor. The observed variation of the hysteresis width with field could imply a modulation in the degree of the plastic deformation of the elastic vortex solid. The characteristics of the high-T-c cuprates, such as large Ginzburg number, short coherence length, decoupling of the Josephson coupled pancake vortices, etc., are unlikely to be the cause of the observed behavior

Glasslike ordering and spatial inhomogeneity of magnetic structure in Ba3FeRu2O9: Role of Fe/Ru site disorder

Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9, have been studied over a significant period of time to understand the unusual magnetism of ruthenium metal. However, among them, the M = Fe compound appears different since it is observed that unlike others, the 3d Fe ions and 4d Ru ions can easily exchange their crystallographic positions, and as a result many possible magnetic interactions become realizable. The present study involving several experimental methods on this compound establishes that the magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H ruthenates. Local structural study reveals that the possible Fe/Ru site disorder further extends to create local chemical inhomogeneity, affecting the high-temperature magnetism of this material. There is a gradual decrease of Fe-57 Mossbauer spectral intensity with decreasing temperature (below 100 K), which reveals that there is a large spread in the magnetic ordering temperatures, corresponding to many spatially inhomogeneous regions. However, finally at about 25 K, the whole compound is found to take up a global glasslike magnetic ordering