Magnetotransport of lanthanum doped RuSr2GdCu2O8 - the role of gadolinium

Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO2 planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K for low applied magnetic field and the gadolinium sublattice antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a complicated temperature dependence due to the combination of the two magnetic orderings and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO2 layers while the gadolinium magnetism influences the conductivity in the CuO2 layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic when gadolinium orders antiferromagnetically.Comment: 7 pages, 9 figures, submitted to European Physical Journal

Mikrovalna vodljivost tankih listova YBCO u magnetskom polju

The microwave response of a thin film of high temperature superconductor YBa2Cu3O7 - δ was measured for a wide region of temperatures and magnetic fields. From the measured complex frequency shift, the complex conductivity was calculated. The model for effective conductivity in the mixed state was fitted to the complex conductivity data and the values of upper critical fields Bc2(T) and depinning frequencies ω0 (T) have been obtained as fitted parameters.Mjerili smo mikrovalni odziv tankog filma visokotemperaturnog supravodiča YBa2Cu3O7−δ u širokom području temperatura i magnetskih polja. Iz izmjerenog kompleksnog frekventnog pomaka izračunali smo kompleksnu vodljivost. Numeričkom prilagodbom modela efektivne vodljivosti u miješanom stanju odredili smo vrijednosti gornjeg kritičnog polja Bc2 (T) i frekvencije opuštanja ω0(T)

Mikrovalna vodljivost tankih listova YBCO u magnetskom polju

The microwave response of a thin film of high temperature superconductor YBa2Cu3O7 - δ was measured for a wide region of temperatures and magnetic fields. From the measured complex frequency shift, the complex conductivity was calculated. The model for effective conductivity in the mixed state was fitted to the complex conductivity data and the values of upper critical fields Bc2(T) and depinning frequencies ω0 (T) have been obtained as fitted parameters.Mjerili smo mikrovalni odziv tankog filma visokotemperaturnog supravodiča YBa2Cu3O7−δ u širokom području temperatura i magnetskih polja. Iz izmjerenog kompleksnog frekventnog pomaka izračunali smo kompleksnu vodljivost. Numeričkom prilagodbom modela efektivne vodljivosti u miješanom stanju odredili smo vrijednosti gornjeg kritičnog polja Bc2 (T) i frekvencije opuštanja ω0(T)

Excitation of Spin Waves in Superconducting Ferromagnets

This Letter presents a theoretical analysis of propagation of spin waves in a superconducting ferromagnet. The surface impedance was calculated for the case when the magnetization is normal to the sample surface. We found the frequencies at which the impedance and the power absorption have singularities related to the spin wave propagation, and determined the form of these singularities. With a suitable choice of parameters, there is a frequency interval in which two propagating spin waves of the same circular polarization are generated, one of them having a negative group velocity.Comment: 4 pages, 2 figures, submitted to PR

Transport, magnetic and superconducting properties of RuSr2RCu2O8 (R= Eu, Gd) doped with Sn

Ru{1-x}Sn{x}Sr2EuCu2O8 and Ru{1-x}Sn{x}Sr2GdCu2O8 have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the dc Hall measurements. The magnetic ordering temperature T_m is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature T_c accompanied with the increase of the upper critical field B_c2, indicating an increased disorder in the system and a reduced scattering length of the conducting holes in CuO2 layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in CuO2 layers, which represent the main conductivity channel. Most of the electrons in RuO2 layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in RuO$_2$ layers that exhibit colossal magnetoresistance.Comment: 10 pages, 9 figure

Unconventional charge order in a co-doped high-Tc superconductor

Charge-stripe order has recently been established as an important aspect of cuprate high-Tc superconductors. However, owing to the complex interplay between competing phases and the influence of disorder, it is unclear how it emerges from the parent high-temperature state. Here we report on the discovery of an unconventional ordered phase between charge-stripe order and (pseudogapped) metal in the cuprate La1.8xEu0.2SrxCuO4. We use three complementary experiments—nuclear quadrupole resonance, nonlinear conductivity and specific heat—to demonstrate that the order appears through a sharp phase transition and exists in a dome-shaped region of the phase diagram. Our results imply that the new phase is a state, which preserves translational symmetry: a charge nematic. We thus resolve the process of charge-stripe development in cuprates, show that this nematic phase is distinct from high-temperature pseudogap and establish a link with other strongly correlated electronic materials with prominent nematic order

Microwave response of thin niobium films under perpendicular static magnetic fields

The microwave response of high quality niobium films in a perpendicular static magnetic field has been investigated. The complex frequency shift was measured up to the upper critical fields. The data have been analyzed by the effective conductivity model for the type-II superconductors in the mixed state. This model is found to yield consistent results for the coherence lengths in high-kappa superconducting samples, and can be used with HTSC even at temperatures much below T_c. It is shown that for samples with high values of depinning frequency, one should measure both components of the complex frequency shift in order to determine the flow resistivity. The thick Nb film (160 nm) has low resistivity at 10 K, comparable to the best single crystals, and low kappa value. In contrast, the thinnest (10 nm) film has kappa ~ 9.5 and exhibits a high depinning frequency (~20 GHz). The upper critical field determined from microwave measurements is related to the radius of nonoverlaping vortices, and appears to be larger than the one determined by the transition to the normal state.Comment: 8 pages, 7 figures; submitted to PRB; measured rho_n; changes due to the referees' comments (abstract, conclusions, extended introduction

General solution for the complex frequency shift in microwave measurements of thin films

Perturbation of a microwave cavity by a small sample with variable dielectric, magnetic, or conducting properties is considered. The complex frequency shift is derived in terms of a volume integral, or equivalently, in terms of a surface integral. These are used to obtain a general formula for thin films in the microwave electric field maximum. The complex frequency shift depends on the depolarization factor of the film and on its thickness in a nontrivial way. The previously known expressions for the complex frequency shift are shown to be good approximations of the present solution in the low and high conductivity limits. Our formula is applied to calculate the signal shapes in superconducting films of various geometric parameters and conductivities. It is shown that a diversity of signal shapes can result, and experimental support of those shapes is provided. The role of the dielectric substrate on which the thin film is grown is simply reduced to an asymmetry effect

Two component butterfly hysteresis in Ru1222 ruthenocuprate

We report detailed studies of the ac susceptibility butterfly hysteresis on the Ru1222 ruthenocuprate compounds. Two separate contributions to these hysteresis have been identified and studied. One contribution is ferromagnetic-like and is characterized by the coercive field maximum. Another contribution, represented by the so called inverted maximum, is related to the unusual inverted loops, unique feature of Ru1222 butterfly hysteresis. The different nature of the two identified magnetic contributions is proved by the different temperature dependences involved. By lowering the temperature the inverted peak gradually disappears while the coercive field slowly raises. If the maximum dc field for the hysteresis is increased, the size of the inverted part of the butterfly hysteresis monotonously grows while the position of the peak saturates. In reaching saturation exponential field dependence has been demonstrated to take place. At T = 78 K the saturation field is 42 Oe.Comment: 5 pages, 5 figure