Vortex liquid correlations induced by in-plane field in underdoped Bi2Sr2CaCu2O8+d

By measuring the Josephson Plasma Resonance, we have probed the influence of an in-plane magnetic field on the pancake vortex correlations along the c-axis in heavily underdoped Bi2Sr2CaCu2O8+d (Tc = 72.4 +/- 0.6 K) single crystals both in the vortex liquid and in the vortex solid phase. Whereas the in-plane field enhances the interlayer phase coherence in the liquid state close to the melting line, it slightly depresses it in the solid state. This is interpreted as the result of an attractive force between pancake vortices and Josephson vortices, apparently also present in the vortex liquid state. The results unveil a boundary between a correlated vortex liquid in which pancakes adapt to Josephson vortices, and the usual homogeneous liquid.Comment: 2 pages, submitted to the Proceedings of M2S HTSC VIII Dresde

Vortex Solid-Liquid Transition in Bi2_{2}Sr2_{2}CaCu2_{2}O8+δ_{8+\delta} with a High Density of Strong Pins

The introduction of a large density of columnar defects in %underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ crystals does not, at sufficiently low vortex densities, increase the irreversibility line beyond the first order transition (FOT) field of pristine crystals. At such low fields, the flux line wandering length $r_{w}$ behaves as in pristine %Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ crystals. Next, vortex positional correlations along the $c$--axis in the vortex Bose glass at fields above the FOT are smaller than in the low--field vortex solid. Third, the Bose-glass-to-vortex liquid transition is signaled by a rapid decrease in c-axis phase correlations. These observations are understood in terms of the ``discrete superconductor'' model.Comment: 4 pages, 4 figures Submitted to Phys. Rev. B Rapid Comm. 16-1-2004 Revised version 18-3-200

Ferromagnetic Resonance Studies of La0.67\text{}_{0.67}Ca0.33\text{}_{0.33}MnO3\text{}_{3} Film under Stress

Ferromagnetic resonance spectra of the La$\text{}_{0.67}$Ca$\text{}_{0.33}$MnO$\text{}_{3}$ ferromagnetic film deposited onto the x-cut LiNbO$\text{}_{3}$ substrate were investigated in a wide temperature range. The strain was mechanically introduced into the film using a special holder configuration. This leads to a shift of resonance field with respect to that of the as-grown sample. Analysis of the magnetic resonance shift, induced by a mechanical stress, allowed us to determine the magnetostriction constant λ$\text{}_{100}$. The magnetostriction determined in this way versus saturation magnetization could be well described by the Callen and Callen theory suggesting the domination of the single ion crystal field interaction in the sample being in the ferromagnetic state

Ferromagnetic Resonance Studies of La 0.67

Ferromagnetic resonance spectra of the La$\text{}_{0.67}$Ca$\text{}_{0.33}$MnO$\text{}_{3}$ ferromagnetic film deposited onto the x-cut LiNbO$\text{}_{3}$ substrate were investigated in a wide temperature range. The strain was mechanically introduced into the film using a special holder configuration. This leads to a shift of resonance field with respect to that of the as-grown sample. Analysis of the magnetic resonance shift, induced by a mechanical stress, allowed us to determine the magnetostriction constant λ$\text{}_{100}$. The magnetostriction determined in this way versus saturation magnetization could be well described by the Callen and Callen theory suggesting the domination of the single ion crystal field interaction in the sample being in the ferromagnetic state

Study of Si-Implanted and Thermally Annealed Layers of Silicon by Using X-ray Grazing Incidence Methods

This paper reports on the study of structural modifications induced by the implantation process and by the subsequent thermal annealing in near-surface layers of Si single crystals implanted with Si$\text{}^{2+}$ ions of energy 140 keV and doses from 1×10$\text{}^{15}$ to 1× 10$\text{}^{16}$ ions/cm$\text{}^{2}$. The grazing incidence X-ray diffraction and X-ray reflectivity measurements were applied to determine the thickness and structural composition of the damaged layers. The fitted electron density profiles indicated an existence of an interfacial layer with density higher than the density of Si matrix or near-surface oxide layer. Formation of polycrystalline phases of silicon and silicon oxides is discussed in dependence on the conditions of annealing treatment and implantation dose

Optimization of the Superconducting Properties of Laser Ablated YBa2Cu3O7−δYBa_2Cu_3O_{7-δ} Films on CeO2CeO_2-Buffered Sapphire

We use pulsed laser deposition to grow $YBa_2Cu_3O_{7-δ}$ (YBCO) superconducting films for microwave applications. The films are grown on R-cut sapphire substrates, with $CeO_2$ buffer layers, which are re-crystallized at high temperature prior to YBCO growth. Using the atomic force microscopy (AFM) and X-ray diffractometry we determine the optimal temperature for recrystallization (1000°C) and the optimal buffer layer thickness (30 nm). The properties of YBCO films of various thickness, grown on the optimized $CeO_2$ buffer layers, are studied using several methods, including AFM, magnetooptical imaging, and transport experiments. The YBCO film roughness is found to increase with the increasing film thickness, but the magnetic flux penetration in the superconducting state remains homogeneous. The superconducting parameters (the critical temperature and the critical current density) are somewhat lower than the similar parameters for YBCO films deposited on mono-crystalline substrates

La0.7\text{}_{0.7}Sr0.3\text{}_{0.3}MnO3\text{}_{3} Thin-Film Grain-Boundary Junctions on a Bi-Crystal Substrate

Transport properties of 10μm to 30μm wide grain-boundary junctions ion-etched in thin colossal magnetoresistance La$\text{}_{0. 7}$Sr$\text{}_{0.3}$MnO$\text{}_{3}$ films deposited on a SrTiO$\text{}_{3}$ bi-crystal were investigated. We have measured the current-voltage characteristics in the temperature range from 4.2 K to 300 K without applied magnetic field, as well as the magnetoresistance at magnetic fields up to±10 kOe directed parallel to the film surface, both perpendicular and parallel to the direction of current flow through the junctions. The investigated junctions have nonlinear current-voltage characteristics in this temperature range and consist of several magnetic domains. The maximum magnetoresistance (R(H)-R $\text{}_{max}$)/R$\text{}_{max}$, measured at 1 kOe was -17.6% at 4.1 K

Atomic Order and the Interaction of Electronic and Magnetic Subsystems in Epitaxial LaSr(Ca)MnO Films

We have investigated the structure, and electric, optical, and magnetic properties of LaSr(Ca)MnO films containing atomic clusters of various types coherently built into the basic crystallographic matrix. Below the transition to the metallic state, the electrical conductivity of the films is determined by tunneling of charge carriers between metallic clusters. We have found that for each sample there exists a threshold value of magnetic ordering, above which the magnetic subsystem starts to affect actively the film conductivity. The observed increase of conductivity with decreasing temperature is caused by the fact that in the process of magnetic ordering of the samples the cluster size and concentration of metallic phase increase. Experimental results are in agreement with theoretical calculations