Three terminal capacitance technique for magnetostriction and thermal expansion measurements

An instrument has been constructed to measure a large range of magnetostriction and thermal expansion between room temperature and 4 K in a superconductive split-coil magnet, that allows investigation in magnetic fields up to 12 T. The very small bulk samples (up to 1 mm in size) as well as big ones (up to 13 mm) of the irregular form can be measured. The possibility of magnetostriction investigation in thin films is shown. A general account is given of both electrical and the mechanical aspects of the design of capacitance cell and their associated electronic circuitry. A simple lever device is proposed to increase the sensitivity twice. The resulting obtained sensitivity can be 0.5 Angstrom. The performance of the technique is illustrated by some preliminary measurements of the magnetostriction of superconducting MgB2, thermal expansion of (La0.8Ba0.2)0.93MnO3 single crystal and magnetoelastic behavior of the Ni/Si(111) and La0.7Sr0.3CoO3/SAT0.7CAT0.1LA0.2(001) cantilevers.Comment: 6 pages, 6 figures, journal pape

Two and Three Dimensional Incommensurate Modulation in Optimally-Doped Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta}

X-ray scattering measurements on optimally-doped single crystal samples of the high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ reveal the presence of three distinct incommensurate charge modulations, each involving a roughly fivefold increase in the unit cell dimension along the {\bf b}-direction. The strongest scattering comes from the well known (H, K$\pm$ 0.21, L) modulation and its harmonics. However, we also observe broad diffraction which peak up at the L values complementary to those which characterize the known modulated structure. These diffraction features correspond to correlation lengths of roughly a unit cell dimension, $\xi_c$$\sim$20 $\AA$ in the {\bf c} direction, and of $\xi_b$$\sim$ 185 $\AA$ parallel to the incommensurate wavevector. We interpret these features as arising from three dimensional incommensurate domains and the interfaces between them, respectively. In addition we investigate the recently discovered incommensuate modulations which peak up at (1/2, K$\pm$ 0.21, L) and related wavevectors. Here we explicitly study the L-dependence of this scattering and see that these charge modulations are two dimensional in nature with weak correlations on the scale of a bilayer thickness, and that they correspond to short range, isotropic correlation lengths within the basal plane. We relate these new incommensurate modulations to the electronic nanostructure observed in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ using STM topography.Comment: 8 pages, 8 figure

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means of magnetization measurements in the temperature range between 1.95 K and Tc, in an external magnetic field up to 9 T. Flux jumps were found in the temperature range 1.95 K - 6 K, with the external magnetic field parallel to the c axis of the investigated sample. The effect of sample history on magnetic flux jumping was studied and it was found to be well accounted for by the available theoretical models. The magnetic field sweep rate strongly influences the flux jumping and this effect was interpreted in terms of the influence of both flux creep and the thermal environment of the sample. Strong flux creep was found in the temperature and magnetic field range where flux jumps occur suggesting a relationship between the two. The heat exchange conditions between the sample and the experimental environment also influence the flux jumping behavior. Both these effects stabilize the sample against flux instabilities, and this stabilizing effect increases with decreasing magnetic field sweep rate. Demagnetizing effects are also shown to have a significant influence on flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.

Analysis of the Thermal and Magnetic Properties of Amorphous Fe 61Co10Zr2.5Hf2.5Me2W2B20 (Where Me = Mo, Nb, Ni Or Y) Ribbons

The paper presents the results of structural and magnetic properties and thermal stability for a group of functional materials based on Fe61Co10Zr2.5Hf2.5Me2W2B20 (where Me = Mo, Nb, Ni or Y). Samples were obtained in the form of ribbons using melt-spinning method. The X-ray diffraction patterns of investigated samples confirmed their amorphous structure. Based on the analysis of DSC curves characteristic temperatures: glass forming temperature (Tg), crystallization temperature (Tx) and temperature range of the supercooled liquid ΔTx were determined. Small addition of transition metals elements has strong influence on magnetic and thermal parameters of studied materials. The comprehensive studies revealed that in terms of magnetic properties the Ni-addition resulted in highest reduction in coercivity and anisotropy field