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

Magnetostrictive behaviour of thin superconducting disks

Flux-pinning-induced stress and strain distributions in a thin disk superconductor in a perpendicular magnetic field is analyzed. We calculate the body forces, solve the magneto-elastic problem and derive formulas for all stress and strain components, including the magnetostriction $\Delta R/R$. The flux and current density profiles in the disk are assumed to follow the Bean model. During a cycle of the applied field the maximum tensile stress is found to occur approximately midway between the maximum field and the remanent state. An effective relationship between this overall maximum stress and the peak field is found.Comment: 8 pages, 6 figures, submitted to Supercond. Sci. Technol., Proceed. of MEM03 in Kyot

Shape Distortion by Irreversible Flux-Pinning-Induced Magnetostriction

Exact analytical results are obtained for the flux-pinning-induced magnetostriction in cylindrical type-II superconductors placed in parallel magnetic field. New modes of irreversible deformation are found: In contrast to the circular cylinder where shape is conserved, it is shown that a square cross-section deforms with considerable distortion. During a field cycle both concave, convex, and even more complicated distortions are predicted. Strong implications for dilatometric measurements on crystals are emphasized. The main results are valid for any critical-state model, j_c = j_c(B).Comment: 4 pages, 4 graph

Time evolution of the magnetic properties of la0.5R0.5Ba2Cu3O6+x(R = rare earth) high-Tc superconductors

The magnetic properties of the mixed high-Tc superconductors Ea0.5R0.5Ba2Cu3O6+x (R - rare earth) are studied after prolonged 'aging' at room temperature (RT) for 1 year. Enhancement of the superconducting properties comprising the increase of the inhomogeneous diamagnetic signal for members of the series with the larger R-ion radius is detected after RT 'aging'. For the members with the larger R-ion radius the diamagnetic signal has been come more stronger whereas for the members with the smaller R-ion radius the time evolution of the superconducting properties remained almost the unchanged and the diamagnetic signal slightly decreases after 'aging'. The growth of the EPR intensity of localized Cu2+ centers complying with the rise of the normal-state magnetic susceptibility after prolonged storage at RT, is detected. The time evolution effects are related to slow ion diffusion processes that can be induced by stress-relaxation in the mixed Ea0.5R0.5Ba2Cu3O6+x structure, most pronounced for large R-ion radius. © 1999 Elsevier Science B.V. All rights reserved

Time evolution of copper defects in the mixed phase La0.5Gd0.5Ba2Cu3Oy

XRD, magnetic and EPR studies of the mixed phase La0.5Gd0.5Ba2Cu3Oy high-Tc superconductor after prolonged (one year) `aging' at room temperature are reported. Within this time period a pronounced change of the superconducting behavior and the homogeneity of the diamagnetic shielding signal accompanied by substantial structural changes, reduction of the impurity phase BaCuO2+x and increase of the EPR spectrum's intensity of Cu2+ magnetic defects is detected. The `aging' effects are related to strain-relaxation taking place during room temperature annealing that induces the formation of Cu2+ defect centers

Magnetostriction studies in nano-crystalline zinc ferrite thin films by strain modulated ferromagnetic resonance

The magnetoelastic properties of nano-crystalline zinc ferrite (ZnFe2O4) thin films prepared by Pulse laser deposition on amorphous fused quartz substrates have been investigated by means of the strain-modulated ferromagnetic resonance, as a function of the substrate temperature during the deposition, and as a function of the annealing temperature. Magnetoelastic constants reveal the same trends as the magnetization, showing correlation between these two parameters. The results are similar to that obtained earlier for the Y3Fe5O12 ferrite. (C) 2018 Elsevier B.V. All rights reserved