Index of content:
Volume 95, Issue 6, 15 March 2004
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
95(2004); http://dx.doi.org/10.1063/1.1649462View Description Hide Description
Based on phase separation between metallic and insulating domains, the evolution of magnetoresistance in mixed-phase polycrystalline manganites, as a function of temperature, has been modeled via a bond-disordered random resistor network. The tunnelingbond is introduced in the resistor network to account for the contribution from grain boundaries, where the energy barrier is formed. The model is analytically worked out by means of the effective-medium approximation. Compared with the transport in single-phase ferromagnetic-ordered polycrystal, the transport in mixed-phase polycrystal is governed by not only the properties of grain boundaries but also the competing metallic and insulating phases. The fraction of tunnelingbonds strongly depends on the temperature and external magnetic field. An active tunneling model is thus established in mixed-phase polycrystalline manganites. Within our model, the effect of crystallinity on the temperature dependence of magnetoresistance in mixed-phase polycrystalline manganites is well explained.
95(2004); http://dx.doi.org/10.1063/1.1650532View Description Hide Description
A model is presented in this article to investigate the dependence of effective magnetostriction of the magnetostrictive composites on the parameters of components including the elastic modulus, permeability, and volume fraction, etc. Concentrating on the two-component magnetostrictive composites and choosing the two components to be general magnetostrictive materials, this model yields, analytically, the effective magnetostriction of composites by means of the method of complex potential. In terms of the analysis of this model, the magnetostrictive composites can be roughly divided into two kinds. One kind is that the matrix material is nonmagnetic or a material with very low magnetostriction, in which the effective magnetostriction is independent of the permeability of components. Another kind is the case in which the two components have close magnetostriction, and the effective magnetostriction of the composites generally depends on the elastic and the magnetic parameters of both components and the volume fraction. Unlike the first kind of composite, in a certain range, effective magnetostriction of this kind of composite can be improved by increasing the permeability of matrix. In addition, dependence of the effective magnetostriction on the other parameters of the components has also been discussed systematically. To evaluate the accuracy of this model, comparisons are made between the theoretical values and the experimental results published in the literature, which indicate that predictions of this model agree qualitatively with the experimental data.