Double Percolation Transition in Superconductor-Ferromagnet Nanocomposites

Abstract

A double percolation transition is identi…ed in a binary network composed of nanoparticles of MgB 2 superconductor and CrO 2 half-metallic ferromagnet. Anomalously high-resistance or insulating state, as compared to the conducting or superconducting states in single-component systems of either constituent, is observed between two distinct percolation thresholds. This double percolation e¤ect, which is especially pronounced at liquid helium temperatures, is controlled by composite volume fraction and originates from the suppressed interface conduction and tunneling between nanoparticles of di¤erent species. We investigate the scaling behavior near both percolation thresholds, and determine the distinct critical exponents associated with two di¤erent types of transitions.

The critical current reaction on hydrostatic pressure of a superconductor–semimetal composite

“…It is known that the electrical transport characteristics of composites depend on the structure of a conductive cluster arising in the composite, in particular in the case of components with very different conductivity. 27 If an infinite percolation cluster for the highly conductive phase is broken, the transport properties of the composite are determined by the high-resistance phase. In the composite MgB 2 -LCMO, the high-resistance phase is LCMO manganite.…”

“…Above the percolation threshold the transport properties of the composite are determined by the passage of current through the MgB 2 -LCMO-MgB 2 chains. Based on the standard percolation model, 27,28 small amounts ($20 vol. %) of the highresistance LCMO phase cannot break the infinite cluster of the low-resistance MgB 2 phase.…”

Transport Properties of La0.7Sr0.3MnO3/MgB2 Random Nanocomposites

“…The creation of such a medium can be realized artificially by means of a direct contact of various materials with superconducting material. As a result, new compounds with unique characteristics not realized for 'parent' components can be obtained [1][2][3][4][5][6][7]. In particular, interest to superconducting proximity effect in S-N structures is initiated by the possibilities of new applications of these structures as novel functional elements of nanoelectronics [1][2][3].…”

“…Overall, the superconducting proximity effect was observed in halfmetallic manganites being in contact with Ss of different symmetries: as s-wave symmetry Pb, Nb, MgB 2 [12][13][14], as well as d-wave symmetry, cuprates [8][9][10][11]16,17], of the order parameter. Yet, the question, what mechanism is responsible for the transfer of Cooper pairs through the hmF remains still open and is the subject of intensive discussions [1,3,4,5].…”

Double percolation effects and fractal behavior in magnetic/superconducting hybrids

“…Percolation phenomena are present in a wide variety of disordered systems, ranging from random networks [1] to nanomaterials [2], granular superconductors [3,4] or perpendicular magnetic anisotropy (PMA) materials [5]. Theoretical understanding of these phenomena has evolved from the classical analysis of simple regular lattices [6,7] to more complex situations [8].…”