Tunnel magnetoresistance of thin‐film nanogranular metal–dielectric composites (x)Ni–(1−x)PNBZT

Abstract

Thin‐film nanogranular metal–dielectric composites (x)Ni–(1−x)[Pb0.81Sr0.04(Na0.5Bi0.5)0.15][(Zr0.575Ti0.425)]O3 (denoted as (x)Ni–(1−x)PNBZT) were prepared by the ion‐beam sputtering method. The X‐ray diffraction analysis has revealed the presence of two phases in the composites: a crystalline Ni phase and an amorphous PNBZT phase. Composites (x)Ni–(1−x)PNBZT with compositions below the percolation threshold manifest a negative magnetoresistance, whose highest values of 0.13% at 287 K and 0.78% at 77 K are observed near the percolation threshold at хс = 35 at.% for a composite sample of 0.31Ni–0.69PNBZT placed in a constant magnetic field with the strength of 8000 Oe. The magnetoresistance of the composites (x)Ni–(1−x)PNBZT is increased with the growth of the constant magnetic field strength, and the dependence remains the same as a polarity of the magnetic field is varied. The charge transport in the composites (x)Ni–(1−x)PNBZT over a temperature interval of 188–287 K is shown to be attributed to the inelastic resonant tunneling of electrons through energy barriers in a dielectric layer of PNBZT between crystalline ferromagnetic nanogranules of Ni. Therefore, to explain the experimentally established regularities of the negative magnetoresistance, the tunnel magnetoresistance model has been used.