Spin-dependent resonant quantum tunneling between magnetic nanoparticles on a macroscopic length scale

Abstract

Macroscopic quantum phenomena are common features observed in superconductors, superfluid helium, and Bose-Einstein condensates. However, most of quantum transport studies are based on a small number of dots and are not in long-range electron transport length scale. Here we show that spin-dependent resonant quantum tunneling is achieved in the macroscopic length scale (a few millimeters) corresponding to an array of up to ${10}^{4}$ junctions in a series consisting of Co nanoparticles embedded in an oxygen-deficient TiO${}_{2}$ matrix. This phenomenon is observed by magnetoresistance measurements at 5 K in a Coulomb blockade regime. We further present a model based on resonant spin-polarized quantum tunneling of electrons of Co particles. It occurs through resonant continuous spin-polarized defect band states located near the Fermi level of the defective TiO${}_{2}$, which acts as a magnetic tunnel barrier. These results might be potentially useful for future designs of spintronic quantum devices.