3000 % high-field magnetoresistance in super-lattices of CoFe nanoparticles

TL;DR

This study reports an exceptionally large high-field magnetoresistance in super-lattices of CoFe nanoparticles, reaching up to 3000%, with unique temperature and voltage dependencies, attributed to localized paramagnetic moments.

Contribution

It demonstrates a record-high magnetoresistance in nanoparticle super-lattices and explores its unusual exponential voltage dependence and temperature behavior.

Findings

Magnetoresistance reaches up to 3000% between 1.8 and 10 K.

Magnetoresistance scales with magnetic field/temperature ratio.

Magnetoresistance disappears below 1.8 K.

Abstract

We report on magnetotransport measurements on millimetre-large super-lattices of CoFe nanoparticles surrounded by an organic layer. Electrical properties are typical of Coulomb blockade in three dimensional arrays of nanoparticles. A large high-field magnetoresistance, reaching up to 3000 %, is measured between 1.8 and 10 K. This exceeds by two orders of magnitude magnetoresistance values generally measured in arrays of 3d metals ferromagnetic nanoparticles. The magnetoresistance amplitude scales with the magnetic field / temperature ratio and displays an unusual exponential dependency with the applied voltage. The magnetoresistance abruptly disappears below 1.8 K. We propose that the magnetoresistance is due to some individual paramagnetic moments localized between the metallic core of the nanoparticles, the origin of which is discussed.