Anisotropic magnetoresistance in nanocontacts

TL;DR

This paper uses ab initio calculations to study how anisotropic magnetoresistance (AMR) in Ni nanocontacts varies from ballistic to tunneling regimes, revealing conditions for large AMR enhancements related to orbital polarization and localized states.

Contribution

It provides new insights into the mechanisms driving large AMR in nanocontacts, distinguishing effects in systems with and without localized states.

Findings

Large AMR occurs with high orbital polarization in pure systems.

Localized states near Fermi energy lead to AMR variation with magnetization.

AMR is significantly enhanced compared to bulk in nanocontacts.

Abstract

We present ab initio calculations of the evolution of anisotropic magnetoresistance (AMR) in Ni nanocontacts from the ballistic to the tunnel regime. We find an extraordinary enhancement of AMR, compared to bulk, in two scenarios. In systems without localized states, like chemically pure break junctions, large AMR only occurs if the orbital polarization of the current is large, regardless of the anisotropy of the density of states. In systems that display localized states close to the Fermi energy, like a single electron transistor with ferromagnetic electrodes, large AMR is related to the variation of the Fermi energy as a function of the magnetization direction.