Giant orbital moments are responsible for the anisotropic magnetoresistance of atomic contacts

TL;DR

This paper investigates the anisotropic magnetoresistance in atomic contacts, revealing that giant orbital moments on central atoms cause hysteretic conductance switching, challenging traditional models based on simple band structures.

Contribution

It demonstrates experimentally and theoretically that giant orbital moments induce anisotropic magnetoresistance and hysteretic switching in atomic contacts, offering a new understanding beyond conventional models.

Findings

Hysteretic conductance switch observed in iron break junctions.

Giant orbital moments are present on low-coordinated atoms.

The behavior contradicts traditional band-structure models.

Abstract

We study here, both experimentally and theoretically, the anisotropy of magnetoresistance in atomic contacts. Our measurements on iron break junctions reveal an abrupt and hysteretic switch between two conductance levels when a large applied field is continuously rotated. We show that this behaviour stems from the coexistence of two metastable electronic states which result from the anisotropy of electronic interactions responsible for the enhancement of orbital magnetization. In both states giant orbital moments appear on the low coordinated central atom in a realistic contact geometry. However they differ by their orientation, parallel or perpendicular, with respect to the axis of the contact. Our explanation is totally at variance with the usual model based on the band structure of a monatomic linear chain, which we argue cannot be applied to 3d ferromagnetic metals.