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

¹  CEA, IRAMIS, SPCSI - Bâtiment 462, F-91191 Gif-sur-Yvette, France, EU
²  Laboratoire de Physique des Solides, Université Paris Sud, UMR 8502 - Bâtiment 510, F-91405 Orsay, France, EU
³  CEA, IRAMIS, SPEC - Bâtiment 772, Orme des Merisiers, F-91191 Gif-sur-Yvette, France, EU

Corresponding author: cyrille.barreteau@cea.fr

Received: 23 January 2008
Accepted: 26 May 2008

Abstract

We study here, both experimentally and theoretically, the anisotropy of magneto- resistance 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 propose 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 ferromagnetic metals.