Evolution of magnetoresistance in electromigrated ferromagnetic break junctions

摘要: Recently, magnetotransport measurements of magnetic nanocontacts have led to a better understanding of the interactions between spin-polarized charge carriers and magnetization taking place at extremely small length scales. Here, we present the evolution of magnetoresistance (MR) in clean electrical break junctions. Ferromagnetic nanocontacts with variable constriction width are fabricated by performing in-situ controlled electromigration of notched magnetic half ring structures in UHV. Low temperature MR measurements, in agreement with micromagnetic simulations, indicate that the dominant contribution in Py (Ni{sub 80}Fe{sub 20}) contacts down to the size of a few nm is anisotropic magnetoresistance (AMR). Moreover, Ni shows enhanced AMR in constrictions approaching the atomic limit and high tunnelling anisotropic magnetoresistance (TAMR) after carefully opening the contact, suggesting that material-specific parameters such as the electron mean free path play a crucial role. By analyzing the angle-dependent MR we can furthermore extract the domain wall pinning strength of the constriction as a function of its size down to the atomic scale.