Effect of contact geometry on magnetoresistance in CoPd-contacted carbon nanotubes

Abstract

We present local magnetoresistance measurements on carbon nanotubes contacted with the ferromagnetic alloy Co50 Pd50. A sample with contacts of nm, m exhibited the typical sharp switching expected at the coercive fields of the contacts. However, a sample with the same in-plane geometry but a thickness of 40 nm displayed a complicated switching behavior indicative of gradual domain wall rotation. In both samples, the contact widths were varied to control shape anisotropy. Further characterization of the contacts and similar contact-like structures via remanent state magnetic force microscopy suggested a single or few domain structure in the 10 nm thick contacts. The thicker contacts exhibited a complex domain structure characteristic of a hard or intermediate magnetic axis along the long axis of the contact, despite the effect of shape anisotropy. This result is discussed with respect to the influence of both thickness and in-plane geometry on competing anisotropy contributions within the device. The characterization allows for the pinpointing of precise dimensions that will determine the magnetic easy axis of contacts, thereby controlling magnetotransport.