In situ magnetoresistance of Ni nanocontacts

Abstract

Magnetoresistance properties of Ni nanocontacts in the ballistic quantum regime are investigated in situ during closure and opening of electrochemically grown planar electrodes. The magnitude of conductance change when sweeping the magnetic field is of the order of the quantum conductance e2/h for conductance values spanning 1–100 quanta. The relative orientation of electric current and applied magnetic field changes the magnetoresistance sign, with symmetry properties reminiscent of bulk anisotropy magnetoresistance. Ex situ investigations of samples of higher conductance values, of the order of 1000 quanta, unambiguously show the analogy with bulk anisotropy magnetoresistance.

Quantized magnetoresistance in atomic-size contacts

“…1a) 10,19 . A Co fi lm was then electrodeposited to close the gap between the electrodes using a cobalt sulphate electroplating bath under constant voltage conditions.…”

Magnetoresistance of atomic-scale electromigrated nickel nanocontacts

“…It is therefore of much interest to examine constrictions fabricated in a geometry that minimizes these effects and allows temperature-dependent studies of junction magnetoresistances. Recent experiments along these lines have used mechanical break junctions [4], planar electrochemically grown junctions [5], ballistic nanopores [6], and ion-beam-formed constrictions [7] In this Letter we report measurements of the magnetoresistance through few-atom and single-atom contacts between planar Ni electrodes, as well as planar Ni-Ni tunnel junctions. Junctions are fabricated by a combination of electron beam lithography and controlled electromigration.…”

Anisotropic Magnetoresistance and Anisotropic Tunneling Magnetoresistance due to Quantum Interference in Ferromagnetic Metal Break Junctions

“…PACS numbers: 72.25.Ba; 73.63.Rt; 75.75.+a The magnetoresistance properties of nanometer-scale magnetic devices can be quite different from those of larger samples. One aspect of this difference has been explored extensively in previous experiments -the resistance of magnetic domain walls created when the magnetic moment direction in one magnetic electrode is rotated relative to the moment in a second electrode [1,2,3,4,5,6,7,8,9]. Here we focus on a different aspect of the physics of magnetoresistance in nanoscale magnetic contacts -the anisotropic magnetoresistance (AMR) that arises when the magnetization throughout a device is rotated uniformly so as to change the angle between the direction of current flow and the magnetic moment.…”

“…By making detailed studies of resistance as a function of field angle using mechanically-stable permalloy contacts, we show that the size of the AMR signal at low temperature can increase dramatically as the contact cross section is narrowed to the nanometer-scale regime. Even more strikingly, we find that point contacts which are completely broken, so as to enter the tunneling regime, also exhibit a tunneling anisotropic magnetoresistance effect (TAMR) as large as 25% when the magnetic-moment directions in the two contacts are rotated together while remaining parallel.Magnetostriction and magnetostatic forces can alter the geometry of nanoscale junctions as the magnetic field is varied, and produce artifacts in the resistance, so experiments must be designed to minimize these effects [5,6,7]. For this reason, our contacts are firmly attached to a non-magnetic silicon substrate and are measured entirely at low temperature to suppress thermally-driven surface diffusion of metal atoms.…”

“…Magnetostriction and magnetostatic forces can alter the geometry of nanoscale junctions as the magnetic field is varied, and produce artifacts in the resistance, so experiments must be designed to minimize these effects [5,6,7]. For this reason, our contacts are firmly attached to a non-magnetic silicon substrate and are measured entirely at low temperature to suppress thermally-driven surface diffusion of metal atoms.…”