Magnetoresistance of atomic-scale electromigrated nickel nanocontacts

Keane, Zachary; Yu, Lam H.; Natelson, Douglas

doi:10.1063/1.2172232

Cited by 37 publications

(47 citation statements)

References 17 publications

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“…To make the junction suitable for contact by macroscopic probes, two gold electrodes are deposited over the edges of the junction in a second lithography step, following the procedure described in ref. 19 . The samples are then placed in a probe station that was pumped down and immersed in a liquid helium bath until the sample reached a temperature close to 4.2 K. Under these conditions, the controlled electromigration process 14,19 was performed, decreasing the size of the junction to the atomic scale.…”

Section: Appendix A: Methodsmentioning

confidence: 99%

“…For the temperature-dependence measurements, the contacts were produced by the controlled electromigration at 4.2K of 100-nm-wide junctions fabricated by electron beam lithography 19 . In both cases, the spectroscopic curves were obtained by the addition of an a.c. voltage with a peak-power amplitude of 1mV and a frequency of 1 kHz to the d.c. bias voltage to allow the lock-in detection of the differential conductance.…”

Section: Appendix A: Methodsmentioning

confidence: 99%

“…To preserve the atomic stability of the junction while changing the temperature 19 , we used an EBJ such as the one shown in the inset of Fig. 3b.…”

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confidence: 99%

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The Kondo effect in ferromagnetic atomic contacts

Calvo

Fernández-Rossier

Palacios

et al. 2009

Nature

143

168

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Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk, electronic conduction in these materials takes place mainly through the s and p electrons, whereas the magnetic moments are mostly in the narrow d-electron bands, where they tend to align. This general picture may change at the nanoscale because electrons at the surfaces of materials experience interactions that differ from those in the bulk. Here we show direct evidence for such changes: electronic transport in atomic-scale contacts of pure ferromagnets (iron, cobalt and nickel), despite their strong bulk ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of local magnetic moments by the conduction electrons below a characteristic temperature 1 . The Kondo effect creates a sharp resonance at the Fermi energy, affecting the electrical properties of the system;this appears as a Fano-Kondo resonance 2 in the conductance characteristics as observed in other artificial nanostructures 3,4,5,6,7,8,9,10,11 . The study of hundreds of contacts shows material-dependent lognormal distributions of the resonance width that arise naturally from Kondo theory 12 . These resonances broaden and disappear with increasing temperature, also as in standard Kondo systems 4,5,6,7 . Our observations, supported by calculations, imply that coordination changes can significantly modify magnetism at the nanoscale. Therefore, in addition to standard micromagnetic physics, strong electronic correlations along with atomic-scale geometry need to be considered when investigating the magnetic properties of magnetic nanostructures.Atomic-scale contacts can be fabricated by techniques such as scanning tunnelling microscopy 13 or the use of electromigrated break junctions (EBJs) 14 , where the size of a macroscopic contact between two leads is reduced until they are in contact through only a few atoms and, eventually, through only one. The conductance of metallic monatomic contacts is known to be around 2G 0 , where G 0 = e 2 /h is the spin-resolved quantum of conductance 13 (e being the elementary charge and h Planck ′ s constant). To identify the atomic contacts, histograms are constructed from the evolution of the conductance recorded during the breaking of different contacts (Fig. 1a, b). The position of the first peak of these histograms is identified as the conductance of the monatomic contact. For iron, cobalt and nickel, the conductance is larger than 2G 0 owing to the contribution of the sp and d orbitals to the transmission 15,16,17 .We have studied the low-temperature conductance characteristics of hundreds of atomic-scale contacts of the three transition-metal ferromagnets iron, cobalt and nickel using a home-built STM. More than the 80% of the differential conductance (dI/dV ) curves at the monatomic contact show peaks or dips around zero bias such as those shown in Fig. 1c, which are very similar to those observed in STM spectroscopy of single magnetic adatoms on non-magnetic surfaces 9,10,11 . Thus, as in the case of these Kondo systems, we ca...

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Section: Appendix A: Methodsmentioning

confidence: 99%

Section: Appendix A: Methodsmentioning

confidence: 99%

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The Kondo effect in ferromagnetic atomic contacts

Calvo

Fernández-Rossier

Palacios

et al. 2009

Nature

143

168

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“…1,2 The transport counterpart of MAE is anisotropic magnetoresistance ͑AMR͒, i.e., the dependence of the resistance on the angle between the magnetization and the current flow. Whereas AMR in bulk was known back in the 19th century and is a rather small effect, the recent observation of AMR in a variety of low dimensional systems, [3][4][5][6][7][8][9][10][11][12] largely exceeding bulk values, has opened a new research venue in the field of spin-polarized quantum transport. Very large AMR has been reported in planar tunnel junctions ͓tunneling anisotropic magnetoresistance ͑TAMR͔͒ with a variety of electrode and barrier materials.…”

Section: Introductionmentioning

confidence: 99%

“…Very large AMR has been reported in planar tunnel junctions ͓tunneling anisotropic magnetoresistance ͑TAMR͔͒ with a variety of electrode and barrier materials. [3][4][5][6][7][8] Enhanced AMR has also been observed in atomic sized contacts, both in the tunnel regime ͑TAMR͒ and in the contact ͑or ballistic 13 ͒ regime ͓ballistic anisotropic magnetoresistance ͑BAMR͔͒, 14 for Py, 9 Fe, 10 Ni, 11 and Co. 12 Additionally, GaMnAs islands in the Coulomb blockade regime show electrically tunable AMR. 15 Thus, a wide range of nanostructures made from different materials display enhanced AMR.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic magnetoresistance in nanocontacts

2008

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We present ab initio calculations of the evolution of anisotropic magnetoresistance ͑AMR͒ in Ni nanocontacts from the ballistic to the tunnel regime. We find an extraordinary enhancement of AMR, compared to bulk, in two scenarios. In systems without localized states, such as chemically pure break junctions, large AMR only occurs if the orbital polarization of the current is large, regardless of the anisotropy of the density of states. In systems that display localized states close to the Fermi energy, such as a single electron transistor with ferromagnetic electrodes, large AMR is related to the variation of the Fermi energy as a function of the magnetization direction.

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