The quantum spin-valve in cobalt atomic point contacts

Chopra, Harsh Deep; Sullivan, Matthew R.; Armstrong, Jason N.; Hua, Susan Z.

doi:10.1038/nmat1510

Cited by 76 publications

(60 citation statements)

References 36 publications

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“…We will discuss the effect of noncollinear magnetism on ballistic transport through such a junction, specifically keeping in mind tunneling-to-contact STM (Refs. [3][4][5][6][7][8] and mechanically controllable break-junctions 40 experiments. In particular, we investigate the changes in the transport properties upon changing the distance between the two Mn atoms, while keeping all other interatomic distances fixed at their equilibrium "semi-infinite" values.…”

Section: The Comentioning

confidence: 99%

“…2 In this respect, a great advantage is given by the use of scanning tunneling microscopy (STM) experiments, in which a tip can approach and contact single atoms or molecules on a surface. [3][4][5][6][7][8] In such experiments, it has been possible to measure the conductance as a function of tip-sample distance from the tunneling to the contact regime. Due to the promise of spintronic devices for future applications with low power consumption and high speed, a recent focus of such contact measurements has been magnetic systems, e.g., spin-valve behavior has been observed in single magnetic molecules or atoms on surfaces 8,9 and the occurrence of the Kondo effect has been found in ferromagnetic atomic contacts.…”

Section: Introductionmentioning

confidence: 99%

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Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study

et al. 2012

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We present a first-principles computational scheme for investigating the ballistic transport properties of onedimensional nanostructures with noncollinear magnetic order. The electronic structure is obtained within density functional theory as implemented in the full-potential linearized augmented plane-wave method and mapped to a tight-binding-like transport Hamiltonian via noncollinear Wannier functions. The conductance is then computed based on the Landauer formula using the Green's function method. As a first application, we study the conductance between two ferromagnetic Co monowires terminated by single Mn apex atoms as a function of Mn-Mn separation. We vary the Mn-Mn separation from the contact (about 2.5 to 5Å) to the far tunneling regime (5 to 10Å). The magnetization direction of the Co electrodes is chosen either in parallel or antiparallel alignment and we allow for different spin configurations of the two Mn spins. In the tunneling and into the contact regime, the conductance is dominated by s-d z 2 states. In the close contact regime (below 3.5Å), there is an additional contribution for a parallel magnetization alignment from the d xz and d yz states which give rise to an increase of the magnetoresistance as it is absent for antiparallel magnetization. If we allow the Mn spins to relax, a noncollinear spin state is formed close to contact due to the competition of ferromagnetic coupling between Mn and Co and antiferromagnetic coupling between the Mn spins. We demonstrate that the transition from a collinear to such a noncollinear spin structure as the two Mn atoms approach leaves a characteristic dip in the distance-dependent conductance and magnetoresistance of the junction. We explain this modification of the spin-valve effect due to the noncollinear spin state based on the spin-dependent hybridization between the d xz,yz states of the Mn spins and their coupling to the Co electrodes.

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Section: The Comentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study

et al. 2012

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“…Usually, a splitting of these maxima would have been expected because of the so--called ballistic magnetoresistance (BMR) [64,65], where the number of fully transmitted conductance channels changes upon applying a magnetic field. In particular, lifting the spin degeneracy modifies the number of modes for spin-up and spin-down subbands, which manifests itself in a magnetic field dependent opening and closing of discrete conductance channels of the contact leading to discrete conductance steps in the order of e 2 /h [66,67]. Surprisingly, these preferred conductance values did not change noticeably when a magnetic field (B = 5 T) was applied during opening and closing the contact and no preferred conductance at half-integer values of G 0 are observed.…”

Section: Ferromagnetic (Co) Single-atom Contactsmentioning

confidence: 99%

Electron Transport in Magnetic Quantum Point Contacts

et al. 2012

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In recent years, the fabrication of novel building blocks for quantum computation-and spintronics devices gained significant attention. The ultimate goal in terms of miniaturization is the creation of single-atom functional elements. Practically, quantum point contacts are frequently used as model systems to study the fundamental electronic transport properties of such mesoscopic systems. A quantum point contact is characterised by a narrow constriction coupling two larger electron reservoirs. In the absence of a magnetic field, the conductance of these quantum point contacts is quantised in multiples of 2e 2 /h, the so-called conductance quantum (G 0 ). However, in the presence of magnetic fields the increased spin-degeneracy often gives rise to a deviation from the idealized behaviour and therefore leads to a change in the characteristic conductance of the quantum point contact. Herein, we illustrate the complex magnetotransport characteristics in quantum point contacts and magnetic heterojunctions. The theoretical framework and experimental concepts are discussed briefly together with the experimental results as well as potential applications.

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“…With the possibility to perform transport measurements on nanoscale down to atomic-scale junctions using mechanically controllable break junctions 1 or scanning tunneling microscopy, [2][3][4][5][6][7] various fundamental questions on electron transport as well as practical problems concerning device functionality have arisen. With shrinking system size, the junctions have become considerably smaller than the mean-free path of a transmitted electron, reaching the ballistic transport regime.…”

Section: Introductionmentioning

confidence: 99%

One-dimensional ballistic transport with FLAPW Wannier functions

et al. 2012

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We present an implementation of the ballistic Landauer-Büttiker transport scheme in one-dimensional systems based on density functional theory calculations within the full-potential linearized augmented plane-wave (FLAPW) method. In order to calculate the conductance within the Green's function method, we map the electronic structure from the extended states of the FLAPW calculation to Wannier functions, which constitute a minimal localized basis set. Our approach benefits from the high accuracy of the underlying FLAPW calculations, allowing us to address the complex interplay of structure, magnetism, and spin-orbit coupling and is ideally suited to study spin-dependent electronic transport in one-dimensional magnetic nanostructures. To illustrate our approach, we study ballistic electron transport in nonmagnetic Pt monowires with a single stretched bond including spin-orbit coupling, and in ferromagnetic Co monowires with different collinear magnetic alignment of the electrodes with the purpose of analyzing the magnetoresistance when going from tunneling to the contact regime. We further investigate spin-orbit scattering due to an impurity atom. We consider two configurations: a Co atom in a Pt monowire and vice versa. In both cases, the spin-orbit induced band mixing leads to a change of the conductance upon switching the magnetization direction from along the chain axis to perpendicular to it. The main contribution stems from ballistic spin scattering for the magnetic Co impurity in the nonmagnetic Pt monowire, and for the Pt scatterer in the magnetic Co monowire from the band formed from states with d xy and d x 2 −y 2 orbital symmetry. We quantify this effect by calculating the ballistic anisotropic magnetoresistance, which displays values up to as much as 7% for ballistic spin scattering and gigantic values of around 100% for the Pt impurity in the Co wire. In addition, we show that the presence of a scatterer can reduce as well as increase the ballistic anisotropic magnetoresistance.

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The quantum spin-valve in cobalt atomic point contacts

Cited by 76 publications

References 36 publications

Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study

Conductance fingerprints of noncollinear magnetic states in single-atom contacts: A first-principles Wannier-functions study

Electron Transport in Magnetic Quantum Point Contacts

One-dimensional ballistic transport with FLAPW Wannier functions

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