Ballistic magnetoresistance in transition-metal nanocontacts: The case of iron

Garcı́a, N.; Muñoz, Manuel; Zhao, Yibing

doi:10.1063/1.126416

Cited by 48 publications

(39 citation statements)

References 7 publications

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“…2 In the recent paper 16 18 If we use the experimental data of Ref. 17 for iron, δ(Fe) ≃ 0.59 − 0.65, then in our theory we obtain M R(Fe) = (100 − 140)%, which is larger than the experimentally measured 33%.…”

Section: (4)mentioning

confidence: 47%

“…17 for iron, δ(Fe) ≃ 0.59 − 0.65, then in our theory we obtain M R(Fe) = (100 − 140)%, which is larger than the experimentally measured 33%. 16 The justification of our model suggests that observed MR does not solely confined to a value of polarization δ. We believe that the basic condition for observation of upper MR limit, d w ≪ d s , is not fulfilled in the Fe-Fe PC experiment.…”

Section: (4)mentioning

confidence: 99%

“…In general case the angular integrals in (16) and (19) can be still evaluated analytically, whereas the integrations over k can be done only numerically. The results for the magnetoresistance (17) as function of the contact radius are shown on Fig.…”

Section: (4)mentioning

confidence: 99%

“…We believe that the basic condition for observation of upper MR limit, d w ≪ d s , is not fulfilled in the Fe-Fe PC experiment. 16 T 1 is proportional to the squared magnetic moment and the integral of exchange between conduction electrons and localized moments, and proportional to conduction electrons density of states at Fermi level. All these physical parameters for iron are larger than for cobalt, and especially than for nickel.…”

Section: (4)mentioning

confidence: 99%

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Ballistic versus diffusive magnetoresistance of a magnetic point contact

2001

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The quasiclassical theory of a nanosize point contacts (PC) between two ferromagnets is developed. The maximum available magnetoresistance values in PC are calculated for ballistic versus diffusive transport through the area of a contact. In the ballistic regime the magnetoresistance in excess of few hundreds percents is obtained for the iron-group ferromagnets. The necessary conditions for realization of so large magnetoresistance in PC, and the experimental results by García et al are discussed.PACS numbers: 74.80. Dm, 74.50.+r, In recent experiments on study of Ni-Ni and Co-Co point contacts (PC), a surprisingly high negative magnetoresistance exceeding 200% has been discovered. 1,2 The set up of the experiment was typical for observation of giant magnetoresistance (GMR), the effect observed earlier in hybrid systems involving ferromagnetic and normal multilayer metals. 3,4 However, for the multilayer structures the typical change of the resistance reached 10% − 30%, which is considerably lower than the corresponding values of Refs. 1,2. So, one can come easily to the conclusion that the main contribution to the MR comes from the region of the PC.A negative magnetoresistance can be due to scattering on domain walls (DW) and this effect has been considered in a number of works 5-8 giving typical values of MR in a range of few percents. Such considerably low values of the MR were obtained assuming that realistic widths of the DW were large, which resulted in a low scattering amplitudes. Considering sharp DW in the ballistic regime one comes to values ∼ 70%. 8 The fact that a sharp DW may give large MR was used in Ref. 2 to explain the anomalously large values of MR in the experiments on the point contacts. 1,2 However, the theory in Ref. 2 is the perturbation theory, it can not be applied to the explanation of 300% effect. The diminishing of the width of DW, when decreasing the size of the constriction was demonstrated by Bruno. 9 The DW width becomes comparable with PC length, and magnetization rotates almost abruptly inside the constriction. This conclusion holds until the diameter of PC is smaller than its actual length. With further increase of constriction size (diameter) the wall will bend outside of PC, and simple energy considerations show that the DW width will be of the order of PC size. 10

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Section: (4)mentioning

confidence: 47%

Section: (4)mentioning

confidence: 99%

Section: (4)mentioning

confidence: 99%

Section: (4)mentioning

confidence: 99%

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Ballistic versus diffusive magnetoresistance of a magnetic point contact

2001

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“…20,21,22,23,24,25 SDT measurements have also been carried out on Fe atomic contacts and magnetoresistances an order of magnitude smaller than for the Ni and Co systems were found. 26 This difference was explained in terms of the smaller ratio between the spin up and spin down densities of states at the Fermi level in bulk Fe than in Ni or Co. 26 Very recently, a theoretical study elucidating the systematics of SDT through a variety of nanocontacts, including Fe nanocontacts connected by atomic chains, has been reported. 16 The calculations were based on a semiempirical tight-binding model and were carried out in the limiting case of infinitesimal applied bias voltage.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of spin-dependent electron transport in atomic Fe nanocontacts

Dalgleish

Kirczenow

2005

Phys. Rev. B

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We present theoretical predictions of spintronic transport phenomena that should be observable in ferromagnetic Fe nanocontacts bridged by chains of Fe atoms. We develop appropriate model Hamiltonians based on semi-empirical considerations and the known electronic structure of bulk Fe derived from ab initio density functional calculations. Our model is shown to provide a satisfactory description of the surface properties of Fe nano-clusters as well as bulk properties. LippmannSchwinger and Green's function techniques are used together with Landauer theory to predict the current, magneto-resistance, and spin polarization of the current in Fe nanocontacts bridged by atomic chains under applied bias. Unusual device characteristics are predicted including negative magneto-resistance and spin polarization of the current, as well as spin polarization of the current for anti-parallel magnetization of the Fe nanocontacts under moderate applied bias. We explore the effects that stretching the atomic chain has on the magneto-resistance and spin polarization and predict a cross-over regime in which the spin polarization of the current for parallel magnetization of the contacts switches from negative to positive. We find resonant transmission due to dangling bond formation on tip atoms as the chain is stretched through its breaking point to play an important role in spin-dependent transport in this regime. The physical mechanisms underlying the predicted phenomena are discussed.PACS numbers: 75.47.-m,73.63.-b,72.25.-b,72.10.-d

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Geometry‐driven Magnetoresistance

Solin

Ram‐Mohan

2007

Handbook of Magnetism and Advanced Magnetic Materials

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Magnetoresistance (MR) in materials arises from two properties of the system. One is the physical MR that is dependent on the intrinsic properties of the materials in the physical system. The second source originates in the geometric structure and distribution of the materials in the physical system. In this review, we focus on the geometric MR and show how it can be altered and dramatically enhanced in two cases. First, in metal–semiconductor hybrid (MSH) structures, the judicious distribution of metal and semiconductor leads to a dramatic increase in the MR due to the rerouting of the current passing preferentially through the metallic regions at low fields, due to their high conductivity, into the semiconductor regions in the presence of a magnetic field. This phenomenon is now known as extraordinary magnetoresistance (EMR), with observed room‐temperature EMR in excess of 100% at 0.05 T and reaching values of 10 6 % at 5 T. This property of the MSH has been shown to be scalable down to structure dimensions on the order of ∼50 nm with a measured EMR of 35% at a signal field of 0.05 T. The details of the diffusive transport mechanism leading to the enhancements in MR are presented. Second, in nanocontacts between ferromagnetic wires, the quantum point contact leads to a ballistic magnetoresistance (BMR) that is due to the development of a domain wall (DW) between the wires when they are magnetized in an antiparallel configuration. The scattering of electrons by the DW in the nanochannels between the wires changes the conductance of the channel, and BMR of ∼300–3000% and higher have been observed. Here again the geometric origin of the MR is evident. The various aspects of the nanochannel governing BMR are discussed. Both geometric enhancements show great promise for technological applications in the area of reliable nanoscale sensors for computer read heads, magnetic actuators and switches, and biological sensors.

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Ballistic magnetoresistance in transition-metal nanocontacts: The case of iron

Cited by 48 publications

References 7 publications

Ballistic versus diffusive magnetoresistance of a magnetic point contact

Ballistic versus diffusive magnetoresistance of a magnetic point contact

Theoretical study of spin-dependent electron transport in atomic Fe nanocontacts

Geometry‐driven Magnetoresistance

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