Conductance quantization in magnetic nanowires electrodeposited in nanopores

Elhoussine, F; Mátéfi‐Tempfli, Stefan; Encinas, Armando; Piraux, Luc

doi:10.1063/1.1503400

Cited by 75 publications

(58 citation statements)

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“…However, several claims have appeared of the observation of half-integer conductance quantization for both magnetic and nonmagnetic metals. [8][9][10][11][12][13] Some related results have already appeared earlier and have been discussed in Sec. 5.4 of Ref.…”

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Absence of magnetically induced fractional quantization in atomic contacts

et al. 2004

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Using the mechanically controlled break junction technique at low temperatures and under cryogenic vacuum conditions we have studied atomic contacts of several magnetic ͑Fe, Co, and Ni͒ and nonmagnetic ͑Pt͒ metals, which recently were claimed to show fractional conductance quantization. In the case of pure metals we see no quantization of the conductance nor half quantization, even when high magnetic fields are applied. On the other hand, features in the conductance similar to ͑fractional͒ quantization are observed when the contact is exposed to gas molecules. Furthermore, the absence of fractional quantization when the contact is bridged by H 2 indicates the current is never fully polarized for the metals studied here. Our results are in agreement with recent model calculations. DOI: 10.1103/PhysRevB.69.081401 PACS number͑s͒: 73.63.Rt, 75.75.ϩa When a metallic wire is stretched its conductance becomes smaller as a result of the decrease of its cross section. This process continues until the breaking of the wire, and just before this event takes place, the contact is formed by just one atom. In this way atomic-sized contacts between two metallic electrodes can be formed and studied. The instruments that have made these studies possible are the mechanically controllable break junctions and the scanning tunneling microscope. In both techniques the relative displacement of two electrodes is controlled with a resolution of a few picometers by the use of a piezoelectric element which allows us to monitor the formation and breaking of the contact between the two electrodes.Properties of such atomic-sized contacts have been extensively studied during the past decade 1 for many different metals both magnetic and nonmagnetic. The conductance of these contacts can be described by the Landauer formulawhere the summation is extended to all the available channels for the electrons traversing the contact, T i is a number between 0 and 1 for the transmission of the ith channel, and G 0 ϭ2e 2 /h the quantum of conductance ͑assuming degeneracy of spin͒ in terms of the electron charge e and Planck's constant h. In the case in which the degeneracy of spin would be removed the channels would have to be redefined for each spin and each of these would carry up to 1 2 G 0 . The number of channels available in a one-atom contact is determined by the valence of the metal, 2 and the transmission of each channel is influenced by other parameters such as the number of neighbors or the bond distance. 3,4 For special cases (s-type metals such as Au or Na͒, electronic transport through a single atom will be due to a single channel with a transmission close to unity, but this will not be true for other metals where all kinds of combinations of channels with different transmissions will add up to produce the total conductance of the atom. This is the case for transition metals with partial occupation of the d orbitals and therefore they are not expected to have a one-atom conductance of 1 2 G 0 or 1 G 0 for magnetic or nonmagnetic metals, r...

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confidence: 68%

“…[8][9][10][11][12][13] Moreover, if the effects reported for room temperatures were a result of the metals being magnetic these effects should be even be more pronounced at low temperatures. Since this is not the case we have looked for other explanations for the observed ͑fractional͒ quantum peaks.…”

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confidence: 99%

Absence of magnetically induced fractional quantization in atomic contacts

et al. 2004

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“…These conditions appear difficult to fulfill. Nevertheless, experimental observations of conductance quantization in units of G 0 /2 have repeatedly been reported [3,4,5,6,7,8]. These conductances were observed with [4,6] or without [3,5,7,8] external magnetic fields, for ferromagnetic [3,4,5,6,7] and non-magnetic electrodes [7,8].…”

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confidence: 82%

Quantized Conductance of a Single Magnetic Atom

Néel

Berndt

2009

Phys. Rev. Lett.

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A single Co atom adsorbed on Cu(111) or on ferromagnetic Co islands is contacted with nonmagnetic W or ferromagnetic Ni tips in a scanning tunneling microscope. When the Co atom bridges two non-magnetic electrodes conductances of 2 e 2 /h are found. With two ferromagnetic electrodes a conductance of e 2 /h is observed which may indicate fully spin-polarized transport.PACS numbers: 68.37. Ef,72.25.Ba,73.23.Ad,73.63.Rt The conductance of nanometer-sized contacts may be decomposed into contributions of transport eigenchannels according to G = G 0 n i=1 τ i , where G 0 = 2e 2 /h is the quantum of conductance (-e: electron charge, h: Planck's constant), and τ i is the transmission probability of the ith channel [1,2]. The factor 2 in the quantum of conductance is due to spin degeneracy. In contacts involving magnetic electrodes the spin degeneracy of transport channels may be lifted. Each spin-polarized channel then may contribute up to G 0 /2 to the total conductance.A quantized conductance of G 0 /2 is expected when a fully spin-polarized current is transmitted with a probability of 1 through a spin-polarized transport channel. These conditions appear difficult to fulfill. Nevertheless, experimental observations of conductance quantization in units of G 0 /2 have repeatedly been reported [3,4,5,6,7,8]. These conductances were observed with [4,6] or without [3,5,7,8] external magnetic fields, for ferromagnetic [3,4,5,6,7] and non-magnetic electrodes [7,8]. On the other hand, the absence of noninteger conductance quantization has also been inferred from experimental results [9,10]. Untiedt et al. showed that contaminants like H 2 or CO modify the conductance and could, in the case of CO adsorption on Pt electrodes, give rise to a conductance of G 0 /2 [10]. A considerable variety of model calculations [11,12,13,14,15] have been performed and support the notion that conductance quantization in units of G 0 /2 is not expected from the investigated ferromagnetic contacts. It should be noted, however, that the modeling performed so far did not include geometrical relaxations of the contacts although the importance of the detailed atomic arrangement has been emphasized [11,15,16,17].The contradictory conclusions reached from the various experiments may be related to a lack of characterisation of the atomic details of the junction. This problem may be reduced by using a cryogenic scanning tunneling microscope to probe the conductance of clean singleatom contacts in ultra-high vacuum. Here we apply this approach to investigate prototypical junctions. A single magnetic atom on a spin-polarized island or a nonmagnetic substrate is contacted with non-magnetic and ferromagnetic tips. We find that the conductance of a single Co atom is G 0 when two non-magnetic electrodes are used. With ferromagnetic electrodes the conductance is G 0 /2. Conductances of ≈ 0.9 G 0 are observed for a combination of a non-magnetic and a ferromagnetic electrode. In contrast to previous experiments, the contact geometry and chemistry are character...

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“…∆G = G 0 2 = e 2 h . Indeed, half-integer conductance quanta have been observed in both magnetic-and non-magnetic point contacts, particularly in external magnetic fields [43][44][45][46][47][48][49][50].…”

Section: Electron Transport Through Atomic-sized 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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Conductance quantization in magnetic nanowires electrodeposited in nanopores

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Cited by 75 publications

References 14 publications

Absence of magnetically induced fractional quantization in atomic contacts

Absence of magnetically induced fractional quantization in atomic contacts

Quantized Conductance of a Single Magnetic Atom

Electron Transport in Magnetic Quantum Point Contacts

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