Scanning-tunneling-microscopy study of the growth of cobalt on Cu(111)

Figuera, Juan de la; Prieto, J. E.; Ocal, Carmen; Miranda, Rodolfo

doi:10.1103/physrevb.47.13043

Cited by 242 publications

(130 citation statements)

References 26 publications

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“…Therefore, the tip is magnetized along its axis leading to a magnetization perpendicular to the substrate surface [18]. Cobalt islands on Cu(111) are well studied [19,20,21] and identified as single-domain ferromagnetic exhibiting a perpendicular magnetization with strong coercivity and remanence [21]. Figure 1 shows a pseudo-three-dimensional scanning tunneling microscopy (STM) image of a Co island and single Co atoms adsorbed on Cu(111) at 7 K. The Co island exhibits a triangular shape and a thickness of two Co layers as expected.…”

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confidence: 99%

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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confidence: 99%

Quantized Conductance of a Single Magnetic Atom

Néel

Berndt

2009

Phys. Rev. Lett.

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“…The Cu(111) single crystal was cleaned in UHV by cycles of Ar ion sputtering and thermal annealing. Magnetic islands were obtained by depositing Co onto Cu(111) at room temperature (14)(15)(16). Fe and Cr atoms were deposited by e-beam evaporation while the sample was kept cold (~10K).…”

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Observing Spin Polarization of Individual Magnetic Adatoms

et al. 2007

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We have used spin-polarized scanning tunneling spectroscopy to observe the spinpolarization state of individual Fe and Cr atoms adsorbed onto Co nanoislands. Both of these magnetic adatoms exhibit stationary out-of-plane spin-polarization due to their direct exchange interaction with the substrate, but the sign of the exchange coupling between electron states of the adatom and the surface state of the Co island is opposite for the two: Fe adatoms exhibit parallel spin-polarization to the Co surface state while Cr adatoms exhibit antiparallel spin-polarization. First-principles calculations predict ferromagnetic and antiferromagnetic alignment of the spin moment for individual Fe and Cr adatoms on a Co film, respectively, implying negative spin-polarization for Fe and Cr adatoms over the energy range of the Co surface state.

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“…Segregation behavior is well documented in surfaceanalytical studies of Co on Cu single crystals of ͑100͒, ͑110͒, and ͑111͒ orientation. 25,26 VI. CONCLUSION We have interpreted the thickness-dependent conductance of NiO/Co/Cu/Co trilayer structures, measured in situ during deposition, in terms of intrinsic interface scattering.…”

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confidence: 99%

Electronic scattering from Co/Cu interfaces:In situmeasurement and comparison with theory

2000

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The full thickness-dependent electrical conductivity of polycrystalline NiO/Co/Cu/Co spin-valve structures was measured in situ during ion-beam deposition and compared with calculations based on realistic band structure. We have found striking features in the experimental conductivity which are unexpected from widely used semiclassical free-electron models. Addition of ϳ1 ML Co to a NiO/Co/Cu surface causes the net film conductance to decrease; the reverse case of Cu on NiO/Co shows a strong positive curvature of the thicknessdependent conductance, indicating a reduction of the conductivity in Cu near the interface with Co. Quantitative agreement is found between the experimental thickness-dependent film conductance and multiband tightbinding model calculations using a single constant parameter for on-site atomic disorder. The experimental data are consistent with strong scattering of conduction electrons in Cu at the interfaces with Co. Comparison with theory suggests that most of the observed interface scattering may be considered to be intrinsic, arising from the placement of a high density of empty Co d states at the Cu boundaries.

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Scanning-tunneling-microscopy study of the growth of cobalt on Cu(111)

Cited by 242 publications

References 26 publications

Quantized Conductance of a Single Magnetic Atom

Quantized Conductance of a Single Magnetic Atom

Observing Spin Polarization of Individual Magnetic Adatoms

Electronic scattering from Co/Cu interfaces:In situmeasurement and comparison with theory

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