Spin blockade in ferromagnetic nanocontacts

a b s t r a c tMagnetic impurities in solids cause manifold changes in their macroscopic properties, such as anomalous low temperature resistance due to Kondo screening, reduction of the superconducting transition temperature due to local suppression of the order parameter, they create magnetic signatures in semiconductors, and lead to inelastic spin excitations in tunnel junctions. In the present paper we review what has been learnt about these effects from a surface science approach. Placing the magnetic impurities at well defined adsorption sites on single crystal surfaces makes their effect on the host, as well as their own magnetic properties better accessible to experiments, and also better understandable since the atomic environment of the impurity is exactly known lending comparison with theory more direct. After an introduction we discuss X-ray magnetic circular dichroism measurements which are spatially averaging and therefore report on ensemble properties. One of the recent progresses achieved in surface science is the preparation of well defined ensembles, such as surfaces with only single adatoms, each of them in an identical atomic environment and with sufficient mutual distance to exclude interactions. Due to this approach we can now determine the electronic configuration of individual adatoms, their hybridization with the host, and quantify their spin and orbital moments, as well as the spin-orbit induced magnetocrystalline anisotropy, which can be orders of magnitude larger than thin film and bulk values. In the second part we review recent progress in revealing the magnetic properties of individual atoms with the scanning tunneling microscope (STM). With this technique the spatial extent of the Kondo screening cloud and of subgap excitations in the superconductor quasiparticle density of states became apparent. We outline the first pioneering experiments measuring transport through reversible atomic point contacts containing magnetic atoms and measurements using the subgap features caused in superconducting STM tips to detect the magnetism of individual atoms. We then describe experiments using inelastic spin excitation spectroscopy to pin down the magnetic ground state and anisotropy energy of magnetic impurities. We continue with spin-polarized STM experiments reporting magnetization curves of individual magnetic adatoms and finish by a description of the most recent spin-excitation experiments revealing the necessary anisotropy environment for a high spin impurity to display the Kondo effect.

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“…[101]. This observation is in accordance with a calculation finding fully lifted spin degeneracy for ferromagnetic ballistic contacts [102].…”

Section: Magnetism Of Individual Surface Adsorbed Atoms Probed By Stmsupporting

confidence: 80%

Magnetism of individual atoms adsorbed on surfaces

2009

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“…In contrast, a series of recent experiments on magnetic nanostructures, and particularly nanowires, revealed that the magnetoresistance in the presence of DWs can be as large as several hundreds [4,5] or even thousands [6,7] of percents. These observations have decisive consequences in so far as DWs are controllable efficiently by applying a magnetic field [8] and can also be steered by a spin-polarized electric current [9], meaning that the magnetoresistance of the structure containing DW is controllable via an electric field.The interpretation of the huge magnetoresistance of DWs observed in magnetic semiconductor (in the ballistic quantum regime) relies on the relative sharpness of DWs on the scale set by the wavelength of carriers (electrons or holes) [10,11,12,13,14]. In such a situation spin-dependent scattering of carriers from DWs is greatly enhanced.…”

mentioning

confidence: 99%

“…The interpretation of the huge magnetoresistance of DWs observed in magnetic semiconductor (in the ballistic quantum regime) relies on the relative sharpness of DWs on the scale set by the wavelength of carriers (electrons or holes) [10,11,12,13,14]. In such a situation spin-dependent scattering of carriers from DWs is greatly enhanced.…”

mentioning

confidence: 99%

Tunable Conductance of Magnetic Nanowires with Structured Domain Walls

Dugaev¹,

Berakdar

Barnaś

2006

Phys. Rev. Lett.

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We show that in a magnetic nanowire with double magnetic domain walls, quantum interferences result in spin-split quasistationary states localized mainly in between the domain walls. Spin-flipassisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g. upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomena is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain walls parameters are readily controllable and the predicted effect is hence exploitable in spintronic devices.PACS numbers: 75.60. Ch,75.70.Cn,75.75.+a The discovery of the giant magnetoresistance [1] and its rapid and diverse industrial utilizations sparked major efforts in understanding and exploiting spin-dependent transport phenomena. In particular, new perspectives of even broader importance are anticipated from combining semiconductor technology with nanoscale fabrication techniques to produce magnetic semiconducting materials and control precisely the spins of the carriers. At the heart of this new field that is now termed "semiconductor spintronics" [2] is the understanding of the transport properties of a magnetic domain wall (DW), which is a region of inhomogeneous magnetization in between two domains of homogeneous (different) magnetizations. Thick (or adiabatic) DWs occurring in bulk metallic ferromagnets have an extension much larger than the carriers Fermi wave length and are largely irrelevant for the resistance [3]. In contrast, a series of recent experiments on magnetic nanostructures, and particularly nanowires, revealed that the magnetoresistance in the presence of DWs can be as large as several hundreds [4,5] or even thousands [6,7] of percents. These observations have decisive consequences in so far as DWs are controllable efficiently by applying a magnetic field [8] and can also be steered by a spin-polarized electric current [9], meaning that the magnetoresistance of the structure containing DW is controllable via an electric field.The interpretation of the huge magnetoresistance of DWs observed in magnetic semiconductor (in the ballistic quantum regime) relies on the relative sharpness of DWs on the scale set by the wavelength of carriers (electrons or holes) [10,11,12,13,14]. In such a situation spin-dependent scattering of carriers from DWs is greatly enhanced. In this paper we predict the formation of spin quantum wells and the occurrence of a novel effect in magnetic semiconductor nanowires with double DWs: By pinning one of the DWs at a constriction, one can control the location of the second DW. The spin-dependent transmission and reflection of carriers waves from the first and the second DW and the quantum interference between these waves lead to the formation of spin-split quasistationary states and hence the double DWs act in effect as a penetrable "spin quantum well" (located in between the two DWs). Lifetimes and...

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“…Our consideration is valid for complex wave vectors (17) which allows for extending this method to systems with insulating layers. Also our consideration can be applied to systems with fi nite lateral dimensions like magnetic nanowires [12].…”

Section: Resultsmentioning

confidence: 99%