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Special Issue "Spintronics"

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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 June 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Irene D'Amico

Information Centre, Market Square, Department of Physics, University of York, York YO10 5DD, UK
Website | E-Mail
Fax: +44 1904 322 214
Interests: spin transport; spin dynamics; spintronics; semiconductor quantum dots; quantum computation; density functional theory

Special Issue Information

Dear Colleagues,

Spintronics – or spin-electronics – is an emerging technology which aims to revolutionize traditional electronics by combining the well-known functionalities derived from the charge of carriers (usually electrons or “holes”) with the properties of their spin degrees of freedom. These can be exploited by engineering interactions between spins and electric or magnetic fields. Alternatively spin behaviour can be influenced by the environment offered by different materials, or by constraints due to the system geometry, or by its patterning with nano-structures.

‘Spintronics’ encompasses by now many different subfields and interlaces with spin-based quantum information. While valuable progress and discoveries have been made so far, important open questions remain, from optimizing spin injection in semiconductor device elements to improving understanding and control of spin dynamics and coherence. This special issue focuses on this mixture of prospective applications and open fundamental problems to provide exciting science and technology for many years to come.

Dr. Irene D'Amico
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed Open Access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs).

Keywords

  • spintronics
  • spin injection
  • spin transport
  • spin coherence
  • spin diffusion
  • spin galvanic effect
  • spin Seebeck effect
  • spin Coulomb drag
  • spin Hall effect
  • spin torque
  • magnetic domain walls
  • magnetic semiconductors
  • topological insulators
  • quantum information
  • magnetic nanoparticles
  • magnetic recording
  • magnetoresistance
  • spin orbit coupling

Published Papers (5 papers)

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Research

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Open AccessArticle Spin Relaxation in GaAs: Importance of Electron-Electron Interactions
Materials 2014, 7(4), 2795-2814; doi:10.3390/ma7042795
Received: 11 November 2013 / Revised: 14 March 2014 / Accepted: 26 March 2014 / Published: 9 April 2014
Cited by 2 | PDF Full-text (738 KB) | HTML Full-text | XML Full-text
Abstract
We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that
[...] Read more.
We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into account electron-electron interactions within the simulations, results for the spin relaxation time—with respect to both electron density and temperature—will reach good quantitative agreement with corresponding experimental data. Our calculations contain no fitting parameters. Full article
(This article belongs to the Special Issue Spintronics)
Figures

Open AccessArticle Topological Defects in Topological Insulators and Bound States at Topological Superconductor Vortices
Materials 2014, 7(3), 1652-1686; doi:10.3390/ma7031652
Received: 9 September 2013 / Revised: 10 February 2014 / Accepted: 11 February 2014 / Published: 4 March 2014
Cited by 4 | PDF Full-text (712 KB) | HTML Full-text | XML Full-text
Abstract
The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the
[...] Read more.
The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the topological defect can be described as a distortion of the metric in curved space, which can be accounted for by a rotation of the Gamma matrices and by a spin connection inherited with the curvature. These features modify the scattering properties of the carriers. We discuss the self-energy of defect formation with this approach and the electron cross-section for intra-valley scattering at an edge dislocation in graphene, including corrections coming from the local stress. The cross-section contribution to the resistivity, ρ, is derived within the Boltzmann theory of transport. On the same lines, we discuss the scattering of a screw dislocation in a two-band 3D TI, like Bi1-xSbx, and we present the analytical simplified form of the wavefunction for gapless helical states bound at the defect. When a 3D TI is sandwiched between two even-parity superconductors, Dirac boundary states acquire superconductive correlations by proximity. In the presence of a magnetic vortex piercing the heterostructure, two Majorana states are localized at the two interfaces and bound to the vortex core. They have a half integer total angular momentum each, to match with the unitary orbital angular momentum of the vortex charge. Full article
(This article belongs to the Special Issue Spintronics)
Open AccessArticle Room Temperature Ferromagnetic Mn:Ge(001)
Materials 2014, 7(1), 106-129; doi:10.3390/ma7010106
Received: 27 September 2013 / Revised: 16 December 2013 / Accepted: 16 December 2013 / Published: 27 December 2013
Cited by 2 | PDF Full-text (1272 KB) | HTML Full-text | XML Full-text
Abstract
We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high
[...] Read more.
We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed. Full article
(This article belongs to the Special Issue Spintronics)
Open AccessArticle Room-Temperature Electron Spin Generation by Femtosecond Laser Pulses in Colloidal CdS Quantum Dots
Materials 2013, 6(10), 4523-4531; doi:10.3390/ma6104523
Received: 7 August 2013 / Revised: 16 September 2013 / Accepted: 8 October 2013 / Published: 15 October 2013
Cited by 1 | PDF Full-text (211 KB) | HTML Full-text | XML Full-text
Abstract
We present an experimental investigation of optical spin orientation in colloidal CdS quantum dots (QDs) by a femtosecond laser pulse at room temperature. The spin carrier and its spin-generation process are clarified. Firstly, the observed spin signals of CdS QDs in time-resolved Faraday
[...] Read more.
We present an experimental investigation of optical spin orientation in colloidal CdS quantum dots (QDs) by a femtosecond laser pulse at room temperature. The spin carrier and its spin-generation process are clarified. Firstly, the observed spin signals of CdS QDs in time-resolved Faraday rotation measurements are shown to belong to electron carriers, by comparing the spin dephasing dynamics and Landé g factor between CdS QDs and bulk materials. Secondly, spin dynamics unaffected by the faster carrier recombination suggests that the spin-polarized electrons are not photoexcited but resident in the dots. Moreover, hole spins should dephase very fast compared with electron spins, otherwise the trion (two electrons with opposite spin orientations and one hole) recombination process will affect the resident electron spin signals. The electron spin is generated in a short time of which the excitation light is absorbed and the resident electron is excited to trion states, i.e., of pulse durations. Due to fast hole spin dephasing, trion recombination gives null spin signals, and the subsequent electron spin dynamics is controlled by its intrinsic mechanisms. Full article
(This article belongs to the Special Issue Spintronics)

Other

Jump to: Research

Open AccessLetter The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1−xSi Heusler Alloys
Materials 2014, 7(3), 1473-1482; doi:10.3390/ma7031473
Received: 2 December 2013 / Revised: 26 December 2013 / Accepted: 18 February 2014 / Published: 25 February 2014
Cited by 5 | PDF Full-text (505 KB) | HTML Full-text | XML Full-text
Abstract
In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS) alloys. The electronic calculations are based on density
[...] Read more.
In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co–Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5–0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures. Full article
(This article belongs to the Special Issue Spintronics)

Submitted Papers

Type of Paper: Article
Title: Topological defects in Topological Insulators and bound states at Topological Superconductor vortices
Authors: V. Parente1,2,3, G. Campagnano2, A. Tagliacozzo1,2 and F. Guinea3
Affiliations: 1 Università degli studi di Napoli “Federico II”, Napoli, Italy; 2 CNR-SPIN, Napoli, Italy; 3 Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, Spain
Abstract: Scattering of Dirac electrons by topological defects and bound states have been proposed as the most relevant source of resistance in graphene [1]  and  at the boundary surfaces of three dimensional  Topological Insulators (3D-TI).  Striking enough, when a 3D-TI is proximized by a superconductor, a vortex  can bind a Majorana fermionic quasiparticle at the interface [2].

We will discuss the electron cross section for intravalley scattering at an edge dislocation in graphene and its contribution to the resistivity r within the Boltzmann  theory  of transport, including corrections coming from the local stress.  The result will be compared to the resistivity induced by a localized gaussian bump [3], curving the surface. The long wavelength continuous limit will be used throughout. The unifying scheme of the Dirac equation on  a curved space[4,5] allows us to consider topological  point-like defects and bumps for an unrelaxed lattice, on the same foot.  While r is proportional to the carrier concentration n when electrons scatter  off a bump,  an edge dislocation  provides the expected  inverse dependence rµn-1 [6]. Smooth potentials are likely not to change the isospin and the valley of the scattering electrons, nor their energy spectrum drastically, unless the strain  produces gaps or zero energy states[7,8].

Next we present the solution for a bound state at a  screw disclination in a two band 3D-TI like Bi2Se3. When the TI is proximized by a superconductor and a vortex pierces  the TI, a bound state forms at the interfaces in the vortex core, which acts in analogy with the singularity of a screw disclination. If the parity of the order parameter of the superconductor is even, the bound state excitation is a Majorana bound state. This is not the case if the parity is odd [9].

References

[1] M. I. Katsnelson, F. Guinea  and A. K. Geim,  Phys.Rev. B 2009, 79, 195426.
[2] L. Fu and C.L. Kane, Phys. Rev. Lett. 2008, 100, 096407.
[3] V. Parente, P. Vitale, A. Tagliacozzo and  F. Guinea, unpublished.
[4] F. De Juan, A. Cortijo and M.A. Vozmediano, Phys. Rev. B 2007, 76, 165409.
[5] V. Parente, P. Lucignano,  P. Vitale, A. Tagliacozzo and  F. Guinea, Phys. Rev. B 2011, 83, 075424.
[6] F.Guinea, J. Low. Temp. Phys.2008, 153, 359.
[7] V.M. Pereira, A.H. Castro Neto, and N.M.R. Peres, Phys. Rev. B 2009, 80, 045401.
[8] F. Guinea, M. I. Katsnelson and A. K. Geim, Nat.Phys. 2010, 6, 30.
[9] A. Tagliacozzo, P. Lucignano and F. Tafuri, Phys. Rev. B 2012, 86, 045435.

Keywords: Dirac electrons; topological effects; two band topological insulators; Majorana bound state

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Type of Paper: Article
Title:
Atomic Ordering Effects in Highly Spin-Polarized Co-based Full Heusler Alloys
Authors: P.J. Hasnip, C. Loach, J.H. Smith, M.I.J. Probert and V.K. Lazarov
Affiliation: Department of Physics, University of York, York YO10 5DD, UK
Abstract: Co-based full Heusler alloys are predicted to be half-metallic in bulk, making them excellent candidates for spintronics devices such as current-perpendicular-to-plane spin valves. This half-metallicity has yet to be realised in device or thin film heterostructures, a discrepancy often attributed to the level of chemical and structural disorder in the thin films. Such disorder ultimately reduces the spin polarization of the Heusler alloys at the Fermi level, destroying their half-metallicity.

We present a first principles study of the effect of disorder on the spin polarization of the bulk Co-based Heusler alloys Co2MnSi, Co2FeSi and Co2MnxFe1-xSi. The half-metallicity is shown to be lost in the presence of most types of disorder, though in several cases the spin polarization at the Fermi level remains high. Whilst the spin polarization is lost or even reversed when intermixing occurs between the Co sublattice and the Fe/Mn or Si sublattices, the polarization is relatively robust when the Co sublattice is kept intact. Calculations of the disordering energies show that it is particularly favourable energetically to keep the Co sublattice intact, suggesting that high spin polarization may be recovered by suitable annealing. A comparison of the disordering energies across the various Co-based Heuslers provides insight into the ordering trend amongst these materials and the qualitative benefits of annealing at various temperatures. This latter insight is important in guiding the future growth and post-growth treatment of such Heusler-based heterostructures.

 

Type of Paper: Review
Title: Spin and Charge Excitations in Low Dimensional Electron Liquids
Author: Florent Perez
Affiliation: Institut des NanoSciences de Paris, Université Pierre et Marie Curie, Paris, France
Abstract: We review 15 years of optical exploration of low energy spin and charge excitations, like plasmons, spin-plasmons, spin-waves and individual excitations, of electron gases confined in semi-conductor quantum wells and wires. The electronic Raman scattering probe has, during these years, proven its efficiency in the accurate determination of the dispersion of these excitations. These explorations aimed at improving the understanding of the Coulomb interaction between confined electrons. Recently, the introduction of test-bed spin-polarized electron gases gave an experimental access to spin-resolved Coulomb interactions. Very recently, intriguing interplay between spin-orbit and Coulomb interactions has been discovered.
Keywords: spin-plasmon, plasmon, spin-wave, electron gas, quantum wells, Coulomb interaction, spin-orbit interaction, Raman scattering


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