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Special Issue "Ferromagnetic Semiconductors"

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

Deadline for manuscript submissions: closed (31 March 2010)

Special Issue Editor

Guest Editor
Prof. Dr. Wolfgang Nolting

Humboldt-University at Berlin, Institute of Physics / Chair: Solid State Theory, Newtonstr. 15, D-12489 Berlin, Germany
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Special Issue Information

Dear Colleagues,

In the last few years diluted ferromagnetic semiconductors have experienced a dramatic upsurge of interest due to their very promising potential for technological applications, on the one hand, and being attractive from a fundamental physics point of view, on the other. These materials might be able to integrate data processing (semiconductor technique: electron charge) and storage (ferromagnetism technique: electron spin) on a single chip. The simultaneous exploitation of charge and spin is known as “spintronics”. Undoubtedly ferromagnetism in such semiconducting materials would open the door for exciting microelectronic device applications provided the following non-trivial boundary conditions were fulfilled: (1) The Curie temperature should clearly exceed room temperature, (2) the charge carriers should react sensitively on changes in the magnetic state, and (3) the material should retain its excellent semiconductor properties. The simultaneous achievement of these objectives has been in the last years and continues to be the main goal of intense experimental as well as theoretical research on (diluted) ferromagnetic semiconductors.
The classical ferromagnetic semiconductors EuO and EuS have been investigated for several decades and are considered as rather well understood. For application, however, they do not come into question because of too low transition temperatures and only poor semiconductor properties. On the other hand, however, they may help to work out the basic physics of ferromagnetic semiconductors. More promising for future applications are (III,V) semiconductors doped with magnetic ions such as the prototypical Mn-doped GaAs with Curie temperatures well above 100K. Both localized magnetic moments and itinerant charge carriers are provided by the magnetic ion. Since the quality of the samples and their magnetic properties seem to be closely connected material science of growth and defects plays an important role with respect to spintronics aspects of such materials.
From a basic theoretical point of view the interplay between electronic structure, exchange interaction and moment disorder with respect to electric, magnetic and transport properties must be understood. By proper modelling and reliable many-body evaluation of the decisive magnetic correlations as well as “ab initio” calculations of real materials one can hope to get a better understanding of the fundamental physics of the ferromagnetism that occurs in (diluted) ferromagnetic semiconductors and of the prerequisites necessary for getting sufficiently high Curie temperatures.

Prof. Dr. Wolfgang Nolting
Guest Editor

Keywords

  • ferromagnetic local-moment systems
  • carrier-induced ferromagnetism
  • magnetic polaron
  • disorder and magnetic stability
  • Curie temperature
  • super-exchange
  • spintronics
  • spin-dependent transport
  • electronic correlations
  • nanomagnetism

Published Papers (4 papers)

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Research

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Open AccessArticle Ti-doped ZnO Thin Films Prepared at Different Ambient Conditions: Electronic Structures and Magnetic Properties
Materials 2010, 3(6), 3642-3653; doi:10.3390/ma3063642
Received: 20 April 2010 / Revised: 27 May 2010 / Accepted: 3 June 2010 / Published: 9 June 2010
Cited by 8 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres.
[...] Read more.
We present a comprehensive study on Ti-doped ZnO thin films using X-ray Absorption Fine Structure (XAFS) spectroscopy. Ti K edge XAFS spectra were measured to study the electronic and chemical properties of Ti ions in the thin films grown under different ambient atmospheres. A strong dependence of Ti speciation, composition, and local structures upon the ambient conditions was observed. The XAFS results suggest a major tetrahedral coordination and a 4+ valence state. The sample grown in a mixture of 80% Ar and 20% O2 shows a portion of precipitates with higher coordination. A large distortion was observed by the Ti substitution in the ZnO lattice. Interestingly, the film prepared in 80% Ar, 20% O2 shows the largest saturation magnetic moment of 0.827 ± 0.013 µB/Ti. Full article
(This article belongs to the Special Issue Ferromagnetic Semiconductors)

Review

Jump to: Research

Open AccessReview Mn-doped Ge and Si: A Review of the Experimental Status
Materials 2010, 3(12), 5054-5082; doi:10.3390/ma3125054
Received: 18 October 2010 / Revised: 16 November 2010 / Accepted: 19 November 2010 / Published: 26 November 2010
Cited by 11 | PDF Full-text (9827 KB) | HTML Full-text | XML Full-text
Abstract
Diluted ferromagnetic semiconductors (FMS) are in the focus of intense research due to their potential applications in spintronics and their striking new physical properties. So far Mn-doped III-V compound semiconductors such as GaMnAs are the most important and best understood ones, but they
[...] Read more.
Diluted ferromagnetic semiconductors (FMS) are in the focus of intense research due to their potential applications in spintronics and their striking new physical properties. So far Mn-doped III-V compound semiconductors such as GaMnAs are the most important and best understood ones, but they are ferromagnetic only at well below room temperature. An interesting alternative could be magnetic semiconductors based on elemental semiconductors, also owing to their compatibility with Si microelectronics. In the last decades, considerable amount of work has been devoted to fabricate Mn-doped Ge and Si FMS. In this article, the structural, magnetic and magneto-transport properties of Mn-doped Ge and Si will be reviewed. Full article
(This article belongs to the Special Issue Ferromagnetic Semiconductors)
Open AccessReview Carrier States in Ferromagnetic Semiconductors and Diluted Magnetic Semiconductors—Coherent Potential Approach—
Materials 2010, 3(6), 3740-3776; doi:10.3390/ma3063740
Received: 5 May 2010 / Accepted: 8 June 2010 / Published: 21 June 2010
Cited by 5 | PDF Full-text (1728 KB) | HTML Full-text | XML Full-text
Abstract
The theoretical study of magnetic semiconductors using the dynamical coherent potential approximation (dynamical CPA) is briefly reviewed. First, we give the results for ferromagnetic semiconductors (FMSs) such as EuO and EuS by applying the dynamical CPA to the s-f model. Next, applying
[...] Read more.
The theoretical study of magnetic semiconductors using the dynamical coherent potential approximation (dynamical CPA) is briefly reviewed. First, we give the results for ferromagnetic semiconductors (FMSs) such as EuO and EuS by applying the dynamical CPA to the s-f model. Next, applying the dynamical CPA to a simple model for A1−xMnxB-type diluted magnetic semiconductors (DMSs), we show the results for three typical cases to clarify the nature and properties of the carrier states in DMSs. On the basis of this model, we discuss the difference in the optical band edges between II-V DMSs and III-V-based DMSs, and show that two types of ferromagnetism can occur in DMSs when carriers are introduced. The carrier-induced ferromagnetism of Ga1−xMnxAs is ascribed to a double-exchange (DE)-like mechanism realized in the magnetic impurity band/or in the band tail. Full article
(This article belongs to the Special Issue Ferromagnetic Semiconductors)
Open AccessReview Element Specific Versus Integral Structural and Magnetic Properties of Co:ZnO and Gd:GaN Probed with Hard X-ray Absorption Spectroscopy
Materials 2010, 3(6), 3565-3613; doi:10.3390/ma3063565
Received: 1 April 2010 / Revised: 20 April 2010 / Accepted: 31 May 2010 / Published: 7 June 2010
Cited by 16 | PDF Full-text (3073 KB) | HTML Full-text | XML Full-text
Abstract
Dilute magnetic semiconductors (DMS) are envisioned as sources of spin-polarized carriers for future semiconductor devices which simultaneously utilize spin and charge of the carriers. The hope of discovering a DMS with ferromagnetic order up to room temperature still motivates research on suitable DMS
[...] Read more.
Dilute magnetic semiconductors (DMS) are envisioned as sources of spin-polarized carriers for future semiconductor devices which simultaneously utilize spin and charge of the carriers. The hope of discovering a DMS with ferromagnetic order up to room temperature still motivates research on suitable DMS materials. Two candidate wide-band gap DMS are Gd:GaN and Co:ZnO. We have used hard X-ray absorption spectroscopy (XAS) and in particular X-ray linear dichroism (XLD) and X-ray magnetic circular dichroism (XMCD) to study both DMS materials with element specificity and compare these findings with results from integral SQUID magnetometry as well as electron paramagnetic resonance (EPR). Full article
(This article belongs to the Special Issue Ferromagnetic Semiconductors)

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