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Magnetic Impurities (magnetic + impurity)

Distribution by Scientific Domains

Physics and Astronomy	83%

Selected Abstracts

Magnetic impurities in small metal clusters

ANNALEN DER PHYSIK, Issue 9-10 2005
G.M. Pastor
Abstract Magnetic impurities in small metallic clusters are investigated in the framework of the Anderson model by using exact diagonalization and geometry optimization methods. The singlet-triplet spin gap ,E shows a remarkable dependence as a function of band-filling, cluster structure, and impurity position that can be interpreted in terms of the environment-specific conduction-electron spectrum. The low-energy spin excitations involve similar energies as isomerizations. Interesting correlations between cluster structure and magnetic behavior are revealed. Finite-temperature properties such as specific heat, effective impurity moment, and magnetic susceptibility are calculated exactly in the canonical ensemble. A finite-size equivalent of the Kondo effect is identified and its structural dependence is discussed. [source]

Dilute Doping, Defects, and Ferromagnetism in Metal Oxide Systems

ADVANCED MATERIALS, Issue 29 2010
Satishchandra B. Ogale
Over the past decade intensive research efforts have been carried out by researchers around the globe on exploring the effects of dilute doping of magnetic impurities on the physical properties of functional non-magnetic metal oxides such as TiO2 and ZnO. This effort is aimed at inducing spin functionality (magnetism, spin polarization) and thereby novel magneto-transport and magneto-optic effects in such oxides. After an early excitement and in spite of some very promising results reported in the literature, this field of diluted magnetic semiconducting oxides (DMSO) has continued to be dogged by concerns regarding uniformity of dopant incorporation, the possibilities of secondary ferromagnetic phases, and contamination issues. The rather sensitive dependence of magnetism of the DMSO systems on growth methods and conditions has led to interesting questions regarding the specific role played by defects in the attendant phenomena. Indeed, it has also led to the rapid re-emergence of the field of defect ferromagnetism. Many theoretical studies have contributed to the analysis of diverse experimental observations in this field and in some cases to the predictions of new systems and scenarios. In this review an attempt is made to capture the scope and spirit of this effort highlighting the successes, concerns, and questions. [source]

Self-sustained current oscillations in a multi-quantum-well spin polarized structure with normal contacts

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2008
R. Escobedo
Abstract Self-sustained current oscillations (SSCO) are found in a nonlinear electron spin dynamics model of a n-doped dc voltage biased semiconductor II,VI multi-quantum well structure (MQWS) having one or more of its wells doped with Mn. Provided one well is doped with magnetic impurities, spin polarized current can be obtained even if normal contacts have been attached to this nanostructure. Under certain conditions, the system exhibits static electric field domains and stationary current or moving domains and time-dependent oscillatory current. We have found SSCO for nanostructures with four or more QWs. The presence of SSCO depends on the spin-splitting induced by both, the exchange interaction and the external magnetic field. We also calculate the minimal doping density needed to have SSCO, and a bound above which SSCO disappear. This range is crucial to design a device behaving as a spin polarized current oscillator. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Mixed singlet-triplet superconducting state in doped antiferromagnets

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2006
A. Maci¸ag
Abstract We analyze symmetry mixing in the superconducting (SC) order parameter of planar cuprates. The behavior of thermal conductivity observed in some systems doped with magnetic impurities or in some systems exposed to external magnetic field seems to indicate that such symmetry mixing takes place. We discuss this phenomenon in the framework of the spin polaron model (SPM). We assume that antiferromagnetic (AF) correlations, which are at least of short range, tend to confine motion of holes which have been created in the AF spin background. The nature of the propagation of quasiparticles which are hole-like and the nature of the interaction between quasiparticles is determined by a tendency to restore the local AF order. It is known that two holes in the t ,J model (tJ M) form bound states with dx 2,y2 or p-wave symmetry. The d-wave bound state has lower energy and is the ground state. The mixing of d-wave symmetry with p-wave symmetry takes place in the SC order parameter at some range of finite values of the doping parameter. That range lies at the applicability verge of the SPM, where AF correlation are already very short. On the other hand, these correlations may be strengthened by above mentioned external factors, which seems to explain why symmetry mixing is observed in this case. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Nitrides as spintronic materials

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
Tomasz Dietl
Abstract A report on the progress in spintronics-related works involving group III nitrides is given, emphasizing contradictory opinions concerning the basic characteristics of these materials. The actual position of magnetic impurities in the GaN lattice as well as a possible role of magnetic precipitates is discussed. The question as to whether the hole introduced by Mn impurities is localized tightly on the Mn d levels or rather on the hybridized p,d bonding states is addressed. The nature of spin,spin interactions and magnetic phases, as provided by theoretical and experimental findings, is outlined and the possible origins of the high-temperature ferromagnetism observed in (Ga, Mn)N are presented. Experimental studies aimed at evaluating characteristic times of spin coherence and dephasing in GaN are described. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]