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Magnetic Ions (magnetic + ion)

Distribution by Scientific Domains
Physics and Astronomy77%
Chemistry22%

Selected Abstracts

Effects of dilution and disorder on magnetism in diluted spin systems

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
Guixin Tang
Abstract The influence of configurational disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the ferromagnetic stability of diluted magnetic semiconductors. The equation of motion of the magnon Green's function is decoupled by Tyablikov approximation. With supercell approach, the concentrations of magnetic ions are determined by the size of the supercell in which there is only one magnetic ion per supercell in our method. In order to distinguish the influence of dilution and disorder, there are two kinds of supercells being used: the diluted and ordered case and the diluted and disordered case. The configurational averaging of magnon Green function due to disorder is treated in the augmented space formalism. The random exchange integrals between two supercells are treated as a matrix. The obtained magnon spectral densities are used to calculate the temperature dependence of magnetization and Curie temperature. The results are shown as following: (i) dilution leads to increasing the averaged distance of two magnetic ions, further decreases the effective exchange integrals and is main reason to reduce Curie temperature; (ii) spatial position disorder of magnetic ions results in the dispersions of the exchange integrals between two supercells and slightly changes ferromagnetic transition temperature; (iii) the exponential damping of distance dependence obviously reduces Curie temperature and should be set carefully in any phenomenological model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Neutron powder diffraction study of the anion-deficient La0.70Sr0.30MnO3.00-, manganites

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009
S. V. Trukhanov
Abstract Using powder neutron diffraction method the magnetic structure of the anion-deficient La0.70Sr0.30MnO3.00-, (, = 0, 0.15; 0.20) solid solutions at different temperatures has been defined. It is established that the magnetic structure changes with oxygen vacancies concentration. For the investigated samples the structural phase transitions have not been detected. The obtained data confirm the conception of the magnetic phase state forming for the Sr-doped anion-deficient manganites. In according to this conception in case of orbital ordering absence the lowering of the coordination of the magnetic ion results to change of the indirect superexchange interactions Mn3+ -O-Mn3+ sign from positive to negative. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-ray birefringence and dichroism obtained from magnetic materials

JOURNAL OF SYNCHROTRON RADIATION, Issue 4 2001
S. W. Lovesey
In the past decade, synchrotron radiation has triggered a surge in studies of the polarization dependence of X-ray beams passing through non-isotropic materials. A vast range of experimental results concerning polarization-dependent absorption (dichroism) and dispersion (birefringence, for example) are available from materials which are either magnetic or exhibit preferred directions due to the local atomic environment. This article aims to bring together the diversity of modern experiments in this field with established methods of optical calculus, in a way that highlights the simplicity of the underlying physics. A useful framework is formed when observable quantities, in the X-ray case, are related to atomic variables of the sample material. Atomic descriptions of absorption spectra with various levels of complexity are considered, and some well documented sum-rules are encountered. The framework is the most general allowed within the electric dipole approximation. By way of illustration, dichroic X-ray absorption by two materials with highly anisotropic properties and magnetic ions with different valence shells are considered; namely, a 3d -transition ion in ferrous niobate, and a lanthanide ion in dysprosium borocarbide. Both materials display interesting magnetic properties that are challenging to interpret at an atomic level of detail, and it is shown how absorption experiments can contribute to resolving some issues. [source]

Dynamics of spin interactions in diluted magnetic semiconductor heterostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2007
*Article first published online: 19 DEC 200, D. R. Yakovlev
Abstract This paper gives an overview of the recent studies of spin dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. The spin dynamics is controlled by energy and spin transfer between systems of magnetic ions, lattice (phonon system) and free carriers. Spin,lattice relaxation time of the Mn spin system is a very strong function of the Mn content, it decreases by five orders of magnitude when the Mn content changes from 0.4 to 11%. Additionally this time can be tuned by the varying free carrier concentration and by the growth of heteromagnetic structures with inhomogeneous profile of Mn ions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of dilution and disorder on magnetism in diluted spin systems

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
Guixin Tang
Abstract The influence of configurational disorder on the magnetic properties of diluted Heisenberg spin systems is studied with regard to the ferromagnetic stability of diluted magnetic semiconductors. The equation of motion of the magnon Green's function is decoupled by Tyablikov approximation. With supercell approach, the concentrations of magnetic ions are determined by the size of the supercell in which there is only one magnetic ion per supercell in our method. In order to distinguish the influence of dilution and disorder, there are two kinds of supercells being used: the diluted and ordered case and the diluted and disordered case. The configurational averaging of magnon Green function due to disorder is treated in the augmented space formalism. The random exchange integrals between two supercells are treated as a matrix. The obtained magnon spectral densities are used to calculate the temperature dependence of magnetization and Curie temperature. The results are shown as following: (i) dilution leads to increasing the averaged distance of two magnetic ions, further decreases the effective exchange integrals and is main reason to reduce Curie temperature; (ii) spatial position disorder of magnetic ions results in the dispersions of the exchange integrals between two supercells and slightly changes ferromagnetic transition temperature; (iii) the exponential damping of distance dependence obviously reduces Curie temperature and should be set carefully in any phenomenological model. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Anisotropy dependent magnetization relaxation in (Cd,Mn)Te quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
M. Goryca
Abstract An optical study of magnetization relaxation is presented for p-doped quantum wells with magnetic ions. The magnetic anisotropy of the system is controlled by the heavy-light hole splitting, tuned by uniaxial strain. We show that a suppression of the magnetic anisotropy results in an enhancement of the observed relaxation rate by a factor of at least 20. This is explained by the fact that the decrease of the anisotropy results in the lowering of the energy barrier for the domain magnetization flip process. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Spin and energy transfer between magnetic ions and freecarriers in diluted-magnetic semiconductor heterostructures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
D.R. Yakovlev
Abstract In this paper we give a brief overview of our studies on dynamical processes in diluted-magnetic-semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te. Presence of free carriers is an important factor which determines the energy- and spin transfer in a coupled systems of magnetic ions, lattice (the phonon system) and carriers. We report also new data on dynamical response of magnetic ions interacting with photogenerated electron-hole plasma. (Zn,Mn)Se/(Zn,Be)Se structures with relatively high Mn content of 11% provide spin-lattice relaxation time of about 20 ns, which is considerably shorter then the characterictic times of nonequilibrium phonons ranging to 1 ,s. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic Properties of a Ni2+ Kagome System

CHEMPHYSCHEM, Issue 2 2007
J. N. Behera
Magnetic frustration: The diverse nature of interactions occurring within kagome structures arise due to the interplay between the frustrated kagome geometry and the integer spin moment of the magnetic ions (see figure showing spin densities). Distortion in the kagome plane leads to Dzyaloshinsky-Moriya (DM) interactions at low temperatures giving rise to partial magnetic polarization. [source]