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ABSTRACT: By means of first-principles calculations, we have investigated the effects of various
Li-doping on the exchange interaction and the formation energy in bulk GaN with Ga vacancies.
Although the Ga vacancies can induce ferromagnetism in GaN, their formation energy is rather
high. Our calculations show that Li-doping can effectively tune the formation energy of Ga
vacancies. It is revealed that the stabilizing effect depends on whether the number of holes is
increased or decreased after Li-doping. When Li atoms substitutes for N atoms or occupies the
interstitial sites, the holes are reduced and the formation energy of Ga vacancies is lowered.
In contrast, Li substituting for Ga generates additional holes in the system, leading to an
enhancement of the formation energy of Ga vacancies and making the system less stable.
EPL (Europhysics Letters) 01/2011; 93:57006. · 2.17 Impact Factor
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ABSTRACT: We present the structural and magnetic properties of Zn(0.95-x)Co(0.05)Al(x)O (x = 0.0 to 0.1) nanoparticles, synthesized by a novel sol-gel route followed by pyrolysis. Powder X-ray diffraction data confirms the formation of a single phase wurtzite type ZnO structure for all the compositions. The Zn(0.95)Co(0.05)O nanoparticles show diamagnetic behavior at room temperature. However, when Al is co-doped with Co with x = 0.0 to 0.10 in Zn(0.95-x)Co(0.05)Al(x)O, a systematic increase in ferromagnetic moment is observed up to x = 0.07 at 300 K. Above x = 0.07 (e.g. for x = 0.10) a drastic decrease in ferromagnetic nature is observed which is concomitant with the segregation of poorly crystalline Al rich ZnO phase as evidenced from TEM studies. Theoretical studies using density functional calculations on Zn(0.95-x)Co(0.05)Al(x)O suggest that the partial occupancy of S2 states leads to an increased double exchange interaction favoring the ferromagnetic ground states. Such ferromagnetic interactions are favorable beyond a threshold limit. At a high level doping of Al, the exchange splitting is reduced, which suppresses the ferromagnetic ordering.
Nanoscale 08/2010; 2(8):1505-11. · 5.91 Impact Factor
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ABSTRACT: Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by
powder x-ray diffraction, high resolution transmission electron microscopy, superconducting
quantum interference device magnetometry, and polarization measurements. Structural studies by
x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted
BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3.Alarge ferromagnetic hysteresis loop
is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is
observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties
are produced by the internal strain. Density functional calculations are used to substantiate the
results.
Applied Physics Letters 01/2010; 96:032903. · 3.84 Impact Factor
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ABSTRACT: We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study
its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All
calculations were performed using the projector augmented-wave method and generalized-gradient
approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at
1.1 μB per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms
varying from 3.25°A to 7.41°A. We conclude that the ferromagnetic phase in Fe-doped AlH3 is
stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due
to the holes created by Fe-doping and the larger level splitting of the interacting gap states within
the ferromagnetic phase.
EPL (Europhysics Letters) 01/2009; 85:67006. · 2.17 Impact Factor
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Epl. 94(1).
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ABSTRACT: Ba and Mn doped BiFeO(3) prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO(3) and a rhombohedral lattice for Mn substituted BiFeO(3). A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO(3). Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO(3), where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results.
Applied Physics Letters. 96(3).
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ABSTRACT: We have carried out a systematic theoretical investigation of Fe-doped AlH(3) to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 mu(B) per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 angstrom to 7.41 angstrom. We conclude that the ferromagnetic phase in Fe-doped AlH(3) is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase. Copyright (C) EPLA, 2009
Epl. 85(6).
