903 research outputs found
Magnetic properties of Hydrogenated Li and Co doped ZnO nanoparticles
The effect of hydrogenation on magnetic properties of Zn0.85Co0.05Li0.10O
nanoparticles is presented. It was found that the sample hydrided at room
temperature (RT) showed weak ferromagnetism (FM) while that hydrided at 400oC
showed robust ferromagnetism at room temperature. In both cases reheating the
sample at 400oC in air converts it back into paramagnetic state (P) completely.
The characterization of samples by X-ray and electron diffraction (ED) showed
that room temperature ferromagnetism observed in the samples hydrogenated at RT
is intrinsic in nature whereas that observed in the samples hydrogenated at
400oC is partly due to the cobalt metal clusters.Comment: 10 pages, 3 figure
Room temperature Ferromagnetism in Th1-xFexO2-d (x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) nanoparticles
Nanocrystalline (Th1-xFex)O2-d particles with different Fe concentrations (x
= 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been prepared by a gel combustion
method. Rietveld refinement analyses of X-ray diffraction data revealed the
formation of an impurity free cubic type Th1-xFexO2-d structure up to x = 0.20.
This observation is further confirmed from the detailed studies conducted on 10
at. percent Fe doped ThO2 using high-resolution transmission electron
microscopy (HRTEM) imaging and indexing of the selected-area electron
diffraction (SAED) patterns. DC Magnetization studies as a function field
indicate that they are ferromagnetic with Curie temperature (Tc) well above
room temperature.Comment: 10 pages, 5 figure
Theory of Transition Temperature of Magnetic Double Perovskites
We formulate a theory of double perovskite coumpounds such as SrFeReO
and SrFeMoO which have attracted recent attention for their possible
uses as spin valves and sources of spin polarized electrons. We solve the
theory in the dynamical mean field approximation to find the magnetic
transition temperature . We find that is determined by a subtle
interplay between carrier density and the Fe-Mo/Re site energy difference, and
that the non-Fe same-sublattice hopping acts to reduce . Our results
suggest that presently existing materials do not optimize
Magnetic Behavior of Manganese-Doped ZnSe Quantum Dots
Magnetic properties of manganese-doped ZnSe quantum dots with the size of approximately 3.6 nm are investigated. The amount of Mn in the ZnSe quantum dots has been varied from 0.10% to 1.33%. The doping level in the quantum dots is much less than that used in the precursor. The co-ordination of Mn in the ZnSe lattice has been determined by electron paramagnetic resonance (EPR). Two different hyperfine couplings 67.3×10−4 and 60.9×10−4 cm−1 observed in the EPR spectrum imply that Mn atoms occupy two distinct sites; one uncoordinated (near the surface) and other having a cubic symmetric environment (nanocrystal core), respectively. Photoluminescence measurements also confirm the incorporation of Mn in ZnSe quantum dots. From the Curie-Weiss behavior of the susceptibility, the effective Mn-Mn antiferromagnetic exchange constant (J1) has been evaluated. The spin-glass behavior is observed in 1.33% Mn-doped ZnSe quantum dots, at low temperature. Magnetic behavior at a low temperature is discussed
Dynamical Mean Field Theory of Double Perovskite Ferrimagnets
The dynamical mean field method is used to analyze the magnetic transition
temperature and optical conductivity of a model for the ferrimagnetic double
perovskites such as . The calculated transition temperatures and
optical conductivities are found to depend sensitively on the band structure.
For parameters consistent with local spin density approximation band
calculations, the computed transition temperatures are lower than observed, and
in particular decrease dramatically as band filling is increased, in
contradiction to experiment. Band parameters which would increase the
transition temperature are identified.Comment: Supercedes cond-mat/000628 (PRB64 024424/1-4 (2001
Electronic structure study of double perovskites FeReO (A=Ba,Sr,Ca) and SrMoO (M=Cr,Mn,Fe,Co) by LSDA and LSDA+U
We have implemented a systematic LSDA and LSDA+U study of the double
perovskites FeReO (A=Ba,Sr,Ca) and SrMoO
(M=Cr,Mn,Fe,Co) for understanding of their intriguing electronic and magnetic
properties. The results suggest a ferrimagnetic (FiM) and half-metallic (HM)
state of FeReO (A=Ba,Sr) due to a pdd- coupling between the
down-spin Re/Fe orbitals via the intermediate O
ones, also a very similar FiM and HM state of SrFeMoO.
In contrast, a decreasing Fe component at Fermi level () in the
distorted CaFeReO partly accounts for its nonmetallic behavior,
while a finite - coupling between the down-spin
Re/Fe orbitals being present at serves to
stabilize its FiM state. For SrCrMoO compared with
SrFeMoO, the coupling between the down-spin Mo/Cr
orbitals decreases as a noticeable shift up of the Cr 3d
levels, which is likely responsible for the decreasing value and weak
conductivity. Moreover, the calculated level distributions indicate a
Mn(Co)/Mo ionic state in SrMnMoO
(SrCoMoO), in terms of which their antiferromagnetic insulating
ground state can be interpreted. While orbital population analyses show that
owing to strong intrinsic pd covalence effects, SrMoO
(M=Cr,Mn,Fe,Co) have nearly the same valence state combinations, as accounts
for the similar M-independent spectral features observed in them.Comment: 21 pages, 3 figures. to be published in Phys. Rev. B on 15th Se
The structural and magnetic properties of (In1-xFex)2O3 (0.0 <= x <= 0.25) system : prepared by gel combustion method
(In1-xFex)2O3 polycrystalline samples with x = (0.0, 0.05, 0.10, 0.15, 0.20
and 0.25) have been synthesized by a gel combustion method. Reitveld refinement
analysis of X raydiffraction data indicated the formation of single phase cubic
bixbyite structure without any parasitic phases. This observation is further
confirmed by high resolution transmission electron microscopy (HRTEM) imaging,
and indexing of the selected-area electron diffraction (SAED) patterns, X-ray
Absorption Spectroscopy (XAS) and Raman Spectroscopy. DC Magnetization studies
as a function of temperature and field indicatethat they are ferromagnetic with
Curie temperature (TC) well above room temperature.Comment: 9 pages 3 figure
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