共查询到20条相似文献,搜索用时 46 毫秒
1.
H.-F. Li Y. Su Y. G. Xiao J. Persson P. Meuffels Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):149-157
A neutron powder diffraction (NPD) study on the crystal and magnetic structure of a crushed La1-xSrxMnO3 (x ≈ 1/8) single crystal has been performed. The sample belongs to orthorhombic (Pnma, O) above the Jahn-Teller (JT) transition temperature (TJT) and monoclinic (P121/c1, M′) in the JT regime. We have also refined the NPD data below the charge/orbital ordering (CO/OO) temperature (TCO/OO) with a monoclinic (P121/c1, M′′) model because the experimental resolution was insufficient to clearly identify a triclinic structure. The refined lattice parameters show an obvious breathing-mode distortion between TCO/OO and TJT, accompanied by a large deviation of the monoclinic angle β from 90°, signifying a very strong cooperative JT distortion.
A ferromagnetic (FM) moment of 3.43(5)μ
B/Mn besides an A-type antiferromagnetic (A-AFM) moment of 0.54(2) μ
B/Mn is directed mainly along the b axis in P121/c1 symmetry at 5 K. With increasing temperature, the A-AFM domains transform into FM ones above ~100 K and the FM spin orientation
turns from the b to the c axis in crystallographic b-c plane below Tc = 187(1) K. The magnetization measurements show typical anomalies around TCO/OO and TJT. The measured saturation moment of 3.9(1)μ
B/Mn at 70 kOe and 5 K is well consistent with the sum 3.97(5)μ
B/Mn of the refined FM and A-AFM moments at 5 K, implying the A-AFM spins are aligned in field direction at 70 kOe. The applied
magnetic field can affect the paramagnetic insulating (PMI) state in the range of magnetic polarons. Based on the size of
JT distortion and the bond-valence sums (BVS’s), the CO/OO phenomenon is being discussed. 相似文献
2.
R. Bacewicz A. Twaróg T. Wojtowicz X. Liu 《Journal of Physics and Chemistry of Solids》2005,66(11):2004-2007
Local structure of Mn atoms in Ga1−xMnxAs epilayers was studied using the X-ray absorption fine structure (XAFS) at Mn K-edge. X-ray near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques were used. XAFS spectra for different Mn sites has been calculated and compared with the experimental data. Multi-parameter fitting of the EXAFS data indicates that 15-25% of Mn atoms are in interstitial sites in the as grown films. The Mn-As bond length has been found longer than Ga-As bond length in GaAs for both substitutional (MnGa) and interstitial (MnI) sites. 相似文献
3.
O. Toulemonde F. Studer A. Barnabé A. Maignan C. Martin B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):159-167
The XAS study at Cr, Co, Ni and Mn K-edges was performed for the doped CMR manganites Ln0.5Ca0.5Mn1-xBxO3 with Ln=La, Nd, Sm and B= Cr, Co, Ni (), on the samples that were studied previously for their ferromagnetic-metallic to antiferromagnetic-insulator transition.
We observed that the formal charges of the doping elements are Ni2+, Co2+ and Cr3+. It is also evidenced that the average formal charge of the manganese is increased after doping, in agreement with the charge
compensation keeping “O3” stoichiometry. These results suggest that the doping elements participate directly to the band structure.
Received: 9 January 1998 / Received in final form: 6 April 1998 / Accepted: 7 April 1998 相似文献
4.
Harishchandra Singh A.K. Sinha M.N. Singh P. Tiwari D.M. Phase S.K. Deb 《Journal of Physics and Chemistry of Solids》2014
X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Synchrotron X-ray diffraction (SXRD) techniques are used to study as synthesized and isochronally annealed samples of cobalt oxide nanoparticles (NPs) grown using the wet chemical route. Quantitative phase composition determined using Linear Combination Fitting (LCF) on XANES data is found to be in reasonably good agreement with that obtained from Rietveld refinement on SXRD data. XPS data qualitatively indicate that Co3O4 concentration increases with increase in the annealing temperature, in confirmation with SXRD and XANES data. Larger shifts in the satellite peaks from the main peaks compared to these in bulk suggest larger crystal field splitting in nanoparticles as compared to the bulk. 相似文献
5.
L. Bolotov N. Uchida T. Kanayama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):271-274
We present results of scanning tunneling spectroscopy (STS) measurements of hydrogen-saturated silicon clusters islands formed
on Si(111)-( 7×7) surfaces. Nanometer-size islands of Si6H12 with a height of 0.2-4 nm were assembled with a scanning tunneling microscope (STM) using a tip-to-sample voltage larger
than 3 V. STS spectra of Si6H12 cluster islands show characteristic peaks originating in resonance tunneling through discrete states of the clusters. The
peak positions change little with island height, while the peak width shows a tendency of narrowing for the tall islands.
The peak narrowing is interpreted as increase of lifetime of electron trapped at the cluster states. The lifetime was as short
as 10-13 s resulting from interaction with the dangling bonds of surface atoms, which prevents charge accumulation at the cluster
islands.
Received 30 November 2000 相似文献
6.
S. Sirbu T. Yamauchi Y. Ueda P. H.M. van Loosdrecht 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):289-296
Transport properties of the charge ordering compound
β-Na0.33V2O5 are studied in the temperature range from 30 K to 300 K using
current driven DC conductivity experiments. It is found that below
the metal-insulator transition temperature (
) this
material shows a nonlinear charge density modulation behavior. The
observed conductivity is discussed in terms of a classical domain
model for charge density modulation transport. 相似文献
7.
Equilibrium geometries, relative stabilities, and magnetic properties of small AunMn (n=1-8) clusters have been investigated using density functional theory at the PW91P86 level. It is found that Mn atoms in the ground state AunMn isomers tend to occupy the most highly coordinated position and the lowest energy structure of AunMn clusters with even n is similar to that of pure Aun+1 clusters, except for n=2. The substitution of Au atom in Aun+1 cluster by a Mn atom improves the stability of the host clusters. Maximum peaks are observed for AunMn clusters at n=2, 4 on the size dependence of second-order energy differences and fragmentation energies, implying that the two clusters possess relatively higher stability. The HOMO-LUMO energy gaps of the ground state AunMn clusters show a pronounced odd-even oscillation with the number of Au atoms, and the energy gap of Au2Mn cluster is the biggest among all the clusters. The magnetism calculations indicate that the total magnetic moment of AunMn cluster, which has a very large magnetic moment in comparison to the pure Aun+1 cluster, is mainly localized on Mn atom. 相似文献
8.
C. Bréchignac Ph. Cahuzac B. Concina J. Leygnier I. Tignères 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):185-192
The cross-sections for collisional charge transfer between singly charged free clusters M
n
+ (M = Li, Na; n=1...50) and atomic targets A (cesium, potassium) have been measured as a function of collisional relative velocity in laboratory
energy range 1–10 keV. For each cluster size, the experimental values of the charge transfer cross-section are fitted with an universal parametric curve with two independent parameters and vm, the maximum cross-section and the corresponding velocity. For small size clusters (), the characteristic parameters show strong variations with the number of atoms in the cluster. Abrupt dips observed for n=10 and n=22 are attributed to electronic properties. Charge transfer patterns observed for various collisional systems present similarities,
which appear more sensitive to cluster quantum size effects than to collision energy defects. In their whole, the and vm parameters show differences in both their size evolution and their absolute values discussed in term of projectile and target
electronic structures.
Received 13 April 2000 and Received in final form 29 June 2000 相似文献
9.
G. Pawłowski 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):471-479
The extended Hubbard model in the atomic limit (AL-EHM) on a square lattice with periodic boundary conditions is studied with
use of the Monte Carlo (MC) method. Within the grand canonical ensemble the phase and order-order boundaries for charge orderings
are obtained. The phase diagrams include three types of charge ordered phases and the nonordered phase. The system exhibits
very rich structure and shows unusual multicritical behavior.
In the limiting case of tij=0, the EHM is equivalent to the pseudospin model with single-ion anisotropy
, exchange interaction W in an effective magnetic field
. This classical spin model is analyzed using the MC method for the canonical ensemble. The phase diagram is compared with
the known results for the Blume-Capel model. 相似文献
10.
K. Pomorski K. Dietrich 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):353-364
We investigate the existence of stable charged metallic bubbles using the shell correction method. We find that for a given
mesoscopic system of n atoms of a given metal and (positive) elementary charges, a metallic bubble turns out to have a lower total energy than a compact spherical cluster,
whenever the charge number q is larger than a critical charge number qc. For a magic number (n-q) of free electrons, the spherical metallic bubble may become stable against fission.
Received: 17 November 1997 / Revised: 28 May 1998 / Accepted: 20 July 1998 相似文献
11.
H. Chang N.X. Chen J.K. Liang G.H. Rao 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):55-60
The structural stability of La2Co17-xMx (M = Mn, Mo, Nb, Ti, V, Al, Cr, Ni and Si) based on the interatomic potential has been studied. The calculated site preference
of the third element M is found to be the 6c site, which is in agreement with the experiments. In the calculations, if the
crystal cohesive energy of La2Co16Mn is taken as the highest one in the crystallization of La2Co17-xMx, the lowest content x of the third element M (M = Mn, Mo, Nb, Ti and V) required to stabilize La2Co17-xMx, is near that found in the experiments. The differences of the cell parameters between the calculated and the experimental
values are less than 0.4%. The differences of the atomic parameters for Co (or M) between the calculated and the experimental
values are about or even smaller than 1%, and that of La is about 3%. Because the energies of La(Co1-xAlx)13 are lower than those of La2(Co1-xAlx)17, La2(Co1-xAlx)17 could not be formed in the experiments. In the calculations, with either a range of deformation of the structure or the reconstruction
of the initial structure La2Co17 from LaCo5, the same results including the cohesive energy curves and the crystallographic parameters can be retrieved after the action
of the interatomic potentials.
Received 1st November 2002 / Received in final form 17 February 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: hchang@aphy.iphy.ac.cn 相似文献
12.
M. Tsuchiizu P. Donohue Y. Suzumura T. Giamarchi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):185-193
We investigate the physical properties of two coupled chains of electrons, with a nearly half-filled band, as a function of
the interchain hopping t
⊥ and the doping. We show that upon doping, the system undergoes a metal-insulator transition well described by a commensurate-incommensurate
transition. By using bosonization and renormalization we determine the full phase diagram of the system, and the physical
quantities such as the charge gap. In the commensurate phase two different regions, for which the interchain hopping is relevant
and irrelevant exist, leading to a confinement-deconfinement crossover in this phase. A minimum of the charge gap is observed
for values of t
⊥ close to this crossover. At large t
⊥ the region of the commensurate phase is enhanced, compared to a single chain. At the metal-insulator transition the Luttinger
parameter takes the universal value K
ρ
* = 1, in agreement with previous results on special limits of this model.
Received 31 July 2000 相似文献
13.
B. Huber M. Moseler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):485-489
We showed in a recent density functional study that small
palladium cluster on a MgO surface with F-centers can be oxidized
to epitaxial PdxOy nano-oxides below
room temperature [1].
Here, we employ density functional theory in order to explore
different methods for an experimental verification of the PdxOy
formation. The electronic density of states (DOS) of bare, O2-decorated and of oxidized palladium cluster was calculated.
For many cluster sizes a clear difference in the DOS could be observed allowing
for a detection of the oxidation with surface sensitive spectroscopic methods.
In addition, adsorption sites and stretch frequencies of a single CO molecule
on bare and oxidized Pd4 clusters were calculated.
While CO prefers hollow sites on Pd4, top
adsorption sites are found for Pd4O2. Markedly different CO stretch
frequencies indicate a possible discrimination of bare clusters and oxides
by Fourier transform infrared spectroscopy. 相似文献
14.
M.B. Zölfl Th. Maier Th. Pruschke J. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):47-53
We study one-particle spectra and the electronic band-structure of a CuO
2
-plane within the three-band Hubbard model. The Dynamical Mean-Field Theory (DMFT) is used to solve the many particle problem.
The calculations show that the optical gap is given by excitations from the lower Hubbard band into the so called Zhang-Rice singlet band. The optical gap turns out to be considerably smaller than the bare charge transfer energy () for a typical set of parameters, which is in agreement with experiment. We also investigate the dependence of the shape
of the Fermi surface on the different hopping parameters t
CuO and t
OO. A value t
OO
/
t
CuO
>0 leads to a Fermi surface surrounding the M point.
Received 21 September 1998 and Received in final form 8 June 1999 相似文献
15.
A.A. Guda N. Smolentsev J. Verbeeck Y. Zubavichus O.E. Polozhentsev 《Solid State Communications》2011,151(19):1314-1317
ZnO/ZnO:Mn core-shell nanowires were studied by means of X-ray absorption spectroscopy of the Mn K- and L2,3-edges and electron energy loss spectroscopy of the O K-edge. The combination of conventional X-ray and nanofocused electron spectroscopies together with advanced theoretical analysis turned out to be fruitful for the clear identification of the Mn phase in the volume of the core-shell structures. Theoretical simulations of spectra, performed using the full-potential linear augmented plane wave approach, confirm that the shell of the nanowires, grown by the pulsed laser deposition method, is a real dilute magnetic semiconductor with Mn2+ atoms at the Zn sites, while the core is pure ZnO. 相似文献
16.
A. Maignan C. Martin M. Hervieu B. Raveau 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):41-45
The substitution of manganese for cobalt in the perovskite La
0.8
Sr
0.2
CoO
3
has been studied. A significant increase of the magnetoresistance (MR) is obtained, reaching 60% at 5 K under 7 T for . This behavior originates from a spectacular increase of the resistivity correlated to a significant decrease of ferromagnetism
by Mn doping. This enhancement of magnetoresistance can be interpreted by the growth of ferromagnetic clusters in the insulating
matrix, by applying a magnetic field.
Received 7 May 1999 相似文献
17.
C. Tang K. Deng W. Tan Y. Yuan Y. Liu J. Yang X. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):125-128
The formation mechanism, geometric structures, and
electronic properties of a metal-substituted fullerene
C58Fe2 have been studied using frontier orbital theory
(FOT) and density functional theory (DFT). FOT predicts that two
Fe atoms prefer to substitute the two carbons of a [6,6] double
bond of C60 yielding a structure denoted as C58Fe2-3, which
is different from the two equivalent substitution sites, i.e., the
sites on the opposite of C60 cage or in the nearest
neighboring sites of a pentagonal ring for C58X2 (X=N and
B), and also different from the cross sites of a hexagonal ring
for C58Si2. Five possible structures of C58Fe2 are
optimized using DFT to see whether FOT works. The DFT calculations
support the prediction of FOT. The Mulliken charge of Fe atom in
C58Fe2-3 shows that the two Fe atoms of C58Fe2-3
lose 0.70 electron to the carbons of the cage, and the net spin
populations of Fe atom indicate that each Fe atom has 1.11 μB
magnetic moments, while each of the four nearest neighboring
carbons has
magnetic moments. Thus, the two Fe
atoms have ferromagnetic interaction with each other, and have
weak antiferromagnetic interaction with their four nearest
neighboring carbons, leaving 2.0 μB magnetic moments for the
molecule. 相似文献
18.
F. Nad' P. Monceau J.M. Fabre 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(3):301-306
Conductivity and permittivity of the organic transfer salt (TMTTF)2Br have been measured at low frequencies (102-107 Hz) between room temperature down to 4 K. The real part of the permittivity, , is shown to grow below the temperature at which the conductivity is maximum due to charge localization of Mott-Hubbard type. reaches a maximum of 105-106 at 35 K-50 K depending on the samples. Decreasing temperature below , sharply decreases down to helium temperature through the antiferromagnetic phase transition at T N = 15 K. We explain the magnitude, the temperature and frequency dependence of as resulting from short range charge density wave states in the temperature range where charge localization occurs. This
interpretation is supported by recent X-ray scattering measurements.
Received: 10 October 1997 / Revised: 28 February 1998 / Accepted: 3 March 1998 相似文献
19.
I. Popov T. Kunze S. Gemming G. Seifert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):439-446
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane
wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact.
It experiences a strong, mostly non-ionic attraction to the surface
at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between
adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room
temperature. The analysis of the electronic structure reveals a negligible
electron transfer and S-Au hybridised states, which indicate that the cluster-surface
interaction is dominated by S-Au bonds, with minor contributions from
the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters
on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox
active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within
nano-devices.
Therefore, a classical potential model was developed on the basis of the DFT data,
which allows to study larger cluster assemblies on the Au(111). 相似文献
20.
A. Paolone P. Roy A. Pimenov A. Loidl A.A. Mukhin A.M. Balbashov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):245-250
The optical conductivity of La0.85Sr0.15MnO3 single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies cm-1 and temperatures 10 K <
T
<300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La0.85Sr0.15MnO3 changes considerably below K revealing a structural phase transition induced by charge or orbital order. At T
=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity () in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the
polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with
a Drude-like behavior. The frequency and temperature dependence of in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).
Received 5 November 1999 相似文献