共查询到20条相似文献,搜索用时 15 毫秒
1.
Guang-Dong Li Hui Wang Xiao-Ming Tan 《Journal of Physics and Chemistry of Solids》2006,67(11):2322-2325
By diagonalizing a set of complete energy matrices constructed for a d5 configuration ion in a trigonal ligand field, a reasonable interpretation is obtained for the EPR zero-field splitting of Mn2+ ions located at octahedral sites in yttrium aluminum garnet. It is shown that the local lattice structure around an octahedrally coordinated Mn2+ center has an expansion distortion, which may be attributed to the fact that the radius of Mn2+ ion is larger than that of Al3+ ion, and the Mn2+ ion will push the oxygen ligands outwards. Simultaneously, the local lattice structure distortion parameters ΔR=0.1825-0.2158 A and Δθ=1.220°-1.315° for the octahedral Mn2+ center in the crystal are determined, respectively. Meanwhile, we also demonstrated that the empirical impurity-ligand distance is not suitable for the YAG:Mn2+ system which has been approximately taken in previous works. 相似文献
2.
On the basis of the 120×120 complete energy matrices for a d3 configuration ion in a trigonal ligand field, for Cr3+ ions doped in MgTiO3 and LiTaO3, the local structures and EPR g factors of the octahedral (CrO6)9− clusters have been studied, respectively. By simulating the calculated optical spectra and the EPR spectra data to the experimental results, local structure parameters are obtained. The calculated results show that although the local lattice structures around the M (M=Mg2+, Ta5+) ions are obviously different, after Cr3+ replacing the M, the local lattice structures around the Cr3+ ions are quite similar and close to those of the Cr2O3. This may be ascribed to the fact that the octahedral Cr3+ center in MgTiO3:Cr3+ and LiTaO3:Cr3+ systems and that in Cr2O3 exhibit similar octahedral (CrO6)9− clusters. Moreover, the corresponding theoretical values of the optical spectra have been reported. It is also found that the orbital reduction factor k is very important to understand the EPR g factors for Cr3+ ions doped in MgTiO3 and LiTaO3. 相似文献
3.
4.
F. A. Bischoff O. Hübner W. Klopper L. Schnelzer B. Pilawa M. Horvatić C. Berthier 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):229-235
The quadrupole splitting in the 23Na nuclear magnetic resonance (NMR)
spectrum of the hexanuclear ferric wheel
Na@Fe6(tea)6
+ has been computed via an evaluation of the electric-field gradient (EFG) at the Na nucleus in the
framework of density-functional theory (DFT). The simulated spectrum is compared with experimental data.
A total of 26 = 64 Kohn-Sham determinants (a number that reduces to eight symmetry-unique determinants due to the
high S6 symmetry of the ferric wheel) with six localised high-spin Fe(III) centres (S = 5/2) could be
optimised in a self-consistent manner, and the corresponding DFT energies of all of these (broken-symmetry)
determinants coincide almost perfectly according to the Ising Hamiltonian solutions, especially when the energy
is computed from the B3LYP functional. The EFG at the Na atom
does not depend much on the specific Kohn-Sham determinant but depends on the
geometry of the ferric wheel and on the basis set used in the DFT calculations (particularly with regard to the atomic functions
on the Na atom). 相似文献
5.
M. Rotter M. Loewenhaupt S. Kramp T. Reif N.M. Pyka W. Schmidt R. van de Kamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):29-42
The magnetic excitations in the field induced ferromagnetic phase F3 of a NdCu2 single crystal were investigated by means of inelastic neutron scattering experiments. A mean field model using the random
phase approximation in connection with anisotropic magnetic bilinear R-R (R denotes a rare earth) exchange interactions is
proposed to account for the observed dispersion. The relevance of this model to the analysis of the magnetic ordering process
in other RCu2 compounds is discussed.
Received 21 April 1999 相似文献
6.
Z.-Y. Jiao X.-Y. Kuang X.-F. Huang J.-H. Li M.-L. Duan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):297-300
The complete energy matrices
for a d5configuration ion in a tetragonal
ligand-field has been constructed on the basis of the complete set of
basis
of d5configuration (252
dimension), and the relationship between the low-symmetry EPR parameters
b2
0 ,b4
0 and the local distortion parameters has been
established based on the complete energy matrices. As an application, we
have studied the EPR parameters and the local lattice structure of Mn2+
ion doped in tetragonal K2ZnF4 system. The calculation indicated that the local lattice structure around a tetragonal Mn2+ ion center has an expansion distortion. Simultaneously, the local lattice structure parameters R1 =2.0727 ?, R2 =2.0801 ? at room temperature (295 K) and R1
′ = 2.0439 ?, R2
′ =2.05478 ? at low
temperature (4.2 K) are determined. 相似文献
7.
Two sets of crystal field (CF) parameters have been proposed for DyFe2Si2, none of which could provide a simultaneous explanation of the available experimental data, particularly at low temperatures (below 100 K). The set derived from magnetic studies could not even explain the thermal variation of the magnetic specific heat reported in the same work. Although the set of CF parameters, obtained from a fit to the Mossbauer spectra, could provide a fairly good explanation of the thermal variation of the magnetic susceptibilities along the c-axis, it could not explain the observed thermal variation of other reported experimental findings. In the present work, an appraisal of the CF parameters proposed earlier has been done and a set of CF parameters has been derived, which provide a simultaneous explanation of all the available experimental data. The effect of substitution of Ge for Si on the magnetic properties and the magnetic specific heat of DyFe2Si2 has been studied in the framework of one electron crystal field model. The inelastic neutron scattering studies and EPR measurements are required to check the predicted Stark energies and the paramagnetic resonance g-values. 相似文献
8.
M. G. Brik 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):269-274
Systematic first-principles analysis of the energy level schemes and ground
state absorption spectra of trivalent chromium in ZnAl2S4 and
ZnGa2O4 crystals has been performed in the present paper. The
recently developed first-principles approach to the analysis of the
absorption spectra of impurity ions in crystals based on the discrete
variational multi-electron (DV-ME) method [K. Ogasawara et al., Phys. Rev. B
64, 115413 (2001)] was used in the calculations. The method is based on the
numerical solution of the Dirac equation; no phenomenological parameters are
used in the calculations. As a result, complete energy level schemes of the
Cr3+ ion and its absorption spectra in both crystals were calculated,
assigned and compared with experimental data. By performing analysis of the
molecular orbital (MO) population, it was shown that the covalency of the
chemical bonds between the Cr3+ and S2- ions is more significant
than that one between the Cr3+ and O2- ions. 相似文献
9.
T. Maitra A. Taraphder A. N. Yaresko P. Fulde 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):433-439
Motivated by the recent experimental studies on layered ferromagnetic
metallic system GdI2 and its doped variant GdI2Hx we develop a model
to understand their ground state magnetic phase diagram. Based on first
principle electronic structure calculations we
write down a phenomenological model and solve it under certain approximations
to obtain the ground state energy. In the process we work out the phase
diagram of the correlated double exchange model on a triangular lattice
for the specific band structure at hand. 相似文献
10.
Correlation between Zero-Field Splitting and Site Distortions of Cr^3+ Ions in NH4Cl:Cr^3+ System: a Complete Energy Matrix Study
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A theoretical method for investigating the inter-relation between the electronic and molecular structures of 3d^3 configuration ions in a tetragonal ligand field is established on the basis of the 120 × 120 complete energy matrices. Using this method, the local structure parameters of two tetragonal Cr^3+ centers in the NH4 Cl:Cr^3+ system are determined, Furthermore, the relations between the molecular symmetry and the ligand field symmetry are discussed. 相似文献
11.
G. Riou S. Jandl M. Poirier V. Nekvasil M. Diviš P. Fournier R.L. Greene D.I. Zhigunov S.N. Barilo 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):179-182
We present an infrared crystal-field study of Pr2CuO4 single crystals and thin films. Excitations from the ground state multiplet 3H4 to the 3H5, 3H6, 3F2 and 3F3 excited multiplets are observed in both single crystals and thin films. A precise set of crystal-field parameters, that reproduces
the energy and the symmetry of the levels, is determined.
Received 25 April 2001 相似文献
12.
K. Araki T. Goto Y. Nemoto T. Yanagisawa B. Lüthi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(3):257-259
The temperature dependence of the elastic constants in
Tb3Ga5O12 was measured and analysed with a simple crystal
field model. The magneto-elastic coupling constants have been deduced from
this experiment. The coupling constant gΓ5, related to the
c44 mode, is anomalously large. These coupling constants are important
for the interpretation of the phonon Hall effect. 相似文献
13.
R.C. Santana R.O. Cunha K.D. Ferreira R. Calvo 《Journal of Physics and Chemistry of Solids》2007,68(4):586-593
We investigated the crystal growth, electron paramagnetic resonance (EPR) and optical absorption spectra of l-threonine doped with Cu2+. The quality, size and habit of the single crystals grown from aqueous solution by the slow solvent evaporation and by the cooling methods vary when the impurities are introduced during the growth process. The variations with the magnetic field orientation of the EPR spectra of single-crystal samples at room temperature and 9.77 GHz in three crystal planes (ab, bc and ac) show the presence of copper impurities in four symmetry-related sites of the unit cell. These spectra display well resolved hyperfine couplings of the of Cu2+ with the ICu= of the copper nuclei. Additional hyperfine splittings, well-resolved only for specific orientations of the magnetic field, indicate that the copper impurity ions in the interstitial sites have two N ligands with similar hyperfine couplings. The principal values of the g and ACu tensors calculated from the EPR data are g1=2.051(1), g2=2.062(2), g3=2.260(2), ACu,1=16.9(5)×10−4 cm−1, ACu,2=21.8(6)×10−4 cm−1, ACu,3=180.0(5)×10−4 cm−1. The principal directions corresponding to g3 and to ACu,3 are coincident within the experimental errors, reflecting the orientation of the bonding planes of the copper ions in the crystal. The values of the crystal field energies are evaluated from the optical absorption spectrum, and the crystal field and bonding parameters of the Cu impurities in the crystal are calculated and analyzed. The EPR and optical absorption results are discussed in terms of the crystal structure of l-threonine and the electronic structure of the Cu2+ ions, and compared with data reported for other systems. The effects of the impurities in the growth and habit of the crystals are also discussed. 相似文献
14.
T. Domański 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(1):49-56
The method of continuous canonical transformation is applied to the double exchange model with a purpose to eliminate the
interaction term responsible for non conservation of magnon number. Set of differential equations for the effective Hamiltonian
parameters is derived. Within the lowest order (approximate) solution we reproduce results of the standard (single step) canonical
transformation. Results of the selfconsistent numerical treatment are compared with the other known studies for this model. 相似文献
15.
E. V. Sampathkumaran I. Das R. Vijayaraghavan A. Hayashi Y. Ueda M. Ishikawa 《Zeitschrift für Physik B Condensed Matter》1993,92(2):191-194
The temperature dependence of the lattice constants of the alloys, RCu2Ge2 (R=Nd, Tb, Dy, Ho and Tm) shows the existence of a lattice strain due to the alignment of the 4f-electric quadrupole at low temperatures. This strain could be related to the deviation of the Néel temperatures (T
N
) from that predicted by de Gennes scaling, thereby indicating the role of the quadrupole on the magnetism. On the other hand, in PrCu2Ge2, for which the enhancement ofT
N
is the largest in thisR series, the lattice constants interestingly behave as if the 4f-quadrupole moment is almost quenched and the anomalous magnetism in this case is attributed to some degree of 4f-delocalisation. 相似文献
16.
M. Capone D. Feinberg M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(1):103-109
It is shown that the layered antiferromagnetic order in stoechiometric cannot be understood purely from electronic interactions. On the contrary, it mainly results from strong cooperative Jahn-Teller
deformation. Those involve a compression of the Mn-O octahedron along the c-axis (mode Q
3
< 0), while alternate Jahn-Teller deformations occur in the ab-plane (mode Q2). These deformations stabilize a certain type of orbital ordering. The resulting superexchange couplings are calculated by
exact diagonalization, taking into account both eg and t2g orbitals. The main result is that antiferromagnetic (ferromagnetic) coupling along the c-direction (ab-planes) can be understood only if the Jahn-Teller energy is much larger than the superexchange couplings, which is consistent
with experiments. This mechanism contrasts with that based on weak Jahn-Teller coupling which instead predicts elongation
along the c-axis (Q
3
> 0). The crucial role of the deformation anisotropy is also emphasized.
Received 24 January 2000 相似文献
17.
Grossular is one of six members of silicate Garnet group. Two samples GI and GII have been investigated concerning their luminescence thermally stimulated (TL). EPR and optical absorption and the measurements were carried out to find out whether or not same point defects are responsible for all three properties. Although X-rays diffraction analysis has shown that both GI and GII have practically the same crystal structure of a standard grossular crystal, they presented different behavior in many aspects. The TL glow curve shape, TL response to radiation dose, the effect of annealing at high temperatures before irradiation, the dependence of UV bleaching parameters on peak temperature, all of them differ going from GI to GII. The EPR signals around g=2.0 as well as at g=4.3 and 6.0 have much larger intensity in GI than in GII. Very high temperature (>800 °C) annealing causes large increase in the bulk background absorption in GI, however, only very little in GII. In the cases of EPR and optical absorption, the difference in their behavior can be attributed to Fe3+ ions; however, in the TL case one cannot and the cause was not found as yet. 相似文献
18.
M.D. Núnez-Regueiro E. Chappel G. Chouteau C. Delmas 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):37-41
We study the magnetic structure of layered Li1-xNi1+xO2 and propose a new scheme: the AF interaction between the excess Ni2+ in the Li layers and the Ni3+ ions in the Ni planes, gives rise to the formation of ferrimagnetic clusters, which control the physics of these systems.
The values of the different interactions are estimated from a mean field calculation in the high temperature limit. For the
small x samples studied here the method does not yield an accurate value of , but it is very sensitive to the intralayer interactions, allowing to conclude that they are ferromagnetic. The recent proposal
of a quantum spin-orbital liquid in this system is discussed and the comparison with Jahn-Teller distorted NaNiO2 is made.
Received 8 December 1999 相似文献
19.
A. D. Prokhorov M. T. Borowiec M. C. Pujol I. M. Krygin A. A. Prokhorov V. P. Dyakonov P. Aleshkevych T. Zayarnyuk H. Szymczak 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):389-395
The electron paramagnetic resonance (EPR) of Yb3+
ions in a KY(WO4)2 single crystal was investigated at T=4.2 K and
fixed frequency of 9.38 GHz. The resonance absorption observed on the lowest
Kramers doublet represents the complex superposition of three spectra,
corresponding to the ytterbium isotopes with different nuclear moments. The
EPR spectrum is characterized by a strong anisotropy of the g-factors. The
temperature dependence of the g-factors is shown to be caused by the strong
spin-orbital and orbital-lattice coupling. The resonance lines broaden with
increasing temperature due to the short spin-lattice relaxation times. 相似文献
20.
用光谱和EPR谱确定CsMgBr3:Ni2+的局域结构 总被引:4,自引:2,他引:4
本文采用半自洽场(semi-SCF)自由Ni2 的3d轨道波函数、点电荷—偶极子模型和Ni2 -6X-(X=F,Cl,Br,I)络合物的μ-κ-α模型,建立了结构参数与光谱、EPR谱之间的定量关系,利用完全对角化方法,由光谱和电子顺磁共振(EPR)谱,确定了CsMgBr3:Ni2 晶体在77K温度时的局域结构参数,统一解释了CsMgBr3:Ni2 晶体的局域结构、光谱和EPR谱。所得理论结果与实验值符合得很好。此外,还讨论了晶体局域结构发生畸变的原因。 相似文献