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1.
Magnetism in Rh clusters under hydrostatic deformations 总被引:1,自引:0,他引:1
E.O. Berlanga-Ramırez F. Aguilera-Granja A. Dıaz-Ortiz A. Vega 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):343-349
The magnetic behavior of rhodium clusters RhN (N = 4-38) under hydrostatic deformations was investigated. The starting cluster structures were obtained from an evolutionary
search algorithm applied to a Gupta potential. The spin-polarized electronic structure and related magnetic properties were
calculated using a self-consistent spd tight-binding Hamiltonian within the unrestricted Hartree-Fock approximation. The magnetic behavior was analyzed in terms
of the interdependence between the geometrical parameters and the electronic structure. Anomalous magnetic effects were found
in some cases.
Received 5 August 2002 / Received in final form 10 January 2003 Published online 4 March 2003
RID="a"
ID="a"e-mail: berlanga@dec1.ifisica.uaslp.mx 相似文献
2.
F. Aguilera-Granja A. Vega J. Rogan W. Orellana G. García 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):125-131
We report a comparative study of the magnetic properties of
free-standing PdN clusters (2 ≤N ≤21) obtained
through two different theoretical approaches that are extensively
employed in electronic structure calculations: a semi-empirical
Tight-Binding (TB) model and an ab-initio DFT pseudopotential
model. Conclusions are drawn about the reliability of the TB model for
the investigation of the electronic structure and magnetic properties
of such complex 4d Transition Metals (TM) systems and we compare the
results with previous systematic DFT calculations and comment on some
available experiments in the literature. 相似文献
3.
A. Szytu?a ?. Gondek A. Arulraj B. Penc 《Journal of magnetism and magnetic materials》2009,321(20):3402-3405
Physical properties of NdAu2Ge2, crystallising with the tetragonal ThCr2Si2-type crystal structure, were investigated by means of magnetic, calorimetric and electrical transport measurements as well as by neutron diffraction. The compound exhibits antiferromagnetic ordering below TN=4.5 K with a collinear magnetic structure of the AFI-type. The neodymium magnetic moments are parallel to the c-axis and amount to 1.04(4) μB at 1.5 K. The observed magnetic behaviour is strongly influenced by crystalline electric field effect. 相似文献
4.
N. Fujima T. Oda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):89-92
Atomic structures and non-collinear magnetic moments are
calculated by the first principle molecular dynamics for
Fe5 and Fe6 linear
chains with several fixed and free chain-lengths. The
dimerization appears in the optimized atomic structures of all
the chains. For the Fe5, the magnetic
arrangement is parallel for a large chain-length and changes to
non-collinear with decreasing the chain-length. For the
Fe6, the magnetic arrangement is
antiparallel in a unit of dimer for a small chain-length and
changes to non-collinear with increasing the chain-length. These
magnetic behaviors are simulated by a simple
J1-J2 Heisenberg
model. 相似文献
5.
A. D. Rata H. Braak D. E. Bürgler S. Cramm C. M. Schneider 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):445-451
We investigate the structure and magneto-transport
properties of thin films of the Co2Cr0.6Fe0.4Al
full-Heusler compound, which is predicted to be a half-metal by
first-principles theoretical calculations. Thin films are deposited
by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized
Si substrates to highly textured and even epitaxial on MgO(001)
substrates, respectively. Our Heusler films are magnetically very
soft and ferromagnetic with Curie temperatures up to 630 K. The total
magnetic moment is reduced compared to the theoretical bulk value, but
still comparable to values reported for films grown at elevated
temperature. Polycrystalline Heusler films combined with MgO barriers
are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature. 相似文献
6.
R. Guirado-López D. Spanjaard M.-C. Desjonquères 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(4):459-466
The magnetic properties of small YN clusters are studied by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Several
types of cluster geometries are considered in order to see the effects of the size and symmetry of the structures on the magnetic
properties. The average magnetic moments are found to be constant over large domains of variations in the interatomic distance, a fact that can be explained by the
existing closed shell electronic configurations at least for one spin direction in all our magnetic solutions. Small energy
gains upon the onset of magnetization are obtained, which reveals the low stability of the magnetic solutions. Our results
contradict the prediction of a magnetic-nonmagnetic transition at a large cluster size (about 90 atoms) for these kinds of
systems.
Received: 27 April 1998 / Received in final form: 23 June 1998 / Accepted: 17 July 1998 相似文献
7.
We report a systematic study of the structural, electronic and magnetic properties of Cr-doped CdTe for various Cr concentrations x (=0.25, 0.5, 0.75 and 1.0) using first principles calculations based on the density functional theory (DFT). The electronic band structure of the alloy has been calculated using the Wu-Cohen (WC) as well as the Angel-Vosko (EV) generalized gradient approximation (GGA) for the exchange-correlation potential. The analysis of the density of states (DOS) curves shows the half-metallic ferromagnetic character with half-metallic gap more than 0.52 eV. While the origin of half-metallic ferromagnetism is explained, the band structure calculations are used to determine s (p)-d exchange constants N0α (conduction band) and N0β (valence band) that agree with typical magneto-optical experiment. It is found that the p-d hybridization reduces the magnetic moment of Cr from its free space charge value and produces small magnetic moments on the Cd and Te sites. Lastly, we discuss the robustness of half-metallicity with respect to the variation of lattice constants of the CrxCd1−xTe alloys. 相似文献
8.
Hangdong Wang 《Physics letters. A》2009,373(44):4092-4095
In this Letter, the single crystals of Ba5Co5ClO13 were grown by the flux method successfully. Their structure, magnetic and transport properties were studied. A large anisotropy of the magnetic and transport properties has been detected in this compound. Below the TN∼108 K, the magnetic susceptibility exhibits an antiferromagnetic peak in χc and an upturn transition in χab. We suggest that this behavior is consistent with the competition of the ferromagnetic (FM) intra-blocks coupling and antiferromagnetic (AFM) inter-blocks coupling in this compound. The temperature dependence of the resistivity displays a hump in ρab and a kink in ρc around TN, suggesting the strong coupling between the transport and magnetic properties. Above and below the transition, the transport properties in ab plane follow the three-dimensional (3D) variable range hopping (VRH) mechanism. 相似文献
9.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
10.
M. Manekar S. B. Roy 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(1):19-25
We investigate the electronic structure of
Sr2FeMoO6/SrTiO3 (SFMO/STO) multilayers using the
ab initio Full Potential Linearized Augmented Plane Wave
method in order to study their properties within the GGA and GGA+U methods. We examin more especially the role of the interface
on the magnetic and transport properties of these multilayers taking into account a possible Fe deficiency at the interface
and we show that bulk behaviour is rapidly recovered due to the strong localization of
the interfacial perturbation. For perfect interfaces, the whole structure is found half-metallic within the GGA+U method;
the situation
being ambiguous within the GGA method where SFMO is at the limit of being half-metallic depending on the structural deformation
induced by the STO layer. This leads us to the conclusion that such a system could be used as injection electrode and tunnel
barrier in magnetic tunnel junctions with a fully spin polarized injected current.
For Fe deficient interfaces, we show that the interfacial densities of states are nearly unpolarized showing that this kind
of
imperfection has potentially a strong impact on the properties
of the multilayers. 相似文献
11.
V.R. Galakhov M.A. Korotin N.A. Ovechkina E.Z. Kurmaev V.S. Gorshkov D.G. Kellerman S. Bartkowski M. Neumann 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(2):281-286
The electronic structure of LiMnO2 and Li2MnO3 was studied by means of X-ray photoelectron and soft X-ray emission spectroscopy. For LiMnO2, LSDA and LSDA+U calculations were carried out. The LSDA+U calculations are in rather good agreement with the measured valence-band structure as well as with the magnetic and electrical
properties of LiMnO2. It is shown that the band gap in LiMnO2 is determined by the charge-transfer effect.
Received 15 March 1999 and Received in final form 14 July 1999 相似文献
12.
B. Pedrini S. Wessel J. L. Gavilano H. R. Ott S. M. Kazakov J. Karpinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):219-228
We report results of susceptibility χ and 7Li NMR measurements on LiVSi2O6. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic
systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement
of V ions.
The NMR results indicate antiferromagnetic ordering below TN=24 K. The intra- and interchain coupling J and Jp for LiVSi2O6, and also for its sister compounds LiVGe2O6, NaVSi2O6 and NaVGe2O6, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations.
While Jp is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain
direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic
anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below TN, indicated by the variation of the NMR spin-lattice relaxation rate at T≪TN. 相似文献
13.
I. Živković V. P.S. Awana H. Berger 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(4):423-431
We have performed an investigation of the nonlinear magnetic response in ruthenocuprates. A negative, diverging-like peak
at the main magnetic transition TN in RuSr2
RECu2O8 (RE = Gd, Y) indicates a possible canted antiferromagnetic order. Another well defined feature above TN points to a blocking of superparamagnetic particles through the T-3 dependence of the third harmonic at higher temperatures. Below TN a nondiverging peak appears, which is strongly affected by the addition of 10% of Cu ions in the RuO2 planes. In RuSr2
RE
2-xCexCu2O10 the main magnetic transition TM is accompanied by two characteristic temperatures in the third harmonic of the ac susceptibility, in agreement with recent
studies from μSR and M?ssbauer spectroscopy. We find that the spin-spin correlation temperature is the same in both families
of ruthenocuprates. 相似文献
14.
Yoshiyuki Yoshida Kotaro Iwata Naofumi Aso 《Journal of Physics and Chemistry of Solids》2011,72(5):559-561
We have measured magnetization curves and powder neutron diffraction of double-layered Ruddlesden-Popper type ruthenate Sr3−xCaxRu2O7 (x=1.5, 2.0 and 3.0). The field dependence of the magnetization revealed that the transition field of metamagnetic transition along the b-axis shifted to lower fields and that the transition became broad with increasing Sr content. The slope of the magnetization curve also increased with increasing Sr content below the metamagnetic transition. These results indicate that an itinerant component is partly introduced by the Sr substitution. From the magnetic reflection, on cooling below TN, an additional reflection was observed at (0 0 1) for each x, and the amplitude increased with decreasing temperature. The observed diffraction patterns are very similar to those of Ca3Ru2O7. We conclude that the magnetic structure of the antiferromagnetic ordered phase is basically the same structure with that of Ca3Ru2O7. 相似文献
15.
E. García-Matres J.L Martínez J. Rodríguez-Carvajal 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):59-70
A neutron diffraction study, as a function of temperature, of the title compounds is presented. The whole family (space group
Immm, a
≈ 3.8?, b
≈ 5.8?, c
≈ 11.3?) is structurally characterised by the presence of flattened NiO6 octahedra that form chains along the a-axis, giving rise to a strong Ni-O-Ni antiferromagnetic interaction. Whereas for Y-compound only strong 1D correlations exist
above 1.5 K, presenting the Haldane gap characteristic of 1D AF chain with integer spin, 3D AF ordering is established simultaneously
for both R and Ni sublattices at temperatures depending on the rare earth size and magnetic moment. The magnetic structures
of R2BaNiO5 ( R
=
Nd, Tb, Dy, Ho, Er and Tm) have been determined and refined as a function of temperature. The whole family orders with a magnetic
structure characterised by the temperature-independent propagation vector
= (1/2, 0, 1/2). At 1.5 K the directions of the magnetic moments differ because of the different anisotropy of the rare earth ions. Except
for Tm and Yb (which does not order above 1.5 K), the magnetic moment of the R3+ cations are close to the free-ion value. The magnetic moment of Ni2+ is around 1.4
, the strong reduction with respect to the free-ion value is probably due to a combination of low-dimensional quantum effects
and covalency. The thermal evolution of the magnetic structures from T
N
down to 1.5 K is studied in detail. A smooth re-orientation, governed by the magnetic anisotropy of R3+, seems to occur below and very close to T
N
in some of these compounds: the Ni moment rotates from nearly parallel to the a-axis toward the c-axis following the R moments. We demonstrate that for setting up the 3D magnetic ordering the R-R exchange interactions cannot
be neglected.
Received 19 July 2001 相似文献
16.
We report a theoretical study of the magnetic behavior of symmetrical twined PdN (N≤220) clusters. The twined PdN particles were built from two equal PdM seed-clusters with fcc-like structure for M=38, 55, 79 and 116. The optimized geometrical structures of PdN (with N<2M) were obtained from an uniform relaxation of the fcc-like twined configurations using the embedded atom method (EAM). The spin-polarized electronic structure and related magnetic properties of those optimized geometries were calculated by solving self-consistently a spd tight-binding Hamiltonian. We observe that, in some cases the twining process may induce and/or enhance the magnetic moment of the clusters even in the case when the seed-clusters are non-magnetic. Our results also suggest a strong dependence on the twining orientation, providing further support to the influence of symmetry effects on the magnetic properties of finite transition-metal systems. We discuss our results in comparison with some recent experimental observations for Pd nanoparticles [Shinohara et al., Phys. Rev. Lett. 91 (2003) 197201. [14]; Sampedro et al., Phys. Rev. Lett. 91 (2003) 237203. [13]]. 相似文献
17.
K. Popa R.J.M. Konings F. Wastin E. Colineau N. Magnani P.E. Raison 《Journal of Physics and Chemistry of Solids》2008,69(1):70-75
The heat capacity of cerium zirconate pyrochlore, Ce2Zr2O7, was measured from 0.4 to 305 K by hybrid adiabatic relaxation method for various magnetic field strengths. Magnetisation measurements were performed on the sample also. The results revealed a low-temperature anomaly that showed Schottky-type characteristics with increasing magnetic field strength. The estimated entropy due to the magnetic ordering of the two Ce3+ moments is 1.37R, close to the theoretical value for a doublet ground state (1.39R). The enthalpy increments relative to 298.15 K were measured by drop calorimetry from 531 to 1556 K. The obtained results significantly differ from those reported in the literature; the origin of the discrepancy is due to the probable oxidation of the pyrochlore structure into fluorite. 相似文献
18.
Spin-polarized calculations were performed to investigate the structural, elastic, electronic, and magnetic properties of InCCo3 and InNCo3. The deviation of our calculated lattice parameters and equilibrium volume from experimental results is less than 0.8% and 2.5%, respectively. The obtained values of elasticity moduli Cij, bulk modulus B, and shear modulus G are discussed. From the calculated band structure and the total and partial densities of states, we have concluded that these compounds are electrical conductors; moreover, they are bonded by a mixture of covalent, ionic, and metallic bonds. Our calculations show that InCCo3 has nonmagnetic properties, while InNCo3 could have a magnetic behaviour, with an average magnetic moment about 0.54 μB/atom, which is mostly derived from d electrons of the cobalt atoms in the energy range from −5 eV up to the Fermi level. 相似文献
19.
N. Fujima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):185-188
The non-collinearity of magnetic moments of pentagonal bipyramid Cr7, Mn7 and Fe7 clusters is discussed. The magnetic moments are calculated by the discrete variational non-collinear spin-density functional
method. For the Cr7 cluster, a coplanar magnetic arrangement appears at the large interatomic distance. With decreasing the interatomic distance,
the coplanar arrangement changes to the parallel arrangement with a small absolute magnetic moment. For the Mn7 cluster, the magnetic arrangement changes from coplanar to antiparallel with decreasing the interatomic distance. Also for
the Fe7 cluster, some coplanar magnetic moments appear at the interatomic distance of 2.23 ?. In these coplanar magnetic arrangements,
the magnetic moment at the basal site of the pentagon rotates with a step of 144 degrees for the Cr7 clusters and 72 degrees for the Mn7 and Fe7 clusters.
Received 30 November 2000 相似文献
20.
T. Groń E. Malicka A.W. Pacyna R. Sitko 《Journal of Physics and Chemistry of Solids》2009,70(8):1175-1180
The magnetic and electrical properties of the Al-doped polycrystalline spinels ZnxCryAlzSe4 (0.13≤z≤0.55) with the antiferromagnetic (AFM) order and semiconducting behavior were investigated. A complex antiferromagnetic structure below a Néel temperature TN≈23 K for the samples with z up to 0.4 contrasting with the strong ferromagnetic (FM) interactions evidenced by a large positive Curie-Weiss temperature θCW decreasing from 62.2 K for z=0.13 to 37.5 K for z=0.55 was observed. Detailed investigations revealed a divergence between the zero-field-cooling (ZFC) and field-cooling (FC) susceptibilities at temperature less than TN suggesting bond frustration due to competing ferromagnetic and antiferromagnetic exchange interactions in the compositional range 0.13≤z≤0.4. Meanwhile, for z=0.55 a spin-glass-like behavior of cluster type with randomly oriented magnetic moments is observed as the ZFC-FC splitting goes up to the freezing temperature Tf=11.5 K and the critical fields connected both with a transformation of the antiferromagnetic spin spiral via conical magnetic structure into ferromagnetic phase disappear. 相似文献