共查询到20条相似文献,搜索用时 15 毫秒
1.
Karen B. Paul 《Central European Journal of Physics》2005,3(1):115-126
A monocrystal ofFe
3
O
4 is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and
magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT
v
=123.76 K with activation energy E=92.5 meV at T >T
v
and temperature-substitute for the activation energy below the VT,T
0=E/k
B
≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change
in the magnetic moment ΔM≈0.21 ΔM≈0.21μ
B
and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT
v
. The magnetic characterization established self consistentlyT
v
as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ
B
and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization
of the monocrystal (88%) with additional natural and imposed defects contributing as 12%. 相似文献
2.
The results of the detailed scanning electron microscopy study of PrBa2Cu3O7-δ single crystals after the long-lasting high-temperature post-growth treatment are reported. The presence of the unstable
decomposition products on the crystal surface indicates that the onset of superconductivity must be related to the structural
transformations in the bulk (approximately 20% of the total volume of the examined crystals). The time-dependent character
of the superconductivity in the Pr-123 crystals could be attributed to the migration of defects in the Pr−Ba sublattice from
the bulk toward the surface. 相似文献
3.
Pavel Svoboda Pavel Javorský Fuminori Honda Vladimír Sechovský Alois A. Menovsky 《Central European Journal of Physics》2004,2(2):397-418
The tetragonal compound UNi2Si2 exhibits in zero magnetic field three different antiferromagnetic phases belowT
N
=124 K. They are formed by ferromagnetic basal planes, which are antiferromagnetically coupled along thec-axis with the propagation vectorq=(0, 0, q
z
). Two additional order-order magnetic phase transitions are observed below T
N
, namely atT
1=108 K and T
2=40 K in zero magnetic field. All three phases exhibit strong uniaxial anisotropy confining the U moments to a direction parallel
to the c-axis. UNi2Si2 single crystals were studied in detail by measuring bulk thermodynamic properties, such as thermal expansion, resistivity,
susceptibility, and specific heat. A microscopic study using neutron diffraction was performed in magnetic fields up to 14.5
T parallel to the c-axis, and a complex magnetic phase diagram has been determined. Here, we present the analysis of specific-heat data measured
in magnetic fields up to 14 T compared with the results of the neutron-diffraction study and with other thermodynamic properties
of UNi2Si2. 相似文献
4.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
5.
On SrTiO3 single crystal substrate, by using the pulsed electron deposition technique, the high-quality electron doped Nd1.85Ce0.15CuO4−δ
superconducting film was successfully fabricated. After careful study on the R-T curves of the obtained samples deposited with different substrate temperatures, thicknesses, annealing methods and pulse
frequencies, the effects of them on the superconductivity of the films were found, and the reasons were also analyzed. Additionally,
by using the same model of the pulsed laser deposition technique, the relation between the target-to-substrate distance and
the deposition pressure was drawn out as a quantitative one.
Supported by the Key Project of Zhejiang Provincial Natural Science Foundation (Grant No. Z605131), the ‘100 Talents Project’
of Chinese Academy of Sciences, the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001)
and the National Natural Science Foundation of China (Grant No. 60571029) 相似文献
6.
Alexander G. Andreev Stefka G. Tsintsarska Maria Dimitrova-Ivanovich Ivaylo Polyanski Mladen Georgiev Alexander D. Gochev 《Central European Journal of Physics》2004,2(2):329-356
The temperatureT dependencies ρ(T) of normal state electric resistivitiesρ
c
(axial) andρ
ab
(in plane) of single-layer high-T
c
superconductors show common trends: AsT is raised, the resistivity first drops steeply before it starts rising αT above an apparent semiconductor-to-metal crossoverT
cross
. To analyze ρ(T) we plottT/ρ againstT at various dopingsx for bothρ
c
andρ
ab
.T/ρ is inversely proportional to the traversal time across a potential barrier as an ionic particle drifts in an electric field.
We findT/ρ in good agreement with theT dependence of the quantum rate of migrating particles: AsT is raised, a zero-point rate at the lowestT is extended to a nearly flat plateau before a thermally activated branch sets in. We also find evidence for the admixture
of 1- & 2-phonon absorptions below the Arrhenius range. These features shape the semiconductor-like branch below T
cross
. AboveT
cross
a metallic-like branch sets in, its αT character deriving from the field coupling of the migrating particle. Our analysis suggests that metal physics may not suffice
if ionic features play a role in transport. We attribute our conclusions to the drift of strong-coupling polarons along Cu−O
bonds. These “bond polarons” originate from carrier scattering by double-well potentials associated with the bonds. A bond
polaron dissociates to a free hole as it passes onto a neighboring O-O link. 相似文献
7.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
8.
A. A. Mukhin G. P. Vorob’ev V. Yu. Ivanov A. M. Kadomtseva A. S. Narizhnaya A. M. Kuz’menko Yu. F. Popov L. N. Bezmaternykh I. A. Gudim 《JETP Letters》2011,93(5):275-281
The colossal (more than threefold) decrease in the dielectric constant ɛ in the easy-plane SmFe3(BO3)4 ferroborate in a magnetic field of ∼5 kOe applied in the basal ab plane of the crystal has been found. A close relation of this effect to anomalies in the field dependence of the electric
polarization has been established. It has been shown that this magnetodielectric effect is due to the contribution to ɛ from
the electric susceptibility, which is related to the rotation of spins in the ab plane, arises in the region of the antiferromagnetic ordering T < T
N
= 33 K, and is suppressed by the magnetic field. A theoretical model describing the main features of the behavior of ɛ and
electric polarization in the magnetic field has been proposed, taking into account the additional anisotropy in the basal
plane induced by the magnetoelastic stresses. 相似文献
9.
By taking into account slight interactions, i.e. spin-spin, spin-other-orbit and orbit-orbit interactions, in addition to
spin-orbit interaction, the zero-field splitting of 4
T
2 state for 3d3 ions at tetragonal symmetry has been studied. The convergence of the approximation perturbation formula of 4
T
2 state for 3d3 ions at tetragonal symmetry has been investigated, and the contributions to zero-field splitting arising from magnetic interaction
and tetragonal crystal field are discussed. It is found that there exists combined mechanism between magnetic interactions
and tetragonal crystal field.
相似文献
10.
A facile room-temperature synthesis has been developed to prepare colloidal Mn3O4 and γ-Fe2O3 nanoparticles (5 to 25 nm) by an ultrasonic-assisted method in the absence of any additional nucleation and surfactant. The
morphology of the as-prepared samples was observed by transmission electron microscopy. High-resolution transmission electron
microscopy observations revealed that the as-synthesized nanoparticles were single crystals. The magnetic properties of the
samples were investigated with a superconducting quantum interference device magnetometer. The possible formation process
has been proposed. 相似文献
11.
There has been an increasing interest towards the incorporation of nanosize ceramic fillers in polymer electrolytes. Solid
polymer electrolytes based on polyvinylidene fluoride (PVDF), silver triflate (AgCF3SO3), and x wt% of aluminum oxide (Al2O3) nanopowders (where x = 1, 3, 5, and 10, respectively) have been prepared using solution casting technique. The structural characteristics of these
thin film specimens were studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) patterns at room temperature.
The appearance of new absorption bands and gradual shifts observed in some characteristic peaks confirmed the complex formation
between polyvinylidene fluoride and silver triflate. Furthermore, the addition of nanosized filler Al2O3 has also indicated the interaction of the filler with the polymer salt complex. The XRD patterns obtained for all these samples
in the 2θ range 10° to 70° showed the amorphous nature of these samples.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9,
2006. 相似文献
12.
We show that for every set of discrete polynomials y
n
(x(s)) on the lattice x(s), defined on a finite interval (a, b), it is possible to construct two sets of dual polynomials z
k
(ξ(t)) of degrees k = s-a and k = b-s-1. Here we do this for the classical and alternative Hahn and Racah polynomials as well as for their q-analogs. Also we establish the connection between classical and alternative families. This allows us to obtain new expressions
for the Clerbsch-Gordan and Racah coefficients of the quantum algebra U
q
(su(2)) in terms of various Hahn and Racah q-polynomials.
Dedicated to the memory of our teacher and friend Arnold F. Nikiforov (18.11.1930–27.12.2005). 相似文献
13.
Equilibrium geometries, charge distributions, stabilities and electronic properties of the Ag-adsorbed (MgO)
n
(n = 1–8) clusters have been investigated by density functional theory (DFT) with generalized gradient approximation (GGA) for
exchange-correlation functional. The results show that hollow site is energetically preferred for n⩾4, and the incoming Ag atoms tend to cluster on the existing Ag cluster. The Mulliken populations indicate that the interaction
between the Ag atom and Magnesia clusters is mainly induced by a weak atomic polarization. The adsorbed Ag atom only causes
charge redistributions of the atoms near itself. The effect of the adsorbed Ag atom on the bonding natures and structural
features of Magnesia clusters is minor. Furthermore, the investigations on the first energy difference, fragmentation energies
and electron affinities show that the Ag(MgO)4 and Ag(MgO)6 are the most stable among studied clusters.
Supported by the Startup Fund of High-level Personal for Shihezi University (Grant No. RCZX200747) 相似文献
14.
Yong-Yeon Keum 《Pramana》2004,63(6):1151-1170
We discuss applications of the perturbative QCD approach in the exclusive non-leptonic two-bodyB-meson decays. We briefly review its ingredients and some important theoretical issues on the factorization approach. PQCD
results are compatible with present experimental data for charmless B-meson decays. We predict the possibility of large direct
CP asymmetry in B0 → π+π− (23 +7%) and B0 →K
+π− (− 17 ± 5%). We also investigate the branching ratios, CP asymmetry and isospin symmetry breaking in radiativeB →(K*/ρ)γ decays. 相似文献
15.
Zhaoxia Bi Rong Zhang Weiping Li Xusheng Wang Shulin Gu Bo Shen Yi Shi Zhiguo Liu Youdou Zheng 《中国科学G辑(英文版)》2003,46(1):41-46
With the solid phase reaction between pulsed-laser-deposited (PLD) ZnO film and α-Al2O3 substrate, ZnAl2O4/α-Al2O3 complex substrates were synthesized. X-ray diffraction (XRD) spectra show that as the reaction proceeds, ZnAl2O4 changes from the initial (111)-oriented single crystal to poly-crystal, and then to inadequate (111) orientation. Corresponding
scanning electron microscope (SEM) images indicate that the surface morphology of ZnAl2O4 transforms from uniform islands to stick structures, and then to bulgy-line structures. In addition, XRD spectra present
that ZnAl2O4 prepared at low temperature is unstable at the environment of higher temperature. On the as-obtained ZnAl2O4/α-Al2O3 substrates, GaN films were grown without any nitride buffer using light-radiation heating low-pressure MOCVD (LRH-LP-MOCVD).
XRD spectra indicate that GaN film on this kind of complex substrate changes fromc-axis single crystal to poly-crystal as ZnAl2O4 layer is thickened. For the single crystal GaN, its full width at half maximum (FWHM) of X-ray rocking curve is 0.4°. Results
indicate that islands on thin ZnAl2O4 layer can promote nucleation at initial stage of GaN growth, which leads to the (0001)-oriented GaN film. 相似文献
16.
Silvete C. Guerini David L. Azevedo Maria C. A. Lima Ivana Zanella Josué Mendes Filho 《Central European Journal of Physics》2008,6(1):105-108
This paper deals with quantum mechanical interaction of no
3− with (5,5) and (8,0) swcnts. To perform this we have made an ab initio calculation based on the density functional theory. In these framework the electronic density plays a central role and it
was obtained of a self-consistent field form. It was observed through binding energy that NO3− molecule interacts with each nanotube in a physisorption regime. We propose these swcnts as a potential filter device due to reasonable interaction with NO3− molecule. Besides this type of filter could be reusable, therefore after the filtering, the swcnts could be separated from NO3− molecule.
相似文献
17.
Nanoscale yttrium–barium–copper oxide (Y2BaCuO5, Y211) particles were synthesized using the emulsion method and the solution method. The basic water-in-oil (w/o) emulsion
system consisted of n-octane (continuous oil phase), cetyltrimethylammonium bromide (cationic surfactant), butanol (cosurfactant) and water. The
composition of the emulsion system was varied and characterized by measuring the conductivity of the solutions and droplet
size. The droplet size of emulsion was determined by using the dynamic light scattering method. The water content, cosurfactant
content, and surfactant/n-octane ratio affected the droplet size which was in the range of 3–8 nm, and hence the w/o emulsion system was referred to
as a nano-emulsion system. A model was used to verify the droplet size. The influence of salt (Y2(NO3)3) content on the droplet size was investigated and the addition of salt reduced the droplet size. The effects of reaction
time and temperature on the Y211 particle sizes were also investigated. The particles were characterized using the TEM, SEM,
and XRD. Nanoparticles produced by the nano-emulsion method were calcined at 850°C to form the Y211 phase as compared to solid
state processing temperature of 1050°C. Based on the TEM analysis, the average diameter of the Y211 particles produced using
the nano-emulsion method was in the range of 30–100 nm. The effect of adding 15% Y211 nanoparticles to the superconductor
YBCO-123 as flux pinning centers, was investigated, and the transition temperature was reduced by 3 K. 相似文献
18.
Pramod Bhatt E. Carlegrim A. Kanciurzewska M. P. de Jong M. Fahlman 《Applied Physics A: Materials Science & Processing》2009,95(1):131-138
Thin film iron-tetracyanoethylene Fe(TCNE)
x
, x∼2, as determined by photoelectron spectroscopy, was grown in situ under ultra-high vacuum conditions using a recently developed
physical vapor deposition-based technique for fabrication of oxygen- and precursor-free organic-based molecular magnets. Photoelectron
spectroscopy results show no spurious trace elements in the films, and the iron is of Fe2+ valency. The highest occupied molecular orbital of Fe(TCNE)
x
is located at ∼1.7 eV vs. Fermi level and is derived mainly from the TCNE− singly occupied molecular orbital according to photoelectron spectroscopy and resonant photoelectron spectroscopy results.
The Fe(3d)-derived states appear at higher binding energy, ∼4.5 eV, which is in contrast to V(TCNE)2 where the highest occupied molecular orbital is mainly derived from V(3d) states. Fitting ligand field multiplet and charge
transfer multiplet calculations to the Fe L-edge near edge X-ray absorption fine structure spectrum yields a high-spin Fe2+ (3d6) configuration with a crystal field parameter 10Dq∼0.6 eV for the Fe(TCNE)
x
system. We propose that the significantly weaker Fe-TCNE ligand interaction as compared to the room temperature magnet V(TCNE)2 (10Dq∼2.3 eV) is a strongly contributing factor to the substantially lower magnetic ordering temperature (T
C
) seen for Fe(TCNE)
x
-type magnets. 相似文献
19.
Jing Zhang Zheng Chen MingYi Zhang QingBo Lai YanLi Lu YongXin Wang 《中国科学G辑(英文版)》2009,52(8):1154-1160
Microscopic phase field simulation is performed to study antisite defect type and temporal evolution characteristic of D022-Ni3V structure in Ni75Al
x
V25−x
ternary system. The result demonstrates that two types of antisite defect VNi and NiV coexist in D022 structure; however, the amount of NiV is far greater than VNi; when precipitates transform from D022 singe phase to two phases mixture of D022 and L12 with enhanced Al:V ratio, the amount of VNi has no evident response to the secondary L12 phase, while NiV exhibits a definitely contrary variation tendency: NiV rises without L12 structure precipitating from matrix but declines with it; temporal evolution characteristic and temperature dependent antisite
defect VNi, NiV are also studied in this paper: The concentrations of the both defects decline from high antistructure state to equilibrium
level with elapsed time but rise with elevated temperature; the ternary alloying element aluminium atom occupies both α and
β sublattices of D022 structure with a strong site preference of substituting α site.
Supported by the National Natural Science Foundation of China (Grant Nos. 50671084 and 50875217), the Doctorate Foundation
of Northwestern Polytechnical University of China (Grant No. CX200806), the China Postdoctoral Science Foundation Funded Project
(Grant No. 20070420218), and the Natural Science Foundation of Shaanxi Province of China 相似文献
20.
I. Perelshtein N. Perkas Sh. Magdassi T. Zioni M. Royz Z. Maor A. Gedanken 《Journal of nanoparticle research》2008,10(1):191-195
A new method of dispersing the aggregated strontium hexaferrite (SrFe12O19) magnetic nanoparticles in organic solvents such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol (PG),
and glycerol, by an ultrasonic bath is reported herein. The particles size of SrFe12O19 after treatment with the PGMEA is in the range 70–100 nm. The structure of dispersed SrFe12O19 was characterized using transmission electron microscopy (TEM), high resolution scanning electron microscopy (HR SEM) and
thermo gravimetric analysis (TGA). This dispersed material was used for the preparation of a topical magnetic cosmetic product
as follows: The dispersion of SrFe12O19 in PG was mixed with “Dermud-Ahava Body Cream”, an ‘oil in water’ emulsion of a Dead Sea mineral cosmetic, “AHAVA”, and the
magnetic properties of the created composite were determined. The ferrimagnetic behavior of the composite has been demonstrated
as being very similar to the behavior of strontium hexaferrite itself. 相似文献