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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.
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
5.
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
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