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1.
Yu. P. Gnatenko O. A. Shigil’chev E. Rutkovskii G. Contreras-Puente M. Cardenas-Garcia 《Physics of the Solid State》1998,40(4):564-568
Low-temperature photoluminescence, exciton reflection, and multiphonon resonant Raman scattering spectra of Ni-and Co-doped
Zn1−x
MnxTe crystals were investigated. Intense emission occurs in a broad spectral region (1100–17 000 cm−1) in the crystals containing Ni atoms. It is caused by intracenter transitions involving Mn2+ ions and transitions between the conduction band and a level of the doubly charged acceptor. The features of the exciton
photoluminescence and multiphonon resonant Raman scattering involving longitudinal-optical (LO) phonons at various temperatures
are investigated. The insignificant efficiency of the localization of excitons on potential fluctuations in the Zn1−x
MnxTe:Co crystals is established. A temperature-induced increase in the intensity of the 5LO multiphonon resonant Raman scattering
line due to the approach of the conditions for resonance between this line and the ground exciton state is observed in these
crystals.
Fiz. Tverd. Tela (St. Petersburg) 40, 616–621 (April 1998) 相似文献
2.
We propose a new mechanism to explain the magnetic structure of a recently discovered magnetoresistive double perovskite oxide
system, Sr2FeMoO6, with the help of detailed experimental and theoretical results. This model, based on a strong antiferromagnetic coupling
between the local moment and the charge carriers arising from local hopping interactions, can give rise to ferromagnetic metallic
as well as ferromagnetic insulating ground states. The relevance of this mechanism in understanding the magnetism in dilute
magnetic semiconductors such as Ga1 − x
Mn
x
As, is also discussed. 相似文献
3.
Summary It is shown that the behaviour of the temperature dependence of the critical current in polycrystalline thin films of high-T
c superconductors depends crucially on the assumption made concerning the nature of the intergranular material. The usual assumption
of a superconductor-insulator-superconductor (=SIS) ?sandwich? between each grain leads to a crossover fromI
c∼(1−T/T
c) toI
c∼(1−T/T
c)3/2, for temperatures nearT
c (whereI
c is the critical current,T the absolute temperature, andT
c the superconducting transition temperature). Instead, for a superconductor-normal metal-superconductor (=SNS) sandwich the
dependenceI
c∼(1−T/T
c)2 is found for all temperatures. Consideration is given to the effect of self-magnetic field on the analysis. The comparison
between expressions for continuous and granular systems is extended.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
4.
S. F. Dubinin S. G. Teploukhov V. E. Arkhipov V. D. Parkhomenko é. A. Nefeld A. V. Korolev N. A. Ugryumova Ya. M. Mukovski 《Physics of the Solid State》2007,49(4):739-745
The structural and magnetic states of Pr1−x
Sr
x
MnO3 (x = 0.22, 0.24) manganite crystals were studied over a wide temperature range. Measurements of the magnetic susceptibility
and electrical resistivity demonstrated that these manganites belong to the class of ferromagnetic semiconductors. Thermal
neutron elastic scattering patterns revealed that, in the temperature range 4.2–350 K, the manganites have an orthorhombic
structure (space group Pnma) with a well-pronounced cooperative Jahn-Teller effect. Major emphasis was placed on the nuclear magnetic superstructure
with a wave vector q = (2π/2a, 0, 2π/2c). It was shown that this superstructure suggests 1/4-type charge ordering in the manganites under investigation.
Original Russian Text ? S.F. Dubinin, S.G. Teploukhov, V.E. Arkhipov, V.D. Parkhomenko, é.A. Neĭfel’d, A.V. Korolev, N.A.
Ugryumova, Ya.M. Mukovskiĭ, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 704–710. 相似文献
5.
S. V. Grigor’ev S. A. Klimko S. V. Maleev A. I. Okorokov V. V. Runov D. Yu. Chernyshov 《Journal of Experimental and Theoretical Physics》1997,85(6):1168-1179
A magnetic phase transition in carbon-doped (0.1 and 0.7 at. %) Fe70Ni30 Invar alloys was investigated by the method of depolarization of a transmitted neutron beam and by small-angle scattering
of polarized neutrons. It is shown that for both alloys, two characteristic length scales of magnetic correlations coexist
above T
c. Small-angle scattering by critical correlations with radius R
c is described well by the Ornstein-Zernike (OZ) expression. The longer-scale (second) correlations, whose size can be estimated
from depolarization data, are not described by the OZ expression, and hypothetically can be modeled by a squared OZ expression,
which in coordinate space corresponds to the relation 〈M(r)M(0)〉∝exp(−r/R
d), where R
d is the correlation length of the second scale. The temperature dependence of the correlation radius R
c was obtained: R
c ∝ ((T−T
c)/Tc)−ν
, where ν≈2/3 is the critical exponent for ferromagnets, over a wide temperature range up to T
c
exp
, at which the correlation radius becomes constant and equals its maximum value R
c(T
c)=R
c
max
. The maximum correlation radius established (R
c
max
=140 Å and 230 Å for the first and second alloys, respectively) characterizes the length-scale of the fluctuation for which
the appearance of critical correlations first results in the formation of a ferromagnetic phase, and the phenomenon itself
exhibits a “disruption” of the second-order phase transition at T=T
c
exp
, as a result of which a first-order transition arises. Temperature hysteresis was also detected in the measured polarization
of the transmitted beam and intensity of small-angle neutron scattering in the alloy above T
c, confirming the character of this magnetic transition as a first-order transition close to a second-order transition.
Zh. éksp. Teor. Fiz. 112, 2134–2155 (December 1997) 相似文献
6.
Sunil K Sinha S Roy M R Fitzsimmons S Park M Dorn O Petracic I V Roshchin Zhi Pan Li X Batlle R Morales A Misra X Zhang K Chesnel J B Kortright Ivan K Schuller 《Pramana》2006,67(1):47-55
We discuss specular reflectivity and off-specular scattering of neutrons and X-rays from magnetic films. Both these techniques
are capable of providing information about the morphology of the chemical and magnetic roughness and the magnetic domain structure.
The use of neutrons with polarization analysis enables the spatial distribution of different vector components of the magnetization
to be determined, and the use of resonant magnetic X-ray scattering enables magnetization in a compound system to be determined
element-selectively. Thus both these methods provide powerful and complementary new probes for studying magnetism at the nanoscopic
level in a variety of systems such as those exhibiting exchange bias, giant magnetoresistance, spin injection, etc. We shall
illustrate with an example of both techniques applied to an exchange bias system consisting of a single crystal of antiferromagnetic
FeF2 capped with a ferromagnetic Co film, and discuss what has been learned about how exchange bias works in such a system. 相似文献
7.
Chen Li-chuan A. Rabenau W. Weppner 《Applied Physics A: Materials Science & Processing》1978,17(3):233-237
The ionic and electronic conductivities of Ag2Tl6I10 single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as
well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag+-ion conductor parallel toc-direction, with the Ag+ ions moving through linear channels that are not interconnected. The conductivity σ‖c
=1.6×10−7Ω−1cm−1 at 25°C, with an activation enthalpy for σ‖c
of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ⊥c
=3×10−9Ω−1cm−1 at 25°C and an activation enthalpy for σ⊥c
of 0.64 eV. This is the first observation of one-dimensional Ag+ conduction and this type of orientation-dependent change from ionic to electronic conduction.
On leave from Institute of Physics, Academia Sinica, Peking, China. 相似文献
8.
Feng Shuang-jiu Chen Chun-xia Li Guang Li Xiao-guang 《Frontiers of Physics in China》2006,1(2):243-245
The dependences of critical current density J
c on the interlayer coupling strength and magnetic field in Bi2212 crystals were obtained by measuring the magnetic loop of
the crystals with different interlayer coupling strengths. It was revealed that J
c decreases with the decrease in the interlayer coupling of the crystals. The relation of J
c ∞ exp (−H
β) was also found in the crystals, and further analysis indicated that it was the result of Zeldov pinning potential model.
__________
Translated from Chinese Journal of Low Temperature Physics, 2005, 27(1) (in Chinese) 相似文献
9.
A general solution is obtained for the lattice dynamics of a cluster ofn-impurity atoms using the double-time Green’s function formalism. The cluster is characterized byn-mass defect andm-force constant change parameters. It is shown that this general solution for the Green’s function for then-impurity cluster can also be expressed in terms of the Green’s function for the (n−1)-impurity cluster. As an application, the cluster impurity modes for a pair are calculated using the Debye model for the
host lattice dynamics. The splitting of the high frequency local modes and nearly zero frequency resonant modes due to pairs
show an oscillatory behaviour on varying the distance of separation between the two impurity atoms. These oscillations are
most prominent for two similar impurities and get damped for two dissimilar impurities or if one of the impurities produces
a force constant change. The predictions of the calculation provide qualitative explanation of the data obtained from the
infrared measurements of the resonant modes in mixed crystal system of KBr1−c
Cl
c
: Li+ and KBr1−c
I
c
: Li+. 相似文献
10.
We have derived the so-called gap equation, which determines the upper critical magnetic field, perpendicular to conducting chains of a quasi-one-dimensional superconductor. By analyzing this equation at low temperatures, we have found that the calculated angular dependence of the upper critical magnetic field is qualitatively different than that in the so-called effective mass model. In particular, our theory predicts a non-analytical angular dependence of the upper critical magnetic field, H c2(0) − H c2(α) ∼ α3/2, when magnetic field is close to some special crystallographic axis and makes an angle α with it. We discuss possible experiments on the superconductor (DMET)2I3 to discover this non-analytical dependence. 相似文献
11.
A. I. Dmitriev R. B. Morgunov S. V. Zaitsev 《Journal of Experimental and Theoretical Physics》2011,112(2):317-326
The static and high-frequency dynamic magnetic properties and photoluminescence of two-dimensional semiconductor GaAs heterostructures
containing an InGaAs quantum well and a thin manganese layer (δ layer) are studied. It is found that the Curie temperature
is T
C ≈ 35 K and the magnetic anisotropy field of the ferromagnetic manganese δ layer is H
a ≈ 600 Oe. The spin resonance spectrum exhibits a line in weak fields (from −50 to 100 Oe), which is observed in the same
temperature interval T < 40 K where the ferromagnetic ordering of the manganese δ layer occurs. This line is probably caused by the nonresonance
contribution of the spin-dependent scattering of charge carriers to the negative magnetic resistance. The dependence of the
degree of polarization of photoluminescence on the magnetic field also points to the ferromagnetic behavior of the manganese
δ layer. 相似文献
12.
M. G. Kim A. Kreyssig Y. B. Lee R. J. McQueeney B. N. Harmon A. I. Goldman 《The European physical journal. Special topics》2012,208(1):157-164
We present an X-ray resonant magnetic scattering study at the Fe-K absorption edge of the BaFe2As2 compound. The energy spectrum of the resonant scattering, together with our calculation using the full-potential linear-augmented
plane wave method with a local density functional suggests that the observed resonant scattering arises from electric dipole
(E1) transitions. We discuss the role of Fe K-edge X-ray resonant magnetic scattering in understanding the relationship between the structure and the antiferromagnetic
transition in the doped Ba(Fe1−x
Co
x
)2As2 superconductors. 相似文献
13.
M. A. Zelikman 《Physics of the Solid State》1997,39(11):1751-1755
A system of pancake vortices formed near the boundary of a sample in a monotonically increasing external magnetic field is
calculated with allowance for pinning due to the cellular structure of the medium for various values of the pinning parameter
I, which is proportional to the critical current of the junction and the cell diameter. The shortest distance from the outermost
vortex to the nearest neighbor is proportional to I
−11. It is shown that the pinning parameter has a critical value I
c separating two regimes with different types of critical states. For I<I
c the external magnetic field has a threshold value H
t(I), above which the field immediately penetrates the interior of the junction to an infinite distance. For I>I
c the magnetic field decays linearly from the boundary into the interior of the junction. The value obtained in the study,
I
c=3.369, differs from the value of 0.9716 postulated by other authors. The dependence of the slope of the magnetic field profile
near the boundary on I is determined. It is shown that the slope is independent of I in intervals 2πk<I<2πk+π.
Fiz. Tverd. Tela (St. Petersburg) 39, 1958–1963 (November 1997) 相似文献
14.
A. A. Mukhin V. Yu. Ivanov A. M. Kuz’menko A. S. Prokhorov A. A. Pronin S. N. Barilo G. L. Bychkov S. V. Shiryaev 《JETP Letters》2010,91(3):147-154
The effect of the substitution of Co2+, Mn2+, and Zn2+ ions for Ni2+ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni1 − x
T
x
)3V2O8 has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure.
The existence region of this state is expanded to low temperatures down to 3 K for Zn2+ and below 1.8 K for Co2+ and Mn2+ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears
completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has
been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure.
The corresponding H-T phase diagrams have been drawn. 相似文献
15.
Thin films of ZnSe and PEO–chitosan blend polymer doped with NH4I and iodine crystals were prepared to form the two sides of a semiconductor electrolyte junction. ZnSe was electrodeposited
on indium tin oxide (ITO) conducting glass. The polymer is a blend of 50 wt% chitosan and 50 wt% polyethylene oxide. The polymer
blend was complexed with ammonium iodide (NH4I), and some iodine crystals were added to the polymer–NH4I solution to provide the I−/I3−redox couple. The room temperature ionic conductivity of the polymer electrolyte is 4.32 × 10−6 S/cm. The polymer film was sandwiched between the ZnSe semiconductor and an ITO glass to form a ZnSe/polymer electrolyte/ITO
photovoltaic cell. The open circuit voltage (V
oc) of the fabricated cells ranges between 200 to 400 mV and the short circuit current between 7 to 10 μA. 相似文献
16.
D. G. Haase C. R. Gould J. E. Koster N. R. Roberson L. W. Seagondollar J. P. Soderstrum M. B. Schneider X. Zhu 《Hyperfine Interactions》1988,43(1-4):133-138
We describe searches for parity and time reversal violations in the scattering of polarized neutrons from polarized and aligned165Ho targets. We have completed a search with 7.1 and 11.0 MeV neutrons for PoddTodd terms in the elastic scattering forward amplitude of the form s. (I×K), wheres is the neutron spin,I is the target spin andk is the neutron momentum vector. The target was a single crystal of holmium, polarized horizontally along itsb axis by a 1 Tesla magnetic field. The neutrons were polarized vertically. Differences in the neutron transmission were measured
for neutrons with spins parallel (antiparallel) toI×k. The P,T violating analyzing powers were found to be consistent with zero at the few 10−3 level: ρP,T(7.1 MeV)=−0.88 (±2.02) x 10−3, ρP,T(11.0 MeV)=−0.4 (±2.88) x 10−3. We have also attempted to find enhancements with MeV neutrons in P-violation due to the term s\k. We are preparing an aligned target cryostat for investigations of PevenTodd terms {bd(I\k)(I×k)\s} in neutron scattering. The target will be a single crystal cylinder of165Ho cooled to 100 mK in a bath of liquid helium and rotated by a shaft from a room temperature stepping motor. The cylinder
will be oriented vertically and the alignment (c) axis oriented horizontally. Warming or rotation of the sample allows one to separate effects that mimic the sought-after
time reversal violating term. 相似文献
17.
Florin Radu Alexei Nefedov Johannes GrabisGregor Nowak Andre BergmannHartmut Zabel 《Journal of magnetism and magnetic materials》2006
We have used soft X-ray resonant magnetic scattering (XRMS) to search for the presence of an effective ferromagnetic moment belonging to the antiferromagnetic (AF) layer which is in close contact with a ferromagnetic (F) layer. Taking advantage of the element specificity of the XRMS technique, we have measured hysteresis loops of both Fe and CoO layers of a CoO(40 Å)/Fe (150 Å) exchange bias bilayer. From these measurements we have concluded that the proximity of the F layer induces a magnetic moment in the AF layer. The F moment of the AF layer has two components: one is frozen and does not follow the applied magnetic field and the other one follows in phase the ferromagnetic magnetization of the F layer. The temperature dependence of the F components belonging to the AF layer is shown and discussed. 相似文献
18.
We report measurements of non-linear charge transport in epitaxial (La1−x
Pr
x
)0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the
highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage
characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven
charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters
dispersed in a CO background. 相似文献
19.
A. V. Pashchenko V. P. Pashchenko A. G. Sil’cheva V. K. Prokopenko A. A. Shemyakov Yu. F. Revenko V. P. Komarov S. V. Gorban’ 《Physics of the Solid State》2011,53(2):309-315
The structure and properties of lanthanum strontium manganite perovskites La0.6Sr0.2Mn1.2 − y
Cr
y
O3 ± δ (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic (χac and 55Mn NMR) methods. The parameter of the rhombohedrally distorted (R
$
\bar 3
$
\bar 3
c) perovskite structure decreases with increasing y. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis
of asymmetrically broadened 55Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn3+ ↔ Mn4+ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content
leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic
phase transition temperatures (T
ms
and T
c
) due to the distortion of the exchange interactions Mn3+ ↔ Mn4+ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation
energy. The magnetoresistive effect near T
ms
and T
c
is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature
effect is associated with the tunneling on mesostructural intercrystallite boundaries. 相似文献
20.
An experimental study is reported of the effect of an electric field E⩽120 MV/m and of temperature T on the critical current I
c and I-V characteristics of yttrium-based high-T
c superconducting ceramics. The materials studied were copper-deficient ceramics, YBa2Cu3−x
Oy (D samples), and YBa2Cu3−x
Oy/Agx ceramics [S samples with silver present in amounts equal to the copper deficiency (0⩽x⩽0.4)]. It has been established that in D samples at 77 K, the electric field increases I
c and reduces substantially R for I>I
c, whereas in S samples no field effect is observed. Measurements of the I
c(T) dependence near the critical temperature showed that they can be described for all samples by a relation of the type I
c
=const(1−T/T
c
)α, where α≈1 for the D samples, and α≈2 for the S samples. The results obtained suggest that the electric-field effect correlates with the existence in the ceramic of SIS-type weak links at grain boundaries.
Fiz. Tverd. Tela (St. Petersburg) 40, 1195–1198 (July 1998) 相似文献