共查询到20条相似文献,搜索用时 671 毫秒
1.
L. Kovács M. Mazzera E. Beregi R. Capelletti 《Applied physics. B, Lasers and optics》2009,94(2):273-277
Several weak absorption bands have been observed in the optical absorption spectra of pure and rare-earth-doped YAl3(BO3)4 single crystals in the 3350– 3650 cm−1 wave number region. Two of them, peaking at about 3377 cm−1 and 3580 cm−1 in the 8 K spectra, appear in most of the samples. They are tentatively attributed to the stretching mode of OH− ions incorporated in the crystal during the growth. An additional absorption band at about 5250 cm−1 at 8 K has also been detected in almost all samples. The temperature and polarization dependences of these bands, and their
possible origin, are discussed. 相似文献
2.
D. A. Erofeev E. P. Chukalina L. N. Bezmaternykh I. A. Gudim M. N. Popova 《Optics and Spectroscopy》2016,120(4):558-565
The transmission spectra of HoFe3(BO3) multiferroic single crystals are studied by optical Fourier-transform spectroscopy at temperatures of 1.7–423 K in polarized light in the spectral range 500–10 000 cm–1 with a resolution up to 0.1 cm–1. A new first-order structural phase transition close to the second-order transition is recorded at Tc = 360 K by the appearance of a new phonon mode at 976 cm–1. The reasons for considerable differences in Tc for different samples of holmium ferroborate are discussed. By temperature variations in the spectra of the f–f transitions in the Ho3+ ion, we studied two magnetic phase transitions, namely, magnetic ordering into an easy-plane structure as a second-order phase transition at TN = 39 K and spin reorientation from the ab plane to the c axis as a first-order phase transition at TSR = 4.7 ± 0.2 K. It is shown that erbium impurity in a concentration of 1 at % decreases the spin-reorientation transition temperature to TSR = 4.0 K. 相似文献
3.
S. A. Ahmed 《Applied Physics A: Materials Science & Processing》2008,92(3):565-570
Thermoelectric power and electrical resistivity measurements on polycrystalline samples of Bi2Se3 and stoichiometric ternary compound in the quasi-binary system SnSe–Bi2Se3 in the temperature range of 90–420 K are presented and explained assuming the existence of an impurity band. The variation
of the electron concentration with temperature above 300 K is explained in terms of the thermal activation of a shallow donor,
by using a single conduction band model. The density of states effective mass m
*=0.15m
0 of the electrons, the activation energy of the donors, their concentration, and the compensation ratio are estimated. The
temperature dependence of the electron mobility in conduction band is analyzed by taking into account the scattering of the
charge carriers by acoustic phonon, optical phonon, and polar optical phonon as well as by alloy and ionized impurity modes.
On the other hand, by considering the two-band model with electrons in both the conduction and impurity bands, the change
in the electrical resistivity with temperature between 420 and 90 K is explained. 相似文献
4.
M. Cazayous A. Sacuto D. Lebeugle D. Colson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(2):209-212
We have performed Raman measurements on high energy excitations in BiFeO3 single crystals as a function of both temperature and laser excitation lines. A strong feature observed at 1250 cm-1 in the Raman spectra has been previously assigned to two phonon overtone. This peak exhibits an unusual frequency shift with
the laser lines and the temperature dependence of its Fano lineshape shows two singularities at 150 K and 200 K which can
be related to magnetic excitations. In the same energy range, we have also identified the two-magnon excitation with a temperature
dependence very similar to the one measured for the one-magnon modes. 相似文献
5.
V. P.S. Awana A. Vajpayee M. Mudgel V. Ganesan A. M. Awasthi G. L. Bhalla H. Kishan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(3):281-294
We report synthesis, structure/micro-structure, resistivity under magnetic
field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity
κ(T), and magnetization of ambient pressure argon annealed
polycrystalline bulk samples of MgB2, processed under identical
conditions. The compound crystallizes in hexagonal structure with space
group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs
showing various types of defect features along with the presence of 3–4 nm
thick amorphous layers forming the grain boundaries of otherwise crystalline
MgB2. Raman spectra of the compound at room temperature exhibited
characteristic phonon peak at 600 cm-1. Superconductivity is observed
at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power
S(T), and thermal conductivity κ(T) measurements. The power law fitting
of ρ(T) give rise to Debye temperature (ΘD) at 1400 K which is
found consistent with the theoretical fitting of S(T), exhibiting Θ
D of 1410 K and carrier density of 3.81 × 1028/m3. Thermal
conductivity κ(T) shows a jump at 38 K, i.e., at Tc, which was
missing in some earlier reports. Critical current density (Jc) of up to
105 A/cm2 in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K
is seen from magnetization measurements. The irreversibility field, defined
as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe
at 4, 10 and 20 K respectively. The superconducting performance parameters
viz. irreversibility field (Hirr) and critical current density
Jc(H) of the studied MgB2 are improved profoundly with addition of
nano-SiC and nano-diamond. The physical property parameters measured for
polycrystalline MgB2 are compared with earlier reports and a
consolidated insight of various physical properties is presented. 相似文献
6.
J. Lu A. Günther F. Schrettle F. Mayr S. Krohns P. Lunkenheimer A. Pimenov V. D. Travkin A. A. Mukhin A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(4):451-460
Magnetic dc susceptibility between 1.5 and 800 K, ac
susceptibility and magnetization, thermodynamic properties, temperature
dependence of radio and audio-wave dielectric constants and conductivity,
contact-free dielectric constants at mm-wavelengths, as well as
ferroelectric polarization are reported for single crystalline BiFeO3.
A well developed anomaly in the magnetic susceptibility signals the onset of
antiferromagnetic order close to 635 K. Beside this anomaly no further
indications of phase or glass transitions are indicated in the magnetic dc
and ac susceptibilities down to the lowest temperatures. The heat capacity
has been measured from 2 K up to room temperature and significant
contributions from magnon excitations have been detected. From the
low-temperature heat capacity an anisotropy gap of the magnon modes of the
order of 6 meV has been determined. The dielectric constants measured in
standard two-point configuration are dominated by Maxwell-Wagner like
effects for temperatures T > 300 K and frequencies below 1 MHz. At lower
temperatures the temperature dependence of the dielectric constant and loss
reveals no anomalies outside the experimental errors, indicating neither
phase transitions nor strong spin phonon coupling. The temperature
dependence of the dielectric constant was measured contact free at microwave
frequencies. At room temperature the dielectric constant has an intrinsic
value of 53. The loss is substantial and strongly frequency dependent
indicating the predominance of hopping conductivity. Finally, in small thin
samples we were able to measure the ferroelectric polarization between 10
and 200 K. The saturation polarization is of the order of 40 μC/cm2, comparable to reports in literature. 相似文献
7.
D. P. Kozlenko Z. Jirák N. O. Golosova B. N. Savenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):327-334
The crystal and magnetic structure of the perovskite-like, oxygen deficient
cobalt oxide YBaCo2O5.5 has been studied by means of neutron and
X-ray diffraction in the 10–300 K temperature range. The magnetic ground
state is characterized by a coexistence of two distinct antiferromagnetic
phases. In the first one, the ionic moments of high-spin Co3+ ions in
the pyramidal sites are ordered in a spiral arrangement, while octahedral
sites are non-magnetic due to presence of low-spin Co3+ ions. The
arrangement in the second phase is collinear of the G-type, with non-zero
moments both in pyramidal (high-spin Co3+ ions) and octahedral sites
(presumably a mixture of the low- and high-spin states). With increasing
temperature, at 260–300 K, the system develops a gradual structural
transformation, which is associated with appearance of spontaneous magnetic moment.
This process is related to a thermally induced reversion of low- and
high-spin states at the octahedral sites to the intermediate-spin Co3+
states, resulting in an insulator-metal transition at TC ≈
TIM ≈ 295 K. 相似文献
8.
M. N. Popova E. A. Romanov S. A. Klimin E. P. Chukalina B. V. Mill G. Dhalenne 《Physics of the Solid State》2005,47(8):1497-1503
Diffuse transmittance spectra of polycrystalline samples of chain nickelate Nd2BaNiO5 were measured with high resolution (0.1 cm-1) over wide ranges of wavenumbers (1500–20000 cm-1) and temperatures (4.2–300 K). The energies of 54 Stark sublevels of the Nd3+ ion and exchange splittings of some of them were determined in the magnetically ordered state of Nd2BaNiO5 (T N = 47.5 ± 1 K). It was shown that the low-temperature magnetic properties of Nd2BaNiO5 are determined by exchange splitting (32 cm-1) of the ground state. 相似文献
9.
M. Schmidt Ch. Kant T. Rudolf F. Mayr A. A. Mukhin A. M. Balbashov J. Deisenhofer A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):411-418
We provide a detailed study of the reflectivity of multiferroic TbMnO3 for wave numbers from
40 cm-1 to 1000 cm-1 and temperatures 5 K < T < 300 K. Excitations are studied for
polarization directions E || a, the polarization where electromagnons are observed,
and for E || c, the direction of the spontaneous polarization in this material. The
temperature dependencies of eigenfrequencies, damping constants and polar strengths of all modes are studied and
analyzed. For E || a and below the spiral ordering temperature of about 27 K we
observe a transfer of optical weight from phonon excitations to electromagnons, which mainly involves
low-frequency phonons. For E || c an unusual increase of the total polar strength and
hence of the dielectric constant is observed indicating significant transfer of dynamic charge probably within
manganese-oxygen bonds on decreasing temperatures. 相似文献
10.
G. A. Komandin A. S. Prokhorov V. I. Torgashev E. S. Zhukova B. P. Gorshunov A. A. Bush 《Physics of the Solid State》2011,53(4):736-744
The spectra of complex permittivity of a Ba2Mg2Fe12O22 single crystal belonging to the family of Y-type hexaferrites have been measured over a wide temperature range (10–300 K) with the aim of determining the dynamic parameters
of the phonon and magnetic subsystems in the terahertz and infrared frequency ranges (3–4500 cm−1). A factor-group analysis of the vibrational modes has been performed, and the results obtained have been compared with the
experimentally observed resonances. The oscillator parameters of all nineteen phonon modes of E
u
symmetry, which are allowed by the symmetry of the Ba2Mg2Fe12O22 crystal lattice, have been calculated. It has been found that, at temperatures below 195 and 50 K, the spectral response
exhibits new absorption lines due to magnetic excitations. 相似文献
11.
E. A. Popov 《Russian Physics Journal》2004,47(10):988-994
A fine structure of the optical absorption spectrum of antiferromagnetic NaMnCl3 was measured around 23800 cm–1 at temperatures in the range 1.8–50 K in magnetic fields up to 200 kOe. The fact that the intralayer ferromagnetic interaction in the crystal possessing a layered magnetic structure is stronger than the interlayer antiferromagnetic interaction leads to the formation of intensive hot exciton-magnon absorption bands. The special features of the exciton-magnon band structure in the crystal are connected with the special features of magnon dispersion and density of exciton-magnon states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 23–28, October, 2004. 相似文献
12.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(5):721-723
Optical absorption spectra of the trigonal crystal of TbFe3(BO3)4 in the vicinity of the 7F6 → 5D4 transition in a Tb3+ ion were studied as a function of temperature (2–70 K) and magnetic field strength (0–60 kOe) at 2 K. The splitting of the
excited states of Tb3+ due to both the magnetic ordering of iron and an external magnetic field was determined. Abrupt splitting of the absorption
lines of Tb3+ at temperature TN of the magnetic ordering of the subsystem of iron was revealed, suggesting that the nature of such splitting is not entirely
magnetic. 相似文献
13.
J. Lecointre D. S. Belic J. J. Jureta R. Janev P. Defrance 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,50(3):265-278
Absolute cross sections for electron-impact dissociative excitation and
ionization of CD+
4 leading to formation of ionic products (CD2+
4, CD+
3, CD+
2, CD+, C+, D+
3, D+
2, and D+) have been measured. The animated crossed-beams
method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections
are found to be (3.8±0.2) ×10-19 cm2,
cm2,
(7.1±0.8) ×10-17 cm2, (9.0±0.8) ×
10-17 cm2 and (3.7±0.4) ×10-17 cm2 for the
heavy carbonaceous ions CD2+
4, CD+
3, CD+
2, CD+ and C+ respectively. For the light fragments, D+
3, D+
2, and D+, the cross sections around the maximum are
found to be (5.0±0.6) ×10-19 cm2, (1.7±
0.2) ×10-17 cm2 and (10.6±1.0) ×10-17 cm2, respectively. The cross sections are presented in closed analytic
forms convenient for implementation in plasma simulation codes. The analysis
of ionic product velocity distributions allows determination of the kinetic
energy release distributions which are seen to extend from 0 to 9 eV for
heavy fragments, and up to 14 eV for light ones. The comparison of present
energy thresholds and kinetic energy release with available published data
gives information about states contributing to the observed processes.
Individual contributions for dissociative excitation and dissociative
ionization are determined for each detected product. A complete database
including cross sections and energies is compiled for use in fusion
application. 相似文献
14.
Y. Xiao Y. Su C. M. N. Kumar C. Ritter R. Mittal S. Price J. Perßon Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,82(2):113-121
The physical and structural properties of Fe1.11Te and
Fe1.11Te0.5Se0.5 have been investigated by means of
X-ray and neutron diffraction as well as physical property
measurements. For the Fe1.11Te compound, the structure
distortion from a tetragonal to monoclinic phase takes place at 64 K
accompanied with the onset of antiferromagnetic order upon cooling.
The magnetic structure of the monoclinic phase was confirmed to be
of antiferromagnetic configuration with a propagation vector
k = (1/2, 0, 1/2) based on Rietveld refinement of neutron
powder diffraction data. The structural/magnetic transitions are
also clearly visible in magnetic, electronic and thermodynamic
measurements. For superconducting Fe1.11Te0.5Se0.5
compound, the superconducting transition with T
c
= 13.4 K
is observed in the resistivity and ac susceptibility measurements.
The upper critical field H
c2 is obtained by measuring
the resistivity under different magnetic fields. The Kim’s critical
state model is adopted to analyze the temperature dependence of the
ac susceptibility and the intergranular critical current density is
calculated as a function of both field amplitude and temperature.
Neutron diffraction results show that
Fe1.11Te0.5Se0.5 crystalizes in tetragonal structure
at 300 K as in the parent compound Fe1.11Te and no structural
distortion is detected upon cooling to 2 K. However an anisotropic
thermal expansion anomaly is observed around 100 K. 相似文献
15.
A. V. Malakhovskii S. L. Gnatchenko I. S. Kachur V. G. Piryatinskaya A. L. Sukhachev V. L. Temerov 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(1):1-10
Optical absorption spectra of trigonal crystal TbFe3(BO3)4 have been studied in the region of 7F6 → 5D4 transition in Tb3+ ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb3+ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice,
have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the
absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be
due to the abrupt change of equilibrium geometry of the local Tb3+ ion environment only in the excited state of the Tb3+ ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb3+ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has
been shown that the ground state (in D
3 symmetry approximation) consists of two close singlet states of A
1 and A
2 type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of
the excited electronic states relative to that of the ground state have been
experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines
has been observed in the vicinity of the TbFe3(BO3)4 structural phase transition. The temperature interval of coexistence of the phases is about 3 K. 相似文献
16.
H. Cherkani-Hassani S. Cherkani-Hassani D. S. Belic J. J. Jureta J. Lecointre P. Defrance 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,58(1):75-83
Absolute cross-sections for electron-impact ionization and dissociation of
C2H2+ and C2D2+ have been measured for electron energies
ranging from the corresponding thresholds up to 2.5 keV. The animated
crossed beams experiment has been used. Light as well as heavy fragment ions
that are produced from the ionization and the dissociation of the target
have been detected for the first time. The maximum of the cross-section for
single ionization is found to be (5.56 ± 0.03)× 10-17 cm2 around 140 eV. Cross-sections for dissociation of C2
H2+ (C2D2+) to ionic products are seen to decrease for two orders
of magnitude, from C2D+ (12.6 ± 0.3) × 10-17 cm2 over CH+(9.55 ± 0.06) × 10-17 cm2,
C+ (6.66 ± 0.05) × 10-17 cm2, C2+ (5.36 ± 0.27) × 10-17 cm2, H+ (4.73 ±
0.29) × 10-17 cm2 and CH2+ (4.56 ± 0.27) × 10-18 cm2 to H2+ (5.68 ± 0.49) ×
10-19 cm2. Absolute
cross-sections and threshold energies have been compared with the scarce
data available in the literature. 相似文献
17.
The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd3+ ions in CaNb2O6 crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10−20 cm2 with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd3+ ions in CaNb2O6 crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω
t
are Ω
2=5.321×10−20 cm2,Ω
4=1.734×10−20 cm2,Ω
6=2.889×10−20 cm2. The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β
1=36.03%,β
2=52.29%,β
3=11.15%,β
4=0.533%. The emission cross section at 1062 nm is 9.87×10−20 cm2. 相似文献
18.
T. V. Drokina O. A. Bajukov G. A. Petrakovskiy D. A. Velikanov 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(8):1054-1055
The magnetic properties of a synthesized dielectric NaFeGe2O6. polycrystal have been studied. The antiferromagnetic ordering of this compound below 15 K has been established. The Mössbauer spectrum at 300 K is a quadrupole doublet; it is characterized by an isomeric shift typical of the high-spin Fe3+ ion in the octahedral coordination and quadrupole splitting, which indicates distortion of the oxygen octahedron around the iron cation. Quasi-one-dimensionality of the sample magnetic structure is proved. 相似文献
19.
Tingyin Ning Cong Chen Yueliang Zhou Heng Lu Dongxiang Zhang Hai Ming Guozhen Yang 《Applied Physics A: Materials Science & Processing》2009,94(3):567-570
CaCu3Ti4O12 (CCTO) thin films were successfully prepared on LaAlO3 substrates by pulsed laser deposition technique. We measured the nonlinear optical susceptibility of the thin films using
Z-scan method at a wavelength of 532 nm with pulse durations of 25 ps and 7 ns. The large values of the third-order nonlinear
optical susceptibility, χ
(3), of the CCTO film were obtained to be 2.79×10−8 esu and 3.30×10−6 esu in picosecond and nanosecond time regimes, respectively, which are among the best results of some representative nonlinear
optical materials. The origin of optical nonlinearity of CCTO films was discussed. The results indicate that the CCTO films
on LaAlO3 substrates are promising candidate materials for applications in nonlinear optical devices. 相似文献
20.
H. Cherkani-Hassani D. S. Belic J. J. Jureta J. Lecointre P. Defrance 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,58(1):85-94
Absolute cross-sections for electron-impact dissociative ionization of C2
H2+ and C2 D2+ to CH+, C+, C2+ , H+, CH2+
and C2D+ fragments are determined for electron energies ranging
from the corresponding threshold to 2.5 keV. Results obtained in a crossed
beams experiment are analyzed to estimate the contribution of dissociative
ionization to each fragment formation. The dissociative ionization cross
sections are seen to decrease for more than an order of magnitude, from
CH+ (5.37±0.10) × 10-17 cm2 over C+ (4.19±
0.16) × 10-17 cm2, C2D+ (3.94±0.38) ×
10-17 cm2, C2+ (3.82±0.15) × 10-17 cm2
and H+ (3.37±0.21) × 10-17 cm2 to CH2+
(2.66±0.14) × 10-18 cm2. Kinetic energy release
distributions of fragment ions are also determined from the analysis of the
product velocity distribution. Cross section values, threshold energies and
kinetic energies are compared with the data available from the literature.
Conforming to the scheme used in the study of the dissociative excitation of
C2H2+
( C2 D2+ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in
a format suitable for their implementation in plasma simulation codes. 相似文献