共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
M. Patra K. De S. Majumdar S. Giri 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):367-371
We observe the negative shift of the magnetic hysteresis loop at 5 K, while the sample is cooled in external magnetic field
in case of 30% of Fe substitution in LaMnO3. The negative shift and training effect of the hysteresis loops indicate the phenomenon of exchange bias. The cooling field
dependence of the negative shift increases with the cooling field below 7.0 kOe and then, decreases with further increase
of cooling field. The temperature dependence of the negative shift of the hysteresis loops exhibits that the negative shift
decreases sharply with increasing temperature and vanishes above 20 K. Temperature dependence of dc magnetization and ac susceptibility
measurements show a sharp peak (Tp) at 51 K and a shoulder (Tf) around 20 K. The relaxation of magnetization shows the ferromagnetic and glassy magnetic components in the relaxation process,
which is in consistent with the cluster-glass compound. 相似文献
4.
C. Ravi Dhas R. Venkatesh R. Sivakumar A. Moses Ezhil Raj C. Sanjeeviraja 《Ionics》2016,22(10):1911-1926
Electrochromic effect of cobalt oxide thin films was studied as a function of substrate temperature (573–673 K). Tricobalt tetraoxide (Co3O4) thin films were deposited on glass and fluorine-doped tin oxide (FTO) substrates by nebulized spray technique using cobalt nitrate as precursor material. The XRD patterns indicated (311) plane was dominant for all the films irrespective of the deposition temperature. Williamson-Hall (W-H) analysis was made to understand the strain variation in the prepared Co3O4 films under different deposition temperature by employing uniform deformation model (UDM). Scanning electron microscopy images revealed porous morphology for the film prepared at 623 K. The optical parameters such as refractive index (n), extinction coefficient (k), and band gap were derived from UV-visible spectra of Co3O4 films. The electrochromic performance of the deposited Co3O4 films was analyzed through cyclic voltammetry, chronocoulometry, chronoamperometry, and iono-optical studies. 相似文献
5.
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
6.
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
7.
X.T. Li P.Y. Du H. Ye C.L. Mak K.H. Wong 《Applied Physics A: Materials Science & Processing》2008,92(2):397-400
Textured LixNi2-xO (LNO) thin films have been fabricated on (001)MgO substrates by pulsed laser deposition technique. The as-deposited LNO
films shows a conductivity of 2.5×10-3 Ω m and possess a transmittance of about 35% in the visible region. Subsequent deposition of Sr0.6Ba0.4Nb2O6 (SBN60) thin film on these LNO-coated MgO substrates resulted in a textured SBN layer with a 〈001〉 orientation perpendicular
to the substrate plane. Phi scans on the (221) plane of the SBN layer indicated that the films have two in-plane orientations
with respect to the substrate. The SBN unit cells were rotated in the plane of the film by ± 8.2° as well as ± 45° with respect
to the LNO/MgO substrate. Besides the highly (00l)-orientation, the SBN films also exhibited a dense microstructure as shown
by scanning electron microscopy. The electro-optic coefficient (r33) of the SBN film was measured to be 186 pm/V. On the basis of our results, we have demonstrated that the LNO film can be
used as a buffer layer as well as a transparent bottom electrode for waveguide applications. The SBN/LNO heterostructure is
also a suitable candidate for integrated electro-optics devices.
PACS 42.79.Gn; 42.82.Et; 78.20.Ci 相似文献
8.
L. S. Uspenskaya I. V. Kurbatova G. Nurgaliev S. Miteva 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(8):1110-1112
The kinetics of magnetization reversal of a thin LSMO film has been studied for the first time. It is shown that the magnetic
domain structure critically depends on the conditions of structure formation. In the demagnetized state (after zero-field
cooling from T
c
), a maze-like domain microstructure with perpendicular magnetization is formed in the film. However, after field cooling
and/or saturating magnetization by a field of arbitrary orientation, the [110] direction of spontaneous magnetization in the
film plane is stabilized; this pattern corresponds to macrodomains with in-plane magnetization. Further film magnetization
reversal (both quasi-static and pulsed) from this state is implemented via nucleation and motion of 180° “head-to-head” domain
walls. Upon pulse magnetization reversal, the walls “jump” at a distance proportional to the applied field strength and then
undergo thermally activated drift. All dynamic characterisitcs critically depend on the temperature when the latter varies
around the room temperature. 相似文献
9.
F. Wu X.M. Li W.D. Yu X.D. Gao X. Zhang 《Applied Physics A: Materials Science & Processing》2007,88(4):781-784
Thin films of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN-PT) have been grown on Ir/MgO buffered Si(100) substrates at different substrate temperatures by pulsed laser deposition.
Crystalline phases as well as preferred orientations in the PMN-PT films were investigated by X-ray diffraction analysis (XRD).
The microstructure, dielectric and ferroelectric properties of PMN-PT film prepared at 650 °C were studied. The results show
that the film prepared at 650 °C exhibits pure perovskite phase and single c-axis orientation. The dielectric constant and
dissipation factor of the single c-axis oriented film are 1000 and 0.04 at a frequency of 1 kHz, while the remnant polarization
and coercive field are about 13.0 μC/cm2 and 100 kV/cm under an electric field of 480 kV/cm, respectively.
PACS 81.15.Fg; 77.80.-e; 77. 22.Ej; 77.55.+f; 85.50.Gk 相似文献
10.
E. Govea-Alcaide I. García-Fornaris P. Muné R. F. Jardim 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):373-378
Measurements of the electrical resistivity as a function
of temperature, ρ(T), for different values of applied
magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in
polycrystalline samples of Bi1.65Pb0.35Sr2Ca2
Cu3O10+δ subjected to different uniaxial compacting
pressure (UCP). We have found appreciable differences in the grain
orientation between samples by using X-ray diffractometry. From
the X-ray diffraction patterns performed, in powder and pellet
samples, we have estimated the Lotgering factor along the (00l)
direction, F(00l). The results indicate that F(00l)
increases ~23% with increasing UCP suggesting that grains
of these samples are preferentially aligned along the c-axis,
which is parallel to the compacting direction. The resistive
transition of the samples have been interpreted in terms of the
thermally activated flux-creep model. In addition, the effective
intergranular pinning energy, U0, have been determined for
different applied magnetic field. The magnetic field dependence of
U0, for Ba > 8 mT, was found to follow a H- α
dependence with α = 0.5 for all samples. The analysis of the
experimental data strongly suggested that increasing UCP results
in appreciable changes in both the grain alignment and the grain
connectivity of the samples. We have successfully interpreted the
data by considering the existence of three different
superconducting levels within the samples: the superconducting
grains, the weak-links, and the superconducting clusters. 相似文献
11.
Xiao-Ping Shen Hua-Juan Miao Hui Zhao Zheng Xu 《Applied Physics A: Materials Science & Processing》2008,91(1):47-51
Well-aligned Co3O4 nanotubes were synthesized within the nanochannels of porous anodic alumina membranes using a single-source chemical vapor
deposition method. Scanning electron microscopy and transmission electron microscopy showed that the Co3O4 nanotubes are highly ordered with uniform diameter in the range of 100–300 nm and length up to tens of microns. X-ray diffraction,
the Raman spectrum, energy-dispersive spectroscopy and selected-area electron diffraction demonstrated that the nanotubes
are composed of pure cubic phase polycrystalline Co3O4. Magnetic measurements using a SQUID magnetometer suggested the presence of a strong antiferromagnetic interaction with Weiss
constant θ= -248 K. The real and imaginary parts of the ac susceptibility at f= 10 Hz had a maximum at 4.0 K, and the field
dependence of the magnetization at 1.8 K showed a small hysteresis loop with a coercivity of ∼ 98 Oe.
PACS 81.07.De; 81.15.Gh; 78.30.-j; 75.75.+a; 61.46.Np 相似文献
12.
40-to 120-nm-thick (001)La0.67Ca0.33MnO3 films grown through laser evaporation on (001)NdGaO3 were studied. The lattice parameters of the La0.67Ca0.33MnO3 films measured in the substrate plane (a∥=3.851 Å) and along the normal to its surface (a⊥=3.850 Å) practically coincided with that of the pseudocubic neodymium gallate. The unit-cell volume of the La0.67Ca0.33MnO3 film was slightly smaller than that of stoichiometric bulk samples. The position of the maximum in the temperature dependence of electrical resistivity did not depend on the thickness of the La0.67Ca0.33MnO3 film. The negative magnetoresistance (MR≈?0.25, H=0.4 T) of La0.67Ca0.33MnO3 films reached a maximum at 239–244 K. 相似文献
13.
H. He W. Y. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):457-463
The spin-states of cobalt based perovskite compounds depend sensitively
on the valence state and local crystal environment of Co ions and the
rich physical properties arise from strong coupling among charge, spin,
and orbital degrees of freedom. While extensive studies have been carried
out in the past, most of them concentrated on the isotropic compound
LaCoO3. In this paper, using the unrestricted Hartree-Fock approximation
and the real-space recursion method, we have investigated the competition
of various magnetically ordered spin-states of anisotropic double-layered
perovskite Sr2Y0.5Ca0.5Co2O7. The energy
comparison among these states shows that the nearest-neighbor
high-spin-intermediate-spin ferromagnetically ordered state is the relevant
magnetic ground state of the compound. The magnetic structure and sizes of
magnetic moments are consistent with the recent experimental observation. 相似文献
14.
Y. B. Qin H. X. Yang L. Wang H. F. Tian C. Ma Y. Li H. L. Shi J. Q. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(2):231-236
The structural and physical properties of the layered
Yb2Fe3O7 have been extensively investigated. Transmission
electron microscopy (TEM) observations at room temperature reveal the
presence of diffuse zigzag-type streaks at 1/3(h h l) running along the c*
axis direction, suggesting the presence of a charge ordered state with a
shorter coherence length in comparison with that in Lu2Fe3O7.
The measurements of magnetization demonstrate that the replacement of
Lu3+ by the magnetic Yb3+ ion in this layered system could
result in visible effects on the low-temperature magnetic properties: the
ferrimagnetic phase transition temperature decreases and an additional
magnetic anomaly possibly attributed to antiferromagnetic coupling between
Yb and Fe layers appears at around 50 K. Analysis of the dielectric
properties shows that the Yb2Fe3O7 material in general has a
large dielectric constant of about 5000 at room temperature, and a broader
relaxation time distribution in comparison with ErFe2O4. 相似文献
15.
V. P. Dyakonov R. Szymczak A. D. Prokhorov E. Zubov A. A. Prokhorov G. Petrakovskii L. Bezmaternikh M. Berkowski V. Varyukhin H. Szymczak 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(3):291-298
Magnetic and electron paramagnetic resonance (EPR) properties of
EuFe3(BO3)4 single crystals have been studied over the
temperature range of 300–4.2 K and in a magnetic field up to 5 T. The
temperature, field and orientation dependences of susceptibility,
magnetization and EPR spectra are presented. An antiferromagnetic ordering
of the Fe subsystem occurs at about 37 K. The easy direction of
magnetization perpendicular to the c axis is determined by magnetic
measurements. Below 10 K, we observe an increase of susceptibility connected
with the polarization of the Eu sublattice by an effective exchange field of
the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the
c axis, we have observed an increase of magnetization at T < 10 K in the
applied magnetic field, which can be attributed to the appearance of the
magnetic moment induced by the magnetic field applied in the basal plane.
According to EPR measurements, the distance between the maximum and minimum
of derivative of absorption line of the Lorentz type is equal to 319 Gs. The
anisotropy of g-factor and linewidth is due to the influence of crystalline
field of trigonal symmetry. The peculiarities of temperature dependence of
both intensity and linewidth are caused by the influence of excited states
of europium ion (Eu3+). It is supposed that the difference between the
g-factors from EPR and the magnetic measurements is caused by exchange
interaction between rare earth and Fe subsystems via anomalous Zeeman
effect. 相似文献
16.
G. A. Politova I. S. Tereshina G. S. Burkhanov O. D. Chistyakov V. B. Chzhan V. I. Nizhankovskii A. Zaleski T. P. Kaminskaya V. V. Popov 《Physics of the Solid State》2011,53(10):2028-2031
A complex investigation of the structural, magnetic, and magnetothermal properties of the Tb0.3Dy0.7Co2 compound synthesized with the use of high-purity rare-earth metals has been performed. The phase composition has been controlled
using the X-ray structural analysis, and the topology of the alloy surface has been investigated using atomic-force microscopy.
It has been established that the Tb0.3Dy0.7Co2 compound is single-phase, while the samples selected for measurements possess a clearly pronounced texture. The magnetization
has been measured using a vibrating-sample magnetometer in the fields up to 100 kOe in a temperature range from 4.2 to 200
K. The Curie temperature of the compound is 170 K. The data on the temperature dependence of heat capacity of Tb0.3Dy0.7Co2 have been obtained. The magnetocaloric effect ΔT has been measured by a direct method in the fields up to 18 kOe applied both along and perpendicularly to the texture axis.
The anisotropic behavior of the magnitude ΔT for this compound, which possesses the cubic structure, has been found. The maximum value of the magnetocaloric effect ΔT = 2.3 K (ΔH = 18 kOe) has been observed upon applying the magnetic field along the texture axis. 相似文献
17.
N. B. Ivanova N. V. Kazak Yu. V. Knyazev D. A. Velikanov L. N. Bezmaternykh S. G. Ovchinnikov A. D. Vasiliev M. S. Platunov J. Bartolomé G. S. Patrin 《Journal of Experimental and Theoretical Physics》2011,113(6):1015-1024
Co3O2BO3 and Co2FeO2BO3 single crystals with a ludwigite structure are fabricated, and their crystal structure and magnetic properties are studied
in detail. Substituted ludwigite Co2FeO2BO3 undergoes two-stage magnetic ordering at the temperatures characteristic of Fe3O2BO3 (T
N1 ≈ 110 K, T
N2 ≈ 70 K) rather than Co3O2BO3 (T
N
= 42 K). This effect is explained in terms of preferred occupation of nonequivalent crystallographic positions by iron, which
was detected by X-ray diffraction. Both materials exhibit a pronounced uniaxial magnetic anisotropy. Crystallographic direction
b is an easy magnetization axis. Upon iron substitution, the cobalt ludwigite acquires a very high magnetic hardness. 相似文献
18.
D. Do S. S. Kim S. W. Yi J. W. Kim 《Applied Physics A: Materials Science & Processing》2009,94(3):697-701
Ferroelectric and dielectric properties of bilayered ferroelectric thin films, SrBi4Ti4O15 grown on Bi4Ti3O12, were investigated. The thin films were annealed at 700°C under oxygen atmosphere. The bilayered thin films were prepared
on a Pt(111)/Ti/SiO2/Si substrate by a chemical solution deposition method. The dielectric constant and dielectric loss of the bilayered thin
films were 645 and 0.09, respectively, at 100 kHz. The value of remnant polarization (2P
r) measured from the ferroelectric thin film capacitors was 60.5 μC/cm2 at electric field of 200 kV/cm. The remnant polarization was reduced by 22% of the initial value after 1010 switching cycles. The results showed that the ferroelectric and dielectric properties of the SrBi4Ti4O15 on Bi4Ti3O12 ferroelectric thin films were better than those of the SrBi4Ti4O15 grown on a Pt-coated Si substrate suggesting that the improved properties may be due to the different nucleation and growth
kinetics of SrBi4Ti4O15 on the c-axis-oriented Bi4Ti3O12 layer or on the Pt-coated Si substrate. 相似文献
19.
J.-E. Jørgensen L. Keller 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):445-453
The crystal and magnetic structures of
Dy1-xCaxBaCo2O5.5
for x = 0.0 and 0.1 have been studied by neutron powder diffraction and the
crystal structures of both compounds were found to be best described in
space group Pmmm with a ap × 2ap × 2ap unit cells where ap is the lattice parameter
of the cubic perovskite unit cell. The a- and b-axes were found to decrease
and increase abruptly between 315 and 350 K as the temperature
increases and the unit cell volumes exhibit signs of excess thermal
expansion in the temperature range from 260 to 315 K.
Dy0.9Ca0.1BaCo2O5.5
orders antiferromagnetically for T ≤ 305 K into a G-type magnetic
structure with a 2ap × 2ap × 2ap
magnetic unit cell. DyBaCo2O5.5 exhibits two
magnetically ordered phases and a G-type magnetic structure was observed at
the investigated temperatures 260 and 290 K. A 2ap ×
2ap × 4ap magnetic unit cell was needed for
indexing of the magnetic reflections observed for T ≤ 230 K. The
low temperature magnetic structure of
DyBaCo2O5.5 is different from the observed
magnetic structures of TbBaCo2O5.5 and
HoBaCo2O5.5 despite the proximity of Tb, Dy and
Ho in the periodic table. It is a relatively complex antiferromagnetic
structure with both pyramidally and octahedrally coordinated Co ions in the
intermediate spin state. It contains both ferro- and antiferromagnetic
interactions and the magnetic moments are canted in the
a, b-plane. The canting
angles between the magnetic moments and the
b-axis are 6.6 and 50.0° at 20 K for the
pyramidally and octahedrally coordinated Co ions, respectively. The high and
low temperature magnetic phases were found to coexist at 230 K. 相似文献
20.
Dinesh Pathak R. K. Bedi Davinder Kaur 《Applied Physics A: Materials Science & Processing》2009,95(3):843-847
AgInSe2 films were prepared by a thermal evaporation technique onto Si(100) substrates at a pressure of 10−5 mbar. Structural and optical properties of films deposited at 300 and 473 K have been investigated. The film composition
was studied by energy dispersive analysis through X-rays. X-ray diffraction patterns indicate that AgInSe2 films have chalcopyrite structure with strong preferred orientation in the (112) direction. Average vertical crystallite
size of 25 nm was observed. The optical energy gaps of 1.20 and 1.90 eV were obtained due to the fundamental absorption edge
and a transition originating from crystal field splitting, respectively. Field emission scanning electron microscopy shows
loosely packed grains of spherical symmetry with some facets. 相似文献