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1.
We report measurements of the temperature dependence of the electrical resistivity, ρ(T), and magnetic pen-etration depth, λ(T), for polycrystalline samples of Eu0.5K0.5Fe2As2 with T
c
= 31 K. ρ(T) follows a linear temperature dependence above T
c
and bends over to a weaker temperature dependence around 150 K. The magnetic penetration depth, determined by radio frequency
technique displays an unusual minimum around 4 K which is associated with short-range ordering of localized Eu3+ moments.
The article is published in the original. 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.
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
4.
M. D. Volnyanskii S. N. Plyaka M. P. Trubitsyn Yahia A. H. Obaidat 《Physics of the Solid State》2012,54(3):499-503
The electrical properties of a lithium heptagermanate (Li2Ge7O15) crystal have been studied in DC and AC measuring fields at temperatures from 500 to 700 K. In a DC field, a substantial
decrease of electrical conductivity σ with time has been detected. On the basis of kinetic dependences σ(t), estimates of the charge carrier diffusion coefficient D have been obtained. In the frequency range 101–105 Hz, the spectra of complex impedance ρ*(f) have been measured. The analysis of diagrams in the complex plane (ρ″–ρ′) has been performed within the equivalent circuit
approach. It has been shown that, in the considered temperature and frequency intervals, the electrical properties of Li2Ge7O15 crystals have been determined by the hopping conduction of interstitial lithium ions A
Li and accumulation of charge carriers near the blocking Pt electrodes. 相似文献
5.
A pronounced step-like (kink) behavior in the temperature dependence of resistivity ρ(T) is observed in the optimally doped Sm1.85Ce0.15CuO4 thin films around T
sf = 87 K and attributed to the manifestation of strong-spin fluctuations induced by Sm3+ moments with the energy ħωsf = k
B
T
sf ≃ 7 meV. The experimental data are found to be well fitted by the residual (zero-temperature) ρres, electron-phonon ρe-ph(T) = AT, and electron-electron ρe-e(T) = BT
2 contributions in addition to the fluctuation-induced contribution ρsf(T) due to thermal broadening effects (of the width ωsf). According to the best fit, the plasmon frequency, impurity scattering rate, electron-phonon coupling constant, and Fermi
energy are estimated as ωp = 2.1 meV, τ
0
−1
= 9.5 × 10−14 s−1, λ = 1.2, and E
F = 0.2 eV, respectively.
The text was submitted by the authors in English. 相似文献
6.
A. Bhattacharyya S. Chatterjee S. Giri S. Majumdar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):347-351
The magnetotransport and magnetic properties of the binary intermetallic compound Ho2In have been investigated. Clear signature of long range ferromagnetic order in the resistivity and the magnetization data
at TC = 85 K is observed. A further spin reorientation type transition is also apparent in our measured data at around Tt = 32 K. The sample exhibits negative magnetoresistance (peak value of –14% at 5 T) over a wide temperature range that extends
well above TC. Substantially large magneto-caloric effect is also observed in the sample (maximum value of –8.5 J kg-1K-1 for 0 → 5 T), which peaks around the TC of the sample. The observed magnetoresistance and magnetocaloric effect are related to the suppression of spin disorder by
an external magnetic field. Ho2In can be an interesting addition to the list of rare-earth based magnetic refrigerant materials showing magneto-caloric effect
across a second order phase transition. 相似文献
7.
Manganese-doped ZnSiAs<Subscript>2</Subscript> chalcopyrite: A new advanced material for spintronics
L.?I.?Koroleva D.?M.?Zashchirinski? T.?M.?Khapaeva S.?F.?Marenkin I.?V.?Fedorchenko R.?Szymczak B.?Krzumanska V.?Dobrovol’ski? L.?Kilanski? 《Physics of the Solid State》2009,51(2):303-308
A new spintronics material with the Curie temperature above room temperature, the ZnSiAs2 chalcopyrite doped with 1 and 2 wt % Mn, is synthesized. The magnetization, electrical resistivity, magnetoresistance, and
the Hall effect of these compositions are studied. The temperature dependence of the electrical resistivity follows a semiconducting
pattern with an activation energy of 0.12–0.38 eV (in the temperature range 124 K ≤ T ≤ 263 K for both compositions). The hole mobility and concentration are 1.33, 2.13 cm2/V s and 2.2 × 1016, 8 × 1016 cm−3 at T = 293 K for the 1 and 2 wt % Mn compositions, respectively. The magnetoresistance of both compositions, including the region
of the Curie point, does not exceed 0.4%. The temperature dependence of the magnetization M(T) of both compositions exhibits a complicated character; indeed, for T ≤ 15 K, it is characteristic of superparamagnets, while for T > 15 K, spontaneous magnetization appears which correspond to a decreased magnetic moment per formula unit as compared to
that which would be observed upon complete ferromagnetic ordering of Mn2+ spins or antiferromagnetic ordering of spins of the Mn2+ and Mn3+ ions. Thus, for T > 15 K, it is a frustrated ferro- or ferrimagnet. It is found that, unlike the conventional superparamagnets, the cluster
moment μ
c
in these compositions depends on the magnetic field: ∼12000–20000μB for H = 0.1 kOe, ∼52–55μB for H = 11 kOe, and ∼8.6–11.0μB at H = 50 kOe for the compositions with 1 and 2 wt % Mn, respectively. The specific features of the magnetic properties are explained
by the competition between the carrier-mediated exchange and superexchange interactions. 相似文献
8.
V. V. Popov P. P. Konstantinov Yu. V. Rud’ 《Journal of Experimental and Theoretical Physics》2011,113(4):683-691
Electrical resistivity ρ and Hal coefficient R are measured as a function of the temperature (T = 1.7−310 K) and the magnetic field (up to H = 28 kOe) in zero-gap semiconductor CuFeS2 samples subjected to hydrostatic compression and under various heat-treatment conditions. At low temperatures, anomalies
are observed in the kinetic effects related to the presence of ferromagnetic clusters: the magnetoresistance at T = 4.2 K and T = 20.4 K acquires a hysteretic character and thermopower α changes its sign at T < 15 K. The temperature dependence of conduction-electron concentration n in CuFeS2 has a power form in the temperature range T = 14−300 K, which is characteristic of the intrinsic conductivity in zero-gap semiconductors. In CuFeS2, we have n(T) ∝ T
1.2; in isoelectron compound Cu1.13Fe1.22Te2, we have n(T) ∝ T
1.93. Heat treatment is found to affect the intrinsic conductivity of CuFeS2, as the action of hydrostatic compression (carrier concentration changes); that is, the carrier concentration changes. However,
a power form of the n(T) and ρ(T) dependences is retained. 相似文献
9.
A. Yu. Mollaev I. K. Kamilov R. K. Arslanov T. R. Arslanov U. Z. Zalibekov V. M. Novotortsev S. F. Marenkin 《JETP Letters》2010,91(9):478-480
The magnetic susceptibility χ/χ0 and the longitudinal Δρ
zz
/ρ0 and transverse Δρ
xx
/ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T
c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has
been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and
magnetoresistance. 相似文献
10.
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
11.
L.?Ya?Vinnikov D.?é.?Bo?nagrov V.?N.?Zverev I.?S.?Veshchunov J.?Karpinski 《Journal of Experimental and Theoretical Physics》2009,109(2):280-285
The vortex lattice of the YBa2Cu4O8 high-temperature superconductor is studied in the basal plane of monocrystalline samples using the decoration technique in
a field interval of 40–600 Oe. Vortex lattice anisotropy (field-independent “compression” of a regular hexagonal vortex cell
in the poorly conducting direction by a factor of about 1.3) is detected. Resistivity anisotropy ρ
a
/ρ
b
measured at temperatures from T
c
to room temperature is 16–9. Possible reasons for the discrepancy between our results and the available data are discussed. 相似文献
12.
A. Kh. Matiev A. N. Georgobiani V. V. Kodin M. A. Matiev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(9):1326-1328
The electrical conductivity and magnetoresistance effect of n and p types of CuInSe2 single crystals were studied within the temperature range of 4.2–300 K and within magnetic fields of up to 6 T. It was found
that the hopping mechanism of conductivity dominates in the temperature range of 4.2–100 K. A peculiarity of electrical conductivity
behavior, accompanied by a change in the magnetoresistance sign in the vicinity of T ≈ 60 K, was revealed. 相似文献
13.
We present the results a study of structure by neutron diffraction and data on the magnetic properties (linear and nonlinear
(second and third order) susceptibilities) of polycrystalline La0.88MnO2.95. This compound exhibits an insulator-metal (IM) phase transition at T
IM
≈ 253 K (above the Curie temperature, T
C
≈ 244 K) and reveals colossal magnetoresistance. The crystal structure is found to be rhombohedral, and the space group is
R3c. Analysis of magnetic properties shows that at T* ≈ 258 K > T
C
, isolated paramagnetic clusters occur in the paramagnetic matrix; their concentration increases upon cooling. We observed
no noticeable differences between the temperature evolution of the clustered state of this manganite with its insulator-metal
transition and in the insulator La0.88MnO2.91. Possible scenarios of the paramagnet-ferromagnet and I-M transitions in a self-organized clustered structure are discussed. 相似文献
14.
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
15.
The temperature behavior of I-U curves and the field and temperature dependences of the electrical resistivity and dielectric permittivity of crystals of the LiCu2O2 phase have been studied. It was established that the crystals belong to p-type semiconductors and that their static resistivity in the range 80–260 K follows the Mott law ρ=Aexp(T0/T)1/4 describing variable-range hopping over localized states. At comparatively low electric fields, the crystals exhibit threshold switching and characteristic S-shaped I-U curves containing a region of negative differential resistivity. In the critical voltage region, jumps in the conductivity and dielectric permittivity are observed. Possible mechanisms of the disorder and electrical instability in these crystals are discussed. 相似文献
16.
A. V. Malakhovskii E. V. Eremin D. A. Velikanov A. V. Kartashev A. D. Vasil’ev I. A. Gudim 《Physics of the Solid State》2011,53(10):2032-2037
The magnetic properties of the Nd0.5Gd0.5Fe3(BO3)4 single crystal have been studied in principal crystallographic directions in magnetic fields to 90 kG in the temperature
range 2–300 K; in addition, the heat capacity has been measured in the range 2–300 K. It has been found that, below the Néel
temperature T
N = 32 K down to 2 K, the single crystal exhibits an easy-plane antiferromagnetic structure. A hysteresis has been detected
during magnetization of the crystal in the easy plane in fields of 1.0–3.5 kG, and a singularity has been found in the temperature
dependence of the magnetic susceptibility in the easy plane at a temperature of 11 K in fields B < 1 kG. It has been shown that the singularity is due to appearance of the hysteresis. The origin of the magnetic properties
of the crystal near the hysteresis has been discussed. 相似文献
17.
M. Putti E. Galleani d'Agliano D. Marrè F. Napoli M. Tassisto P. Manfrinetti A. Palenzona C. Rizzuto S. Massidda 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):439-443
We report measurements of the resistivity, ρ, and the Seebeck coefficient, S
, of a MgB2 sintered sample, and compare S with theoretical calculations based on precise electronic structure calculations. ρ is fitted well by a generalized Bloch-Grüneisen equation with a Debye temperature Θ
R
of 1050 K. S is given by the sum of a diffusive and a phonon drag term and the behavior in the temperature region T
c
<
T
< 0.1Θ
R
follows the relationship AT+BT3. The phonon drag term indicates a strong electron-phonon interaction. The diffusive term, compared with calculations, suggests
that σ bands give the main contribution to the Seebeck effect.
Received 16 November 2001 and Received in final form 21 December 2001 相似文献
18.
G. Li S.-J. Feng F. Liu Y. Yang R.-K. Zheng T. Qian X.-Y. Guo X.-G. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):5-11
The magnetic transport properties have been measured for La0.67-xYxCa0.33MnO3 ( 0 ⩽
x
⩽ 0.14) system. It was found that the transition temperature T
p
almost linearly moves to higher temperature as H increases. Electron spin resonance confirms that above T
p
, there exist ferromagnetic clusters. From the magnetic polaron point of view, the shift of T
p
vs. H was understood, and it was estimated that the size of the magnetic polaron is of 9.7 ∼ 15.4 ? which is consistent with the magnetic correlation length revealed by the small-angle neutron-scattering technique. The
transport properties at temperatures higher than T
p
conform to the variable-range hopping mechanism.
Received 27 August 2002 / Received in final form 2 December 2002 Published online 14 March 2003 相似文献
19.
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
20.
We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa2Se4:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm
is due to intracenter transitions 4f6 5d–4f7 (8S7/2) of the Eu2+ ions. From the temperature dependence of the intensity (log I–103/T), we determined the activation energy (E
a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths:
0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu2+ ions in the CaGa2Se4 crystal found from the luminescence decay kinetics is 3.8 μsec.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009. 相似文献