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1.
New doped manganite multiferroics Tb0.95Bi0.05MnO3, Gd0.75Ce0.25Mn2O5, and Eu0.8Ce0.2Mn2O5, which are semiconductors, have been grown and studied. The starting dielectric multiferroics TbMnO3 and RMn2O5 (R = Gd and Eu) have close magnetic and ferroelectric ordering temperatures of 30–40 K. The crystals studied are multiferroics
in which states with giant permittivity and ferromagnetism coexist at room temperature. An analysis of the dielectric properties
suggests that, at temperatures T ≥ 180 K, these crystals undergo a phase separation involving dynamic periodic alternation of quasi-2D layers of mixed-valence
manganese ions, a process accounting for the onset of charge-induced ferroelectricity. At low temperatures (T < 100 K), a small phase volume in the crystals is occupied by as-grown quasi-2D layers containing dopants and carriers. Most
of the crystal volume is occupied by the carrier-free dielectric phase. Thermally activated hopping conduction involving carrier
self-organization in the crystal matrix with ferroelectric frustrations drives a phase transition to the state of charge-induced
ferroelectricity at T ∼ 180 K.
Original Russian Text ? V.A. Sanina, E.I. Golovenchits, V.G. Zalesskiĭ, 2008, published in Fizika Tverdogo Tela, 2008, Vol.
50, No. 5, pp. 874–882. 相似文献
2.
3.
A. M. Kuz’menko A. A. Mukhin V. Yu. Ivanov A. M. Kadomtseva S. P. Lebedev L. N. Bezmaternykh 《Journal of Experimental and Theoretical Physics》2011,113(1):113-120
The magnetoresonance and dielectric properties of a number of crystals of a new family of multiferroics, namely, rare-earth
ferroborates RFe3(BO3)4 (R = Y, Eu, Pr, Tb, Tb0.25Er0.75), are studied in the sub-millimeter frequency range (ν = 3–20 cm−1). Ferroborates with R = Y, Tb, and Eu exhibit permittivity jumps at temperatures of 375, 198, and 58 K, respectively, which
are caused by the R32 → P3121 phase transition. Antiferromagnetic resonance (AFMR) modes in the subsystem of Fe3+ ions are detected in the range of anti-ferromagnetic ordering (T < T
N
= 30–40 K) in all ferroborates that have either an easy-plane (Y, Eu) or easy-axis (Pr, Tb, Tb0.25Er0.75) magnetic structure. The AFMR frequencies are found to depend strongly on the magnetic anisotropy of a rare-earth ion and
its exchange interaction with the Fe subsystem, which determine the type of magnetic structure and the sign and magnitude
of an effective anisotropy constant. The basic parameters of the magnetic interactions in these ferroborates are found, and
the magnetoelectric contribution to AFMR is analyzed. 相似文献
4.
T. V. Panchenko 《Physics of the Solid State》1997,39(7):1085-1090
Anomalies of the dielectric properties of undoped and aluminum-and gallium-doped crystals of Bi12SiO20 are investigated in the frequency and temperature range ν=102–108 Hz and T=300–800 K. They are shown to be due to Debye relaxation processes and determined by the relaxor parameters. The mechanism
of electron thermal polarization is discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 1223–1229 (July 1997) 相似文献
5.
G. A. Petrakovskii K. A. Sablina A. M. Vorotynov O. A. Bayukov A. F. Bovina G. V. Bondarenko R. Szymczak M. Baran H. Szymczak 《Physics of the Solid State》1999,41(4):610-612
The temperature dependence of the magnetic susceptibility of Cu3B2O6 single crystals grown by spontaneous crystallization from a melt consisting of a mixture of CuO and B2O3 and the behavior of their magnetization are investigated in magnetic fields up to 55 kOe. A broad susceptibility maximum
is observed near 39 K, and a sharp drop in susceptibility is observed at T<10 K. The paramagnetic Néel temperatures for all orientations of the magnetic field in the crystal investigated are negative,
attesting to the predominantly antiferromagnetic character of the exchange interactions. The effective magnetic moment of
the Cu2+ ion is anisotropic and lies in the range from 1.054μ
B to 1.545μ
B. The magnetization depends linearly on magnetic field at T>10 K, whereas at temperatures below 10 K a discontinuity is observed at fields of the order of 40 kOe. At room temperature,
electron magnetic resonance characterized by an almost isotropic g factor (g=2.165) is detected at 36.22 GHz. The exchange interactions in Cu3B2O6 are analyzed on the basis of the Goodenough-Kanamori rules. The possibility of the establishment of a singlet magnetic state
in the crystal is analyzed.
Fiz. Tverd. Tela (St. Petersburg) 41, 677–679 (April 1999) 相似文献
6.
V. Yu. Ivanov A. A. Mukhin A. S. Prokhorov A. M. Balbashov L. D. Iskhakova 《JETP Letters》2010,91(8):392-397
The transition from a stable orthorhombic structure to a hexagonal structure has been revealed in Tb1−x
Y
x
MnO3 multiferroics at x = 0.2–0.4. It has been shown that almost single-phase crystals with an orthorhombic or hexagonal structure can be obtained
by choosing the growth conditions. It has been found that the magnetic and dielectric properties of orthorhombic single crystals
with x = 0.2–0.3 are similar to the properties of pure TbMnO3 and are characterized by a strong anisotropy of the magnetic susceptibility at low temperatures and by the presence of a
number of magnetic phase transitions, including those to the ferroelectric state. New spontaneous (T ≤ 15 K) and magnetic-field induced (H | C
6) phase transitions accompanied by the appearance of an uncompensated rare-earth magnetic moment ∼1 μB/mole have been observed in hexagonal single crystals with x = 0.3–0.5. 相似文献
7.
The magnetic properties of complex oxides Ln
2Mn2/3Mo4/3O7 (Ln=Sm, Gd, Tb, or Y) with a pyrochlore-type structure are studied in the temperature range 2–300 K. For all compounds in the
paramagnetic state, the temperature dependence of the magnetic susceptibility is described by a generalized Curie-Weiss law
with a temperature-independent component of ∼10−6 cm3/g and with a Weiss constant Θ<0 and |Θ|<16 K. At low temperatures (T<10–12 K), the compounds have spin-glass properties; they exhibit magnetic and temperature hysteresis and the typical dependences
of the imaginary and real parts of the dynamic magnetic susceptibility on temperature and the frequency of an ac magnetic
field in a wide range of magnetization relaxation times. The data obtained suggest that d electrons are responsible for the formation of frustrated exchange interactions in the compounds and that 4f electrons in the compounds with Sm or Tb provide strong magnetic-anisotropy effects.
__________
Translated from Fizika Tverdogo Tela, Vol. 46, No. 2, 2004, pp. 287–295.
Original Russian Text Copyright ? 2004 by Korolev, Bazuev. 相似文献
8.
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
9.
S. I. Vorob’ev E. I. Golovenchits V. P. Koptev E. N. Komarov S. A. Kotov V. A. Sanina G. V. Shcherbakov 《JETP Letters》2010,91(10):512-517
The magnetic properties of the EuMn2O5 multiferroic (samples consisting of single crystals and ceramic samples) have been investigated by the muon-spin-relaxation
(μSR) method in the temperature range of 10–300 K. Below the magnetic ordering temperature T
N = 40 K, the loss of the polarization of muons and the effect of the external magnetic field have been observed. Both phenomena
can be explained by an additional channel of the depolarization of muons owing to the appearance of muons in a medium with
a low electron density due to the charge separation process (the redistribution of the electron density in the phase transition
process). The “memory” phenomenon has been revealed in a sample in the external magnetic field; the memory relaxation time
depends on the size of the structure units of the samples (single crystals or ceramic grains). 相似文献
10.
V. P. D’yakonov V. I. Markovich V. L. Kovarskii A. V. Markovich M. Borowiec A. Jendrzejczak H. Szymczak 《Physics of the Solid State》1999,41(3):440-444
The investigation of the specific heat of a RbDy(WO4)2 single crystal at temperatures 0.2–2.5 K and in magnetic fields up to 2 T are reported. The temperature dependence of the
specific heat near T
N=0.818 K is compared with the predictions for different models. The 2D Ising model describes satisfactorily C(T) below T
N, while for T>T
N none of the theoretical models agree with the behavior of C(T) of RbDy(WO4)2. The H-T phase diagram for H∥c is complicated and possesses a triple point, where regions of existence of three magnetic phases converge. The magnetic ordering
is analyzed from the standpoint of the Jahn-Teller nature of the structural phase transitions occurring in RbDy(WO4)2 at higher temperatures. It is shown that the form of the phase diagram depends on the direction of the vector H, for the general case of an arbitrary direction of H, two phase transitions can occur with increasing field.
Fiz. Tverd. Tela (St. Petersburg) 41, 491–496 (March 1999) 相似文献
11.
B. I. Belevtsev V. B. Krasovitsky D. G. Naugle K. D. D. Rathnayaka Glenn Agnolet I. Felner 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1049-1052
Magnetic and superconducting properties of polycrystalline samples of RuSr2Gd1.5Ce0.5Cu2O(10 − δ), asprepared (by solid-state reaction) and annealed in pure oxygen at different pressure are presented. Specific heat and
magnetization were investigated in the temperature range 1.8–300 K with a magnetic field up to 8 T. Specific heat, C (T), shows a jump at the superconducting transition (with onset at T ≈ 37.5 K) and a Schottky-type anomaly below 20 K. It is found that curves C(T) taken for different values of magnetic field have the same crossing point (at T
* ≈ 2.7 K) for all samples studied. At the same time, C(H) curves taken for different temperatures have a crossing point at a characteristic field H
* ≈ 3.7 T. These effects are manifestations of the crossing-point phenomenon, which is supposed to be inherent for strongly
correlated electron systems. 相似文献
12.
The behavior of the thermal conductivity k(T) of bulk faceted fullerite C60 crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C60, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal
increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon
mean free path λ
p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable
to the lattice constant of the crystal λ
p∼d=1.4 nm at temperatures T>200 K and reaches values λp∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic
phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the
Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the
sample.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997) 相似文献
13.
Yu. F. Popov A. M. Kadomtseva G. P. Vorob’ev V. A. Timofeeva D. M. Ustinin A. K. Zvezdin M. M. Tegeranchi 《Journal of Experimental and Theoretical Physics》1998,87(1):146-151
The field dependence of the magnetoelectric effect and longitudinal magnetostriction of Ga2−x
FexO3 single crystals is studied in magnetic fields up to 200 kOe in the temperature range from 4.2 to 300 K. It is shown that
the magnetoelectric effect in these materials is determined mainly by the toroidal moment T and is not related to magnetostriction, as was previously theorized. A new method for determining the toroidal moment by
measuring the electric polarization in a strong magnetic field is proposed. The value of the toroidal moment of the unit cell
in Ga1.15Fe0.85O3 is calculated: T=(T
a
,0,0), where T
a
=24.155μ
B
Å per unit cell. Experimental data are analyzed using a theory of toroidal spin ordering, which gives good agreement with
experiment.
Zh. éksp. Teor. Fiz. 114, 263–272 (July 1998)
Deceased. 相似文献
14.
The magnetic properties of Y2
B
2/3Mo4/3O7 complex oxides (B = Co, Fe) were studied in the temperature range 2–300 K. At low temperatures, these compounds exhibit spin-glass properties
with freezing temperatures T
f=26 and 33 K, respectively, and typical features in the magnetic hysteresis and in the dependences of the real part of the
dynamic magnetic susceptibility on temperature and ac magnetic field frequency. Above T
f, the static magnetic susceptibility of the samples studied depends on the applied magnetic field, which is tentatively assigned
to the presence of metallic cobalt and/or yttrium orthoferrite YFeO3 introduced in the course of sample preparation.
__________
Translated from Fizika Tverdogo Tela, Vol. 47, No. 12, 2005, pp. 2182–2188.
Original Russian Text Copyright ? 2005 by Bazuev, Korolev. 相似文献
15.
A. Yu. Kudzin M. D. Volnyanskii M. P. Trubitsyn I. A. Busoul 《Physics of the Solid State》1998,40(12):1994-1997
The dielectric permittivity of Ni-doped Li2Ge7O15 crystals was studied in the vicinity of the ferroelectric phase transition. Introduction of Ni has been shown to suppress
the dielectric anomaly and to reduce substantially the transition temperature. A temperature hysteresis in ɛ (T) has been observed in nominally pure and Ni-doped Li2Ge7O15 crystals near the transition point. Measurements performed under cooling from the paraphase reveal dispersion of dielectric
permittivity at Debye relaxation frequencies of the order of 104–105 Hz at T
c
. It is proposed that the hysteresis phenomena and the low-frequency dispersion are caused by residual defects (of the type
of random local fields), which become polarized in the ferroelectric phase and become disordered above T
c
.
Fiz. Tverd. Tela (St. Petersburg) 40, 2198–2201 (December 1998) 相似文献
16.
N. V. Kazak N. B. Ivanova V. V. Rudenko A. D. Vasil’ev D. A. Velikanov S. G. Ovchinnikov 《Physics of the Solid State》2009,51(5):966-969
Ludwigite single crystals of compositions Co3O2BO3 and Co3 − x
Fe
x
O2BO3 (x ≈ 0.14) have been synthesized. The crystal structure is investigated at room temperature, and the magnetization is studied
in the temperature range T = 4.2–100 K in magnetic fields of up to 600 Oe. The orthorhombic symmetry is revealed, and the unit cell parameters are determined.
A number of features are established for the temperature dependence of the magnetization. In unsubstituted Co3O2BO3, two magnetic transitions are found at T
C1 = 43 K and T
C2 = 15 K. At temperatures below 40 K, spin-glass state is revealed. Substitution of iron ions for cobalt ions leads to a noticeable
shift in the magnetic transitions toward the high-temperature range: T
C1 = 83 K and T
C2 = 74 K. A ferromagnetic ordering of the P type is found in the Co3 − x
Fe
x
O2BO3 (x ≈ 0.14) compound.
Original Russian Text ? N.V. Kazak, N.B. Ivanova, V.V. Rudenko, A.D. Vasil’ev, D.A. Velikanov, S.G. Ovchinnikov, 2009, published
in Fizika Tverdogo Tela, 2009, Vol. 51, No. 5, pp. 916–919. 相似文献
17.
A. N. Vasil’ev 《JETP Letters》1999,69(11):876-880
An antiferromagnetic transition is observed in the quasi-one-dimensional metal-oxide compound LiCuVO4. A wide peak is observed in the temperature dependence of the magnetic susceptibility at T
M
=28 K, and the magnetic susceptibility exhibits a sharp drop at T
N
≈4 K. As the magnetic field increases, the antiferromagnetic-ordering temperature T
N
=2.3 K at first increases somewhat and then decreases rapidly. The exchange interaction in the chains of copper-oxygen octahedra
is estimated to be J
1=22.5 K. The interchain interaction is estimated to be J
2∼1 K.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 828–831 (10 June 1999) 相似文献
18.
A study of the thermal expansion coefficient (TEC) of the ScxTi1−x
Fe2 itinerant magnets has been made within the 5–1200 K range at the transition from the TiFe2 antiferromagnet (T
N=270 K) to the ScFe2 ferromagnet (T
C=540 K). A negative TEC magnetic contribution α
m(T) has been found, which is associated with the formation of spin-fluctuation-induced local magnetic moments in both the magnetically
ordered and the paramagnetic state. The specific features in the α
m(T) dependence are shown to be due to the shape of the density-of-states function near the Fermi level.
Fiz. Tverd. Tela (St. Petersburg) 41, 2174–2178 (December 1999) 相似文献
19.
V. F. Gantmakher G. E. Tsydynzhapov L. P. Kozeeva A. N. Lavrov 《Journal of Experimental and Theoretical Physics》1999,88(1):148-156
A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa2Cu3O6+x
crystals in the range T
c≲30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly
with magnetic field, and in the range T≲13 K it decreased with increasing magnetic field. The transition point T
c(B) was determined by analyzing the fluctuation conductivity. The curves of B
c2(T) measured in the region T/T
c≳0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood
of T
c. The only difference among the curves of B
c2(T) for different crystal states is the scales of Tand B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov’s model of boson superconductivity.
Zh. éksp. Teor. Fiz. 115, 268–284 (January 1999) 相似文献
20.
I. G. Kuleev A. T. Lonchakov I. Yu. Arapova G. I. Kuleev 《Journal of Experimental and Theoretical Physics》1998,87(1):106-114
A new effect of the reduction in the rate of phonon scattering by the spatially correlated system of iron ions in HgSe:Fe
crystals is detected experimentally and calculated theoretically. The thermoelectric power is measured using HgSe:Fe samples
with different iron content in the temperature range 7.5–60 K. It is found that the dependence of the thermoelectric power
on iron content exhibits remarkable features at T<10 K: the quantity |α(N
Fe
)| increases as the iron concentration increases to N
Fe
=5×1018 cm−3, reaches a maximum at N
Fe
≈(1–2)×1019 cm−3, but then monotonically decreases with further increases in N
Fe
. It is shown that the obseved increase in the thermoelectric power is due to a reduction in the rate of phonon scattering
by the spatially correlated system of Fe3+ ions. This new effect is analyzed theoretically, and the theoretical results are compared with the experimental data.
Zh. éksp. Teor. Fiz. 114, 191–207 (July 1998) 相似文献