171 research outputs found
Modification of the ground state in Sm-Sr manganites by oxygen isotope substitution
The effect of O O isotope substitution on electrical
resistivity and magnetic susceptibility of SmSrMnO manganites
is analyzed. It is shown that the oxygen isotope substitution drastically
affects the phase diagram at the crossover region between the ferromagnetic
metal state and that of antiferromagnetic insulator (0.4 0.6), and
induces the metal-insulator transition at for = 0.475 and 0.5. The nature
of antiferromagnetic insulator phase is discussed.Comment: 4 pages, 3 eps figures, RevTeX, submitted to Phys. Rev. Let
Nanoscale phase separation in manganites
We study the possibility of nanoscale phase separation in manganites in the
framework of the double exchange model. The homogeneous canted state of this
model is proved to be unstable toward the formation of small ferromagnetic
droplets inside an antiferromagnetic insulating matrix. For the ferromagnetic
polaronic state we analyze the quantum effects related to the tails of
electronic wave function and a possibility of electron hopping in the
antiferromagnetic background. We find that these effects lead to the formation
of the threshold for the polaronic state.Comment: 10 pages, 2 figures, invited talk on the workshop on Strongly
Correlated Electrons in New Materials (SCENM02), Loughborough (UK). submitted
to Journal of Physics A: Mathematical and Genera
Theory of Insulator Metal Transition and Colossal Magnetoresistance in Doped Manganites
The persistent proximity of insulating and metallic phases, a puzzling
characterestic of manganites, is argued to arise from the self organization of
the twofold degenerate e_g orbitals of Mn into localized Jahn-Teller(JT)
polaronic levels and broad band states due to the large electron - JT phonon
coupling present in them. We describe a new two band model with strong
correlations and a dynamical mean-field theory calculation of equilibrium and
transport properties. These explain the insulator metal transition and colossal
magnetoresistance quantitatively, as well as other consequences of two state
coexistence
Phase diagram and isotope effect in (PrEu)_0.7Ca_0.3CoO_3 cobaltites exhibiting spin-state transitions
We present the study of magnetization, thermal expansion, specific heat,
resistivity, and a.c. susceptibility of
(PrEu)CaCoO cobaltites. The measurements were
performed on ceramic samples with and . Based on these
results, we construct the phase diagram, including magnetic and spin-state
transitions. The transition from the low- to intermediate-spin state is
observed for the samples with , whereas for a lower Eu-doping level,
there are no spin-state transitions, but a crossover between the ferromagnetic
and paramagnetic states occurs. The effect of oxygen isotope substitution along
with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope
substitution (O by O) is found to shift both the magnetic and
spin-state phase boundaries to lower Eu concentrations. The isotope effect on
the spin-state transition temperature () is rather strong, but it is
much weaker for the transition to a ferromagnetic state (). The
ferromagnetic ordering in the low-Eu doped samples is shown to be promoted by
the Co ions, which favor the formation of the intermediate-spin state of
neighboring Co ions.Comment: 13 pages, including 11 figures, to be published in Phys. Rev.
Modern forms of community-based psychiatric care in the system of continuing medical education
Changing ideology in the work of the psychiatric service with an emphasis on out-of-hospital forms of work, using a wide range of methods of social integration and restoration of lost functions and skills in patients with mental disorders dictates the need to study and introduce modern forms of out-of-hospital psychiatric care. Such transformations require a change of paternalistic approaches to partnerships with patients, with active involvement and their relatives in the healing process, as well as an increase in the mental health care system of the role of district psychiatrist.ΠΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ ΠΈΠ΄Π΅ΠΎΠ»ΠΎΠ³ΠΈΠΈ Π² ΡΠ°Π±ΠΎΡΠ΅ ΠΏΡΠΈΡ
ΠΈΠ°ΡΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠ»ΡΠΆΠ±Ρ Ρ Π°ΠΊΡΠ΅Π½ΡΠΎΠΌ Π½Π° Π²Π½Π΅Π±ΠΎΠ»ΡΠ½ΠΈΡΠ½ΡΠ΅ ΡΠΎΡΠΌΡ ΡΠ°Π±ΠΎΡΡ Ρ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΠ΅ΠΌ ΡΠΈΡΠΎΠΊΠΎΠ³ΠΎ ΡΠΏΠ΅ΠΊΡΡΠ° ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊ ΡΠΎΡΠΈΠ°Π»ΡΠ½ΠΎΠΉ ΠΈΠ½ΡΠ΅Π³ΡΠ°ΡΠΈΠΈ ΠΈ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ ΡΡΡΠ°ΡΠ΅Π½Π½ΡΡ
ΡΡΠ½ΠΊΡΠΈΠΉ ΠΈ Π½Π°Π²ΡΠΊΠΎΠ² Ρ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠΎΠ² Ρ ΠΏΡΠΈΡ
ΠΈΡΠ΅ΡΠΊΠΈΠΌΠΈ ΡΠ°ΡΡΡΡΠΎΠΉΡΡΠ²Π°ΠΌΠΈ Π΄ΠΈΠΊΡΡΠ΅Ρ Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠΎΡΡΡ ΠΈΠ·ΡΡΠ΅Π½ΠΈΡ ΠΈ Π²Π½Π΅Π΄ΡΠ΅Π½ΠΈΡ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΡ
ΡΠΎΡΠΌ Π²Π½Π΅Π±ΠΎΠ»ΡΠ½ΠΈΡΠ½ΠΎΠΉ ΠΏΡΠΈΡ
ΠΈΠ°ΡΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠΌΠΎΡΠΈ. Π’Π°ΠΊΠΈΠ΅ ΠΏΡΠ΅ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΡ ΡΡΠ΅Π±ΡΡΡ ΡΠΌΠ΅Π½Ρ ΠΏΠ°ΡΠ΅ΡΠ½Π°Π»ΠΈΡΡΡΠΊΠΈΡ
ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ΠΎΠ² Π½Π° ΠΏΠ°ΡΡΠ½Π΅ΡΡΠΊΠΈΠ΅ ΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡ Ρ ΠΏΠ°ΡΠΈΠ΅Π½ΡΠ°ΠΌΠΈ Ρ Π°ΠΊΡΠΈΠ²Π½ΡΠΌ ΠΏΡΠΈΠ²Π»Π΅ΡΠ΅Π½ΠΈΠ΅ΠΌ ΠΈ ΠΈΡ
ΡΠΎΠ΄ΡΡΠ²Π΅Π½Π½ΠΈΠΊΠΎΠ² ΠΊ Π»Π΅ΡΠ΅Π±Π½ΠΎΠΌΡ ΠΏΡΠΎΡΠ΅ΡΡΡ, Π° ΡΠ°ΠΊΠΆΠ΅ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΠ΅ Π² ΡΠΈΡΡΠ΅ΠΌΠ΅ ΠΎΠΊΠ°Π·Π°Π½ΠΈΡ ΠΏΡΠΈΡ
ΠΈΠ°ΡΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΏΠΎΠΌΠΎΡΠΈ ΡΠΎΠ»ΠΈ ΡΡΠ°ΡΡΠΊΠΎΠ²ΠΎΠ³ΠΎ Π²ΡΠ°ΡΠ°-ΠΏΡΠΈΡ
ΠΈΠ°ΡΡ
Percolative conductivity and critical exponents in mixed-valent manganites
Recent experiments have shown that some colossal magnetoresistance (CMR)
materials exhibit a percolation transition. The conductivity exponent varies
substantially with or without an external magnetic field. This finding prompted
us to carry out theoretical studies of percolation transition in CMR systems.
We find that the percolation transition coincides with the magnetic transition
and this causes a large effect of a magnetic field on the percolation
transition. Using real-space-renormalization method and numerical calculations
for two-dimensional (2D) and three-dimensional (3D) models, we obtain the
conductivity exponent to be 5.3 (3D) and 3.3 (2D) without a magnetic field,
and 1.7 (3D) and 1.4 (2D) with a magnetic field.Comment: 4 pages, 4 figures. To appear in Rapid Communications of Phys. Rev.
Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei
The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the "brute force" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the Sb, Sb and
I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio
Isotope effects and the charge gap formation in the charge ordered phase of colossal magnetoresistance manganites
Giant oxygen isotope effects observed in colossal magnetoresistance
manganites are investigated by employing the combined model of the double
exchange and interacting lattice polaron mechanism. We have shown that the
isotope effects on in the metallic phase and in the charge
ordered phase of manganites can be explained well in terms of the double
exchange and polaron narrowing factors with reasonable physical parameters.Comment: 5 pages, 3 figure
Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)
All the three series of manganates showsaturation magnetization
characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with
increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2
respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably
smaller showing a small increase around TM, the value of TM decreasing slightly
with increase in x or decrease in . The ferromagnetic compositions (x xc)
show insulator-metal (IM) transitions, while the compositions with x > xc are
insulating. The magnetic and electrical resistivity behavior of these
manganates is consistent with the occurrence of phase separation in the
compositions around xc, corresponding to a critical average radius of the
A-site cation, , of 1.18 A. Both Tc and TIM increase linearly when < rA
> > or x xc as expected of a homogenous ferromagnetic phase. Both Tc
and TM decrease linearly with the A-site cation size disorder at the A-site as
measured by the variance s2. Thus, an increase in s2 favors the insulating AFM
state. Percolative conduction is observed in the compositions with > <
rAc >. Electron transport properties in the insulating regime for x > xc
conforms to the variable range hopping mechanism. More interestingly, when x >
xc, the real part of dielectric constant (e') reaches a high value (104-106) at
ordinary temperatures dropping to a very small (~500) value below a certain
temperature, the value of which decreases with decreasing frequency.Comment: 27 pages; 11 figures, Submitted to J.Phys:Condens Matte
Dysfunction of vascular endothelium at arterial hypertension and coronary disease (literature review)
This review presents the observation of the role of endothelial dysfunction in development of atherosclerosis, coronary disease and. hypertension. Among other causes of endothelial dysfunction the most significant are hemodynamic factors (wall transverse strain, transmural pressure), dyslipoproteinemia, hyperhomocysteinemia, hyperglycemia, free radical damage of endothelium. It is supposed that in development and. progressing of coronary disease more significant role may belong to endothelial dysfunction rather than to morphological vascular changes, predetermined by atherosclerosis. However, there is still no clear view of development of endothelial dysfunction and. mechanisms of development and. progressing of both isolated forms of coronary disease and arterial hypertension and their combination
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