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1

HPM Generation by Tri-Anode Coaxial Vircator

100%

Shao H., Liu G., Zhang Y., Yang Z., Sun J., Zhang Y.

Acta Physica Polonica A

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2009

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vol. 115

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issue 6

1047-1049

EN

A novel type of coaxial vircator with 3 anodes is proposed. The advantages on high power microwave generation is tested by particle-in-cell simulation and theoretical analysis model is set up as well. The tri-anode coaxial vircator behaves a very stable frequency in the pulse duration. In the tri-anode coaxial vircator, the injecting electron beam is well premodulated in the first anode cavity and forms an inerratic bunch-dispersion mechanism in the second anode cavity; the energy-loss electrons penetrate through the third anode and absorbed by the dumping cavity locates in the centre electrode, which helps keeping the bunch-dispersion cycle undisturbed. A 3.8 GHz tri-anode coaxial vircator is theoretically designed and optimized by particle-in-cell simulation, which gives beam-wave conversion efficiency of over 20% with a stable predominant frequency, in accordance with the particle-in-cell simulation and analytic model.

2

A ^{55}Mn NMR Study of La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 with ^{16}O and ^{18}O

63%

Rybicki D., Kapusta C., Riedi P., Oates C., Sikora M., Zając D., De Teresa J., Marquina C., Ibarra M.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

183-188

EN

A ^{55}Mn NMR study of ^{16}O and ^{18}O containing La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 is reported. The spin-echo spectra measured at 4.2 K and zero field consist of a double exchange line corresponding to the ferromagnetic metallic regions. The line intensity is more than an order of magnitude lower for the ^{18}O compound, which indicates an order of magnitude lower content of the ferromagnetic metallic phase in this compound. The frequency dependence of the spin-spin relaxation time T_2 shows a pronounced minimum at the center of the double exchange line of both compounds due to the Suhl-Nakamura interaction, which indicates that the ferromagnetic metallic regions are at least 10~nm in size. The results are discussed in terms of the influence of oxygen isotopic substitution on phase segregation.

3

An NMR study of Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03)

63%

Oates C., Kapusta C., Riedi P., Sikora M., Zając D., Rybicki D., Martin C., Yaicle C., Maignan A.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

189-195

EN

An NMR study of polycrystalline Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03) at 3 K is presented. Zero field spin-echo spectra of the Ga doped compound consist of an overlapping ^{69,71}Ga signal at 74~MHz (hyperfine field of 5.3 T), a ^{55}Mn double exchange line at 375 MHz (35.5 T) and a weak Mn^{3+} signal between 400 and 550 MHz. Measurements in an applied field show a step-like increase in the double exchange line intensity, which corresponds to an increase in the amount of the ferromagnetic metallic phase. This coincides with a step-like feature in the bulk magnetization measurements. The effect is similar to that in the previous field dependent ^{55}Mn NMR measurements of Pr_{0.67}Ca _{0.33}MnO_3. At the demagnetized and remanent state, a variation of spin- spin relaxation time, T_2, across the ^{55}Mn line, due to the Suhl-Nakamura interaction is observed, which suggests that the ferromagnetic metallic double exchange regions, at liquid helium temperatures, are at least 4 nm in size.

4

Barrier and Self-Energy Effects in Manganite Tunneling Characteristics

63%

Svistunov V., Revenko Y., Belogolovskii M., Gerasimenko A., Pashkevich Y., Szymczak H., Przyslupski P., Komissarov I.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

87-92

EN

Tunneling conductance spectra of point-contact junctions formed by a sharp Ag tip and two optimally doped manganites La_{0.67}Sr_{0.33}MnO_3 and Nd_{0.67} Sr_{0.33}MnO_3 are measured and analyzed. It was found that the analytical dependence of the differential conductance on voltage strongly depends on the bias sign and dramatically changes after voltage treatments. The data obtained are explained in terms of the Glasman-Matveev model for tunneling across two localized states settled in the barrier near the manganite bulk. Effective functions of electron-boson interaction extracted from self-energy contributions to the experimental characteristics contain signs of phonon and magnon excitations, higher-energy satellites as a result of possible orbital ordering and a hallmark of localized states in the near-barrier region in the form of strong not-well reproduced peaks.

5

Elastic Properties of Double-Layered Manganite La_{1.2}Sr_{1.8-x}Ba_xMn_2O_7 (x=0.0-0.4)

63%

Reddy Y., Prashanth Kumar V., Ramesh S., Venkanna S., Ramana Reddy M., Kistaiah P., Vishnuvardhan Reddy C.

Acta Physica Polonica A

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2008

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vol. 113

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issue 6

1687-1694

EN

The elastic behavior of the sol-gel prepared double-layered manganite system La_{1.2}Sr_{1.8-x}Ba_xMn_2O_7 (x = 0.0-0.4) was investigated at 300 K, employing ultrasonic pulse transmission technique at 1 MHz. The values of elastic moduli and acoustic Debye temperature (θ_D) were computed from longitudinal and shear velocities. The measured values were corrected to zero porosity using Hasselman and Fulrath's formula. The elastic constants of the samples, estimated using Modi's heterogeneous metal-mixture rule, were also reported. The variation of elastic moduli with Ba concentration was interpreted in terms of strength of interatomic bonding.

6

Phase Separation and Microwave Response of Epitaxial and Polycrystalline Manganite Films

51%

Ašmontas S., Abrutis A., Gradauskas J., Lučun A., Oginskis A., Plaušinaitienė V., Sužiedėlis A., Vengalis B.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

141-147

EN

The resistance, magnetoresistance, and resistance response under microwave irradiation (f=10 and 35 GHz) were measured for epitaxial and polycrystalline La_{0.67}Ca_{0.33}MnO_3 and La_{0.67}Sr_{0.33}MnO_3 thin films in the temperature range 78÷300 K. The microwave induced resistance increase observed for the epitaxial films in a narrow temperature range below the ferromagnetic to paramagnetic transition temperature T_c certifies coexistence of low resistance (ferromagnetic) and high resistance (paramagnetic) regions in the manganites. Resistance of polycrystalline films decreased under microwave irradiation in a wide temperature range below T_c. The effect was explained in terms of microwave assisted hopping of carriers in high resistance regions formed at grain boundaries of the polycrystalline films.

7

Raman Study in Pr_{0.5}Ca_{0.5}MnO_3 Thin Films

51%

Tatsi A., Papadopoulou E., Lampakis D., Liarokapis E., Prellier W., Mercey B.

Acta Physica Polonica A

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2004

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vol. 105

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issue 1-2

99-106

EN

We report novel Raman measurements made on Pr_{0.5}Ca_{0.5}MnO_3 thin films grown on SrTiO_3 and LaAlO_3 (PCMO/STO and PCMO/LAO, respectively). The measurements were performed for a temperature range 78 K

8

Development of Carbon Nanotube Based Reflection Type X-ray Source

51%

Choi H., Kim J., Lee C.

Acta Physica Polonica A

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2009

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vol. 115

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issue 6

1078-1080

EN

X-ray imaging technology is a useful and leading medical diagnostic tool for health care professionals to diagnose disease in human body. Carbon nanotube based X-ray source, which we have developed in this study, could be also useful and supply integrated diagnostic X-ray imaging tool in diagnosis. Conventionally, thermionic type of tungsten filament X-ray tube is widely employed in the field of biomedical and industrial application fields. However, intrinsic problems, such as poor emission efficiency, low imaging resolution, and high electrical energy consumption etc., may cause the limitation of using the X-ray tube. To fulfill the current market requirement, specifically for medical diagnostic field, we have developed rather a portable and compact carbon nanotube based X-ray device in which microfocus high imaging resolution can be feasible.

9

Growth and Investigation of Oxide Heterostructures Based on Half-Metallic Fe3O4

51%

Vengalis B., Šliužienė K., Lisauskas V.

Acta Physica Polonica A

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2004

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vol. 105

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issue 6

659-665

EN

We report thin films of ferromagnetic Fe_3O_4 (magnetite) grown by a reactive magnetron sputtering at T=300÷450°C on lattice-matched MgO, and bilayer structures composed of Fe_3O_4 and underlying epitaxial films of highly conductive electron-doped In_2O_3〈Sn〉, LaNiO_3, and antiferromagnetic CoO. The prepared Fe3O4/MgO films and the bilayer structures demonstrated clearly defined resistance anomaly at Verwey transition point (T_V≈100-120 K). Formation of high resistance interlayer was indicated between the adjacent conducting Fe3O4 and LaNiO3 layers. However, relatively low interface resistivity of about 0.1 Ω cm^2 (at T=300 K) was estimated for the patterned Fe3O4/In2O3〈Sn〉 bilayer structures. Vertical electrical transport measurements revealed strong nonlinearity in the I-U dependences of the Fe3O4/In2O3 〈Sn〉 interface at T

10

Fast Electrical Switching of Thin Manganite Films

51%

Balevičius S., Kiprijanovič O., Stankevič V., Žurauskienė N., Česnys A., Tolvaišienė S., Abrutis A., Plaušinaitienė V.

Acta Physica Polonica A

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2008

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vol. 113

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issue 3

821-824

EN

51%

Glushkov V., Anisimov M., Batko I., Batkova M., Bogach A., Demishev S., Filipov V., Flachbart K., Kuznetsov A., Sannikov I., Shitsevalova N., Sluchanko N.

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issue 5

891-892

EN

Transport, magnetic and thermal properties of substitutional solid solution Eu_{1 - x}Ca_{x}B_6 single crystals (0 ≤ x ≤ 0.244) have been studied at 1.8 ≤ T ≤ 300 K and in magnetic fields up to 8 T. Calcium doping is shown to result in a metal-insulator transition, which occurs at x_{MIT} ≈ 0.2. In vicinity of metal-insulator transition the effect of colossal magnetoresistance is found to be very sensitive to Ca content, the amplitude varying from Δ = [ ρ (0)- ρ (8T)]/ρ(8T) ≈1.4×10^2 to Δ ≈ 7.5 × 10^3 for 0.14 ≤ x ≤ 0.16. The analysis of magnetic contribution to heat capacity shows that a large amount of magnetic entropy ( ≈ 30%) releases in Eu_{0.845}Ca_{0.155}B_6 when moving from the Curie temperature T_{C} ≈ 5.5 K to the characteristic one T* ≈ 30 K. This observation as well as the large amplitude of low field colossal magnetoresistance effect and the deviation of magnetic susceptibility from the Curie-Weiss law detected for x = 0.155 compound in the interval T_{C} ≤ T ≤ T* seem to be associated with magnetic phase separation induced by Ca doping.

19

Anomalous Transport Properties of Carbon-Doped EuB_6

51%

Batkova M., Batko I., Filipov V., Flachbart K., Sechovský V., Shitsevalova N., Šantavá E., Šebek J.

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issue 5

893-894

EN

In the presented work we report electrical, magnetic and thermal properties of EuB_{6-x}C_{x} single crystals with an estimated value of x ≈ 0.07. Our studies reveal an antiferromagnetic phase transition at T_{N} ≈ 6.7 K. Electrical resistivity at zero magnetic field shows a pronounced resistivity maximum at T_{M} ≈ 7 K, just above the antiferromagnetic phase transition temperature. With increasing applied magnetic field the maximum moves to lower temperature and becomes totally suppressed at the field of 9 T. Observed magnetoresistance is negative in the whole studied temperature range 2-20 K, yielding a ratio of ρ(0 T, 7 K)/ρ(9 T, 7 K) ≈ 2.5. The origin of such magnetoresistance is associated with formation of mixed magnetic structure in the system due to fluctuation of carbon concentration.

20

Magnetoresistance of Polycrystalline La_{0.7}Ca_{0.3}MnO_3 Films in a Microwave Magnetic Field

51%

Lučun A., Butkutė R., Maneikis A., Kiprijanovič O., Anisimovas F., Gradauskas J., Sužiedėlis A., Vengalis B., Kancleris Ž., Ašmontas S.

Acta Physica Polonica A

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2007

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vol. 111

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issue 1

147-152

EN

We present new experimental evidence indicating the importance of magnetic field component of microwave field (f=9.4 GHz) for magnetoresistive properties of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films. The microwave measurements revealed a different character of the temperature-dependent electrical resistance of polycrystalline La_{0.7}Ca_{0.3}MnO_3 films placed in the centre (maximal amplitude of H_{10} wave vector) and at a narrow wall of the wave-guide (reduced H_{10} amplitude). Theoretical estimations of the influence of substrate onto distribution of microwave electric and magnetic fields in the waveguide were performed using the finite-difference time-domain method.

Refine search results

HPM Generation by Tri-Anode Coaxial Vircator

A ^{55}Mn NMR Study of La_{0.33}Nd_{0.33}Ca_{0.34}Mn O_3 with ^{16}O and ^{18}O

An NMR study of Pr_{0.5}Ca_{0.5}Mn_{1-x}Ga_xO_3 (x=0 and 0.03)

Barrier and Self-Energy Effects in Manganite Tunneling Characteristics

Elastic Properties of Double-Layered Manganite La_{1.2}Sr_{1.8-x}Ba_xMn_2O_7 (x=0.0-0.4)

Phase Separation and Microwave Response of Epitaxial and Polycrystalline Manganite Films

Raman Study in Pr_{0.5}Ca_{0.5}MnO_3 Thin Films

Development of Carbon Nanotube Based Reflection Type X-ray Source

Growth and Investigation of Oxide Heterostructures Based on Half-Metallic Fe3O4

Fast Electrical Switching of Thin Manganite Films

Reentrant Metal-Insulator Transition in Ca_{1-x}Eu_{x}B_{6}

Electric Field Distributions in the Open Cylindrical Silicon Carbide Waveguides

Investigation of Magnetoresistance and Its Anisotropy of Thin Polycrystalline La_{0.83}Sr_{0.17}MnO_3 Films in High Pulsed Magnetic Fields

Influence of Pressure on Magnetic Properties of La_{1-x} Sr_xCoO_{3-δ}(x=0.5, 0.67, 1)

Influence of Sr Content on CMR Effect in Polycrystalline La_{1-x}Sr_{x}MnO_{3} Thin Films

Thin Film Manganite-Metal Interconnection and "Loop Effect" Studies in CMR-Based High Magnetic Field Sensors

Numerical Magneto-Mechanical Analysis of Destructive Coils with Reinforcement Cylinders of Various Thicknesses

Charge Transport and Magnetism in Eu_{1-x}Ca_{x}B_6

Anomalous Transport Properties of Carbon-Doped EuB_6

Magnetoresistance of Polycrystalline La_{0.7}Ca_{0.3}MnO_3 Films in a Microwave Magnetic Field