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Influence of Acoustic Phonons on the Magnetic Anisotropy in GaMnAs Magnetic Semiconductors

100%
Jasiukiewicz C., Stagraczyński S., Lehmann D., Dugaev V., Berakdar J.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2
179-181
EN
We present a theoretical description of the influence of incoherent acoustic phonons on the magnetic anisotropy of magnetic semiconductors. Our theory is based on the six-band Kane model of the electron energy spectrum describing the valence band with k· p Hamiltonian including the hole-phonon interaction term. We include the effect of incoherent phonons through the hole self-energy in the six-band model, and assume a strong laser-pulse-induced flux of non-equilibrium acoustic phonons. The results of numerical calculations of magnetic anisotropy performed for (GaMn)(AsP) magnetic alloy semiconductors demonstrate the essential role of incoherent phonons.
2
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I-V Characteristics of Resistive Oxides: DC versus Pulsed Measurements

100%
Fisher B., Genossar J., Chashka K., Patlagan L., Reisner G.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
57-61
EN
We investigated pulsed and DC I-V characteristics of a variety of resistive oxides. Examples of pulsed, compared with DC characteristics, are shown for samples of La_{1.2}Sr_{1.8}Mn_2O_7 (a double layer manganite), Pr_{2/3}Ca_{1/3}MnO_3 and Bi_{1/2}Sr_{1/2}MnO_3 (charge-ordered manganites), Sr_2FeMoO_6, Sr_2CrWO_6 and Ba_2MnReO_6 (double perovskites). For pulsed measurements, single pulses in the ms range were applied. For short-rise-time square pulses, the Joule heating is negligible, as long as the response remains independent of time. The DC I-V characteristics were measured up to current runaway in the negative resistance regime;Δ T never exceeded a fraction of a degree. In most cases the DC characteristics mask a perfectly ohmic or moderately non-ohmic conductivity obtained by pulsed measurements. This demonstrates that the widely used DC I-V measurements in the high current regime are frequently misleading.
3
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Ferroelectric Field Effect Transistor Based on Modulation Doped CdTe/CdMgTe Quantum Wells

100%
Kolkovsky V., Wojciechowski T., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1173-1178
EN
In this work, we observed effects of changing the electron concentration and electron mobility upon the poling of the Cd_{0.96}Zn_{0.04}Te ferroelectric gate deposited on the top of the CdTe-based modulation doped quantum well structure, which are confirmation of the existence of the electrostatic field originating from the ferroelectric material, which can be controlled by an external voltage. The analysis of the data obtained from the Hall effect measurements showed that the electron mobility and carrier concentration decreased by a factor of 2.5 and 1.5, respectively upon the negative poling of the gate with respect to the poled by the positive voltage. Moreover, the electrostatic field, depending on its directions, causes depletion of accumulation of electrons in the 2D channel, i.e., it is a source of the field effect.
4
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Study of Candidate Insulating Materials for Use in Shock Wave Switches

75%
Kolosenok S., Altgilbers L.
Acta Physica Polonica A
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2009
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vol. 115
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issue 6
1010-1012
EN
One challenge in high power switching is to have a compact switch, which can hold off high voltages and close rapidly at the proper time. Most high power switches are large or complicated, such as triggered spark gaps. Typical opening switches are also not compact and often have too long switching time. It has been shown previously that certain insulating materials undergo a drastic change in conductivity under shock loading. Using such a material could greatly reduce the size of a switch. We will report on our continuing studies of different candidate materials for shock wave switches.
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