44 research outputs found
Перспективи консоціальної демократії
Аналізується сучасний політичний режим України; висвітлюються проблеми та
недоліки політичної системи, обґрунтовуються альтернативні шляхи їх подолання.
Розглянуто ідею республіканської держави та можливість її запровадження в Україні
шляхом застосування окремих елементів моделі консоціональної демократії А. Лейпхарта.
This article analyses the current political regime in Ukraine; shows the problems and drawbacks of the political system; grounds the alternative ways to overcome them. It also
investigates the idea of Republican state and the possibility of its implementation in Ukraine through the usage of some elements of Lijphart’s consociation democracy
Vortex-like state observed in ferromagnetic contacts
Point-contacts (PC) offer a simple way to create high current densities, 10^9
A/cm^2 and beyond, without substantial Joule heating. We have shown recently
(Nano Letters, 7 (2007) 927) that conductivity of nanosized PCs between a
normal and ferromagnetic metals exhibits bi-stable hysteretic states versus
both bias current and external magnetic field - the effect typical for
spin-valve structures. Here we report that apart from the bi-stable state a
third intermediate-resistance state is occasionally observed. We interpret this
state as due to a spin-vortex in the PC, nucleated either by Oersted field of
the bias current and/or by the circular geometry of PC. The observed
three-level-states in the PC conductivity testify that the interface spins are
both weakly coupled to the spins in the bulk and have depressed exchange
interaction within the surface layer.Comment: 4 pgs., 4 figs. submitted to ICM-09 (July 26-21, Karlsruhe) V2:
corrected typos, accepted for publication in J. Phys.: Conf. Serie
Spin Torques in Point Contacts to Exchange-Biased Ferromagnetic Films
Hysteretic magneto-resistance of point contacts formed between non-magnetic
tips and single ferromagnetic films exchange-pinned by antiferromagnetic films
is investigated. The analysis of the measured current driven and field driven
hysteresis agrees with the recently proposed model of the surface spin-valve,
where the spin orientation at the interface can be different from that in the
bulk of the film. The switching in magneto-resistance at low fields is observed
to depend significantly on the direction of the exchange pinning, which allows
identifying this transition as a reversal of interior spins of the pinned
ferromagnetic films. The switching at higher fields is thus due to a spin
reversal in the point contact core, at the top surface of the ferromagnet, and
does not exhibit any clear field offset when the exchange-pinning direction or
the magnetic field direction is varied. This magnitude of the switching field
of the surface spins varies substantially from contact to contact and sometimes
from sweep to sweep, which suggests that the surface coercivity can change
under very high current densities and/or due to the particular microstructure
of the point contact. In contrast, no changes in the effect of the exchange
biasing on the interior spins are observed at high currents, possibly due to
the rapid drop in the current density away from nanometer sized point contact
cores.Comment: 3 pages, 3 figs, presented on 11th Joint MMM-Intermag Conference,
Jan. 18-22, 2010, Washington, US
Spectroscopy of phonons and spin torques in magnetic point contacts
Phonon spectroscopy is used to investigate the mechanism of current-induced
spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization
excitations observed in the magneto-conductance of the point contacts are
pronounced for diffusive and thermal contacts, where the electrons experience
significant scattering in the contact region. We find no magnetic excitations
in highly ballistic contacts. Our results show that impurity scattering at the
N/F interface is the origin of the new single-interface spin torque effect.Comment: 4 pages, 5 figs., accepted for publication in PR
Stimulated emission and absorption of photons in magnetic point contacts
Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal
Cu are used to achieve a strong spin-population inversion in the contact core.
Subjected to microwave irradiation in resonance with the Zeeman splitting in
Cu, the inverted spin-population relaxes through stimulated spin-flip photon
emission, detected as peaks in the point contact resistance. Resonant spin-flip
photon absorption is detected as resistance minima, corresponding to sourcing
the photon field energy into the electrical circuit. These results demonstrate
fundamental mechanisms that are potentially useful for designing metallic
spin-based lasers.Comment: 11 pages, 5 fig
Phonon structure in I-V characteristic of MgB point-contacts
The search of the phonon structure at the above-gap energies was carried out
for spectra of MgB point contacts with a normal metal.
The two-band model is assumed not only for the gap structure in
-characteristics, but also for phonons in
point-contact spectra, with up to the maximum lattice vibration energy. Since
the current is carried mostly by charges of 3D-band, whereas the strong
electron-phonon interaction occurs in 2D-band, we observe the phonon
peculiarities due to ''proximity'' effect in {\it k}-space, which depends on
the variation of interband coupling through the elastic scattering.Comment: 6 pages, 4 figures, revtex4, reported in International Conference
"Modern Problems in Superconductivity", 9-13 September, Yalta, Ukrain