1,484 research outputs found
On the absence of conduction electrons in the antiferromagnetic part of the phase-separated states in magnetic semiconductors
We have calculated the energies of the phase-separated states for degenerate
antiferromagnetic semiconductors including the possibility of the existence of
conduction electrons in the antiferromagnetic part of the phase-separated
states. It is demonstrated that, at T=0, the minimum energy corresponds to a
droplet phase with absence of electrons in the antiferromagnetic part.Comment: 13 pages, 4 figure
Large nonzero-moment magnetic strings in antiferromagnetic crystals of the manganite type
The magnetic strings in antiferromagnetic crystals with the spin
differ from the magnetic polarons (ferrons) by the absence of the additional
magnetic moment. We show that in the double exchange crystals with
the antiferromagnetic exchange, a new type of magnetic strings appears,
which possesses a magnetic moment. It is concentrated at the center of the
string, and the magnetized string is, in its essence, the state intermediate
between the string and the ferron. In antiferromagnetic manganites, this moment
is by an order of magnitude larger than that of a magnetic atom. Unlike the
conventional ferrons, the magnetization of the strings exists at any parameters
of the crystals under consideration. We argue that this new type of magnetic
state can be relevant to some doped antiferromagnets including manganites.Comment: 7 pages, 1 eps figure, RevTeX, submitted to Phys. Rev.
Edgeworth expansions in operator form
An operator form of asymptotic expansions for Markov chains is established.
Coefficients are given explicitly. Such expansions require a certain
modification of the classical spectral method. They prove to be extremely
useful within the context of large deviations.Comment: 12 page
Phase diagram as a function of temperature and magnetic field for magnetic semiconductors
Using an extension of the Nagaev model of phase separation (E.L. Nagaev, and
A.I. Podel'shchikov, Sov. Phys. JETP, 71 (1990) 1108), we calculate the phase
diagram for degenerate antiferromagnetic semiconductors in the T-H plane for
different current carrier densities. Both, wide-band semiconductors and
'double-exchange' materials, are investigated.Comment: 5 pages, 6 figures, RevTex, Accepted for publication in PR
Stabilization of magnetic polarons in antiferromagnetic semiconductors by extended spin distortions
We study the problem of a magnetic polaron in an antiferromagnetic
semiconductor (ferron). We obtain an analytical solution for the distortion
produced in the magnetic structure of the d-spins due to the presence of a
charge carrier bound to an impurity. The region in which the charge carrier is
trapped is of the order of the lattice constant (small ferron) but the
distortion of the magnetic structure extends over much larger distance. It is
shown that the presence of this distortion makes the ferron more stable, and
introduces a new length scale in the problem.Comment: 5 pages, 1 figure, RevTex 4, submitted to PRB; v2: one reference
added, minor changes in the experiment discussion; v3: minor changes in tex
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