4,794 research outputs found
Re-entrant ferromagnetism in a generic class of diluted magnetic semiconductors
Considering a general situation where a semiconductor is doped by magnetic
impurities leading to a carrier-induced ferromagnetic exchange coupling between
the impurity moments, we show theoretically the possible generic existence of
three ferromagnetic transition temperatures, T_1 > T_2 > T_3, with two distinct
ferromagnetic regimes existing for T_1 > T > T_2 and T < T_3. Such an
intriguing re-entrant ferromagnetism, with a paramagnetic phase (T_2 > T > T_3)
between two ferromagnetic phases, arises from a subtle competition between
indirect exchange induced by thermally activated carriers in an otherwise empty
conduction band versus the exchange coupling existing in the impurity band due
to the bound carriers themselves. We comment on the possibility of observing
such a re-entrance phenomenon in diluted magnetic semiconductors and magnetic
oxides.Comment: 4 pages, 3 figure
A disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors
We develop a lattice mean field theory for ferromagnetic ordering in diluted
magnetic semiconductors by taking into account the spatial fluctuations
associated with random disorder in the magnetic impurity locations and the
finite mean free path associated with low carrier mobilities. Assuming a
carrier-mediated indirect RKKY exchange interaction among the magnetic
impurities, we find substantial deviation from the extensively used continuum
Zener model Weiss mean-field predictions. Our theory allows accurate analytic
predictions for Tc, and provides simple explanations for a number of observed
anomalies including the non-Brillouin function magnetization curves, the
suppressed low-temperature magnetization saturation, and the dependence of Tc
on conductivity.Comment: 5 pages, 2 figure
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