Exchange Interactions in CrO$_2$ studied with density functional theory
msra(2009)
摘要
We report a study of exchange interactions in bulk CrO$_2$ calculated from
first principles. We considered three near neighbor Cr-Cr exchange
interactions: the interaction between corner and body center atoms mediated
through a single oxygen atom; the interaction between a Cr and the Cr directly
"above" it in the (001) direction, also mediated by a single O atom; and the
interaction between a Cr and its neighbor in the (100) direction, mediated by
two intervening oxygen atoms. The interactions were calculated by rotating the
moments of one or more of the Cr ions while constraining the others to remain
parallel. We then fit the resulting energy vs. angle data to the Heisenberg
model and extracted exchange energy parameters with a least-squares method. We
also calculated the exchange interactions using a "spin-spiral" technique, in
which a relative angular displacement was imposed upon Cr moments in adjacent
cells. Similar results were obtained with both approaches. The calculated T=0 K
exchange interactions were subsequently used to determine the magnetization as
a function of temperature via low-T spin-wave dispersion and a Monte-Carlo
method. Reasonable agreement with experiment was obtained.
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关键词
materials science,density function theory,first principle,spin wave,monte carlo method,heisenberg model,exchange interaction,least square method
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