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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2005. V. 8, N 3. P. 030-038.
Polaron effects in exchange clusters (V2+−F-−V2+ in KMgF3)
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine,
45, prospect Nauky, 03028 Kyiv, Ukraine,
E-mail: kashirin@class.semicond.kiev.ua
Abstract. We have calculated the phonon contribution to the energy of a superexchange.
It is shown that the phonon contribution to the exchange interaction is comparable on the
order of magnitude with the Coulomb superexchange. The numerical calculations are
performed for a molecular cluster consisting of an exchange-coupled pair V 2+−F–
−V 2+
and 10 nearest ions F-
in KMgF3. The distinctions of a temperature dependence of the
exchange interaction caused by phonons are discussed. In systems with the close located
electronic levels, the account of interaction with a phonon field reduces in occurrence of
resonant terms in the exchange interaction of paramagnetic ions. The similar terms result
in occurrence of the exponential temperature dependence in an exchange interaction. As
an example, the exchange pair of 2+ Cu ions in K2CuCl 4 ⋅ 2H2O has been considered.
The experimentally observed anomalously strong temperature dependence of the
exchange interaction of copper ions in this system can be described by the contribution of
the resonant terms caused by a phonon contribution to the exchange interaction. The total
exchange can be described by the dependence 1
Σ 0 1( 1)
− ≈ − −x I I I e , where ΣI is the
complete exchange interaction in a system including the phonon contribution (the second
term) , x = δ / k0T with the parameters I0 ≅ 0.29 Κ , I1 ≅ 0.22 Κ , δ ≅ 192 Κ . The
parameter δ corresponds to the splitting of a doubly degenerated lowest term of the
copper ion in the crystalline field.
Keywords: an orbital-lattice interaction, exchange-coupled pairs, indirect spin-spin
interactions.
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