Interactions superexchange

In further studies along this line. Greenwood et al. have examined the magnetic superexchange interactions in the solid solution series La cCai cRu03 (0 < x... 

Moriya, T. 1960. Anisotropic superexchange interaction and weak ferromagnetism. Physical Review 120 91-98. 

The general framework of the quantum mechanical rate expression for long-range electron transfer processes in the very weak or non-adiabatic regime will be presented in Sect. 2 with an emphasis on the inclusion of superexchange interactions. The relation between the simplest case of direct donor-acceptor interactions, on the one hand, and long-range electronic interactions important in proteins, on the other, is considered in terms of the elements of electron transfer theory. 

At long range the direct interaction with the final state (D A ), similarly a zeroth order state, may be negligibly small relative to the contribution from superexchange interactions at that distance. The (unknown) solution for the Hamiltonian including interactions (H = H -I- V), is... 

Tab. 6.3 Exchange constants for superexchange interactions in hematite (Samuelson Shirane, 1970 with permission)...

In the spinel structure three coordination octahedra meet in one corner, the corresponding Cr—O—Cr bond-angles being about 95°, however, which is unfavourable for electron-delocalisation efiects, i. e. superexchange interactions. 

This finding is not surprising it has been anticipated in the small magnitudes of the FeA-O-O-FeA superexchange interactions. It follows from the following two considerations ... 

EuO is an interesting oxide in the rocksalt family (Honig Van Zandt, 1975). It is a ferromagnetic T = 69 K) insulator when pure and stoichiometric. Unlike the M oxides, superexchange interaction in EuO is ferromagnetic because the charge transfer... 

In doped semiconductors I is due to direct overlap in transitional-metal oxides the overlap between the d-orbitals is frequentiy via the oxygen ions and is then often called a superexchange interaction. Figure 3.4 shows the kinds of wave function expected. As regards magnitudes, if B 1 eV, 17 10 eV and z=4, kBTN should be 0.01 eV so that 100K, which shows why low Neel temperatures are common. 

Interestingly, metal-metal interaction appears to be dependent on the oxidation state of the system. This is clearly evidenced by the results obtained for Os2 in liquid SO2 at —70°C, in that in these experimental conditions both the first and the second oxidation of each metal center can be seen (Fig. 5.4 Table 5.1).15 Potential splitting for the first oxidation process is 370 mV, whereas potential splitting for the second oxidation process is 150 mV. This result confirms the electron transfer pathway for the superexchange interaction once mono-oxidized, the Os(III)-based orbitals are stabilized and their interaction with the bridge-based LUMO orbitals decreases. A similar result has been recently obtained in molecular grids based on similar polypyridine ligands.25... 

Let us consider a fixed value of parameter. Hence, the values of local orbital angles are well defined. In this case the superexchange interaction for the pair of JT ions can be written as follows [12] ... 

First-order Phase Transition in U02 The Interplay of the 5f2-5f2 Superexchange Interaction and Jahn-Teller Effect... 

The aim of this work is to elucidate these problems. To this end, we calculate the effective spin Hamiltonian of the 5f2—5f2 superexchange interaction between the neighboring U4+ ions in the cubic crystal lattice of UO2 and we calculate T5 <%> eg, rs f2g(l) ancl r5 f2g(2) linear vibronic coupling constants. These data are then used to draw a more definite conclusion about the driving force of the phase transition and especially about the actual mechanism of the spin and orbital ordering in U02. 

---