# Berlin 2012 – wissenschaftliches Programm

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# MA: Fachverband Magnetismus

## MA 27: Half-metals and Oxides (jointly with TT)

### MA 27.8: Vortrag

### Mittwoch, 28. März 2012, 11:30–11:45, EB 202

**Cation distributions and its influence on magnetostrictive properties in inverse spinel ferrites CoFe**_{2}**O**_{4}** and NiFe**_{2}**O**_{4} — •Daniel Fritsch and Claude Ederer — School of Physics, Trinity College Dublin, Ireland

Spinel ferrites CoFe_{2}O_{4} (CFO) and NiFe_{2}O_{4} (NFO) are both insulating ferrimagnetic oxides with a high magnetic ordering temperature and large saturation magnetisation. Moreover, CFO is a highly magnetostrictive material, i.e., it shows a large length change when exposed to a magnetic field.

The spinel structure consists of two magnetic sublattices, namely A- and B-sublattice, which in the *normal* spinel structure are solely occupied by one of the two cation species. An increasing exchange between the two cation species leads to the *inverse* spinel structure where two cation species are distributed over the
B-sublattice. These different possible cation distributions over the B-sublattice strongly influence the total energy of these materials [1].

It has already been shown that density functional theory (DFT) calculations together with the Hubbard “+U” approach provide reliable insight in the structural and magnetic properties of these materials [2]. Here we present DFT total energy calculations for CFO and NFO with different possible cation distributions over the B-sublattice and their influence on the magnetostrictive properties. These results are compared to available experimental data.

[1] D. Fritsch and C. Ederer, Appl. Phys. Lett. **99**, 081916 (2011).

[2] D. Fritsch and C. Ederer, Phys. Rev. B **82**, 104117 (2010).