P4

Double perovskites with high spin polarization (Tremel)

Half-metallic ferrimagnetic double perovskites of the A2MM’O₆ type are highly promising candidates for powder magnetoresistance based spintronic devices. Despite the comparably low efforts required in synthesizing polycrystalline samples, the elucidation of their optimum magnetoresistance behaviour and their suitability for industrial applications is highly biased by grain boundaries and defects. In order to understand the underlying physical effects in these compounds, in detail and to optimize their magnetoresistance behaviour, the electronic structure, magnetic properties and the element specific magnetic moments have to be studied – all achievable within the network of participating groups (P 5, P 7, P 9) – on unbiased materials, i.e. single crystals. All of these studies can be performed within the network of the participating groups (P 5, P 7, P 9). Accordingly, one a focus for the next funding period will be focus on (i) single crystal growth of pure and selected doped phases, and (ii) the study of cation-cation disorder- and phase separation phenomena. (iii) In order to shed light on the exchange mechanisms in molybdate/tungstate and rhenate double perovskites, (iii) the synthesis of the still unknown and non computable technetate Sr₂FeTcO₆ will be pursued. (iv) To optimize the position of the Fermi level with respect to the van Hove -singularity, (iv) the solid solution series Sr₂FeRe_1-xM’_xO₆(M’ = Mo, W) will be studied. Suitable candidates from this series will be chosen for studies on single crystal growth.