DYNAMIC SHORT-RANGE ORDER OBSERVED IN THE (ZN)[FE-2]O-4 SPINEL BY NEUTRON-DIFFRACTION, MU-SR, AND MOSSBAUER EXPERIMENTS

Using neutron diffraction (ND), muon-spin rotation/relaxation (mu SR), and Fe-57-Mossbauer spectroscopy (MS) we have investigated magnetic p roperties of the normal spinel (Zn)[Fe-2]O-4. In compounds which are s lowly cooled from 1200 degrees C to room temperature inversion is belo w detection limits. At T-N = 10.5 K the spinel exhibits long-range ant iferromagnetic order (LRO). The transition as seen in thermal-scan spe ctra by MS is very sharp. However, ND and mu SR experiments show that already at temperatures of similar to 10 T-N a short-range antiferroma gnetic ordering (SRO) develops which extends through similar to 70% of the sample volume just above T-N. Below T-N SRO and LRO coexist. At 4 .2 K still similar to 25% of the sample is short-range ordered. The re gions over which the SRO extends have a size of similar to 3 nm. Their fluctuation rates are in the GHz range. Modern ab initio cluster calc ulations successfully describe the magnetic hyperfine fields as well a s the electric field gradient (EFG) tensor at the Fe sites. Covalency of the Fe-O and Zn-O bonds is important. The physical origin of the re gions exhibiting SRO, however, remains unresolved at this point.