Magnetic properties of the ZnFe2O4 spinel

Using neutron diffraction (ND), muon-spin rotation/relaxation (mu SR), and Fe-57 and Zn-67 Mossbauer spectroscopy (MS) we investigated magnetic properties of the normal spinel ZnFe2O4. Inversion is below limits of detection in samples which were slowly cooled from 1200 degrees C to room temperature. Below T-N = 10.5 K the spinel exhibits long-range antiferromagnetic order (LRO). However, already at temperatures of about T approximate to 10 T-N a short-range antiferromagnetic order (SRO) develops which extends through approximate to 70% of the sample volume just above T-N. Below T-N antiferromagnetic SRO and LRO coexist. At 4.2 K still approximate to 20% of the sample are short-range ordered. The regions exhibiting SRO are very small (approximate to 3 nm). Their fluctuation rates as estimated from mu SR are in the GHz range. For this reason the SRO above T-N remains hidden in MS and is only seen in ND and mu SR with their more appropriate time windows. Although the physical origin of the SRO remains an enigma, our experiments show that it is not caused by partial inversion but rather is an intrinsic property of ZnFe2O4. Modern ab initio cluster calculations successfully describe the magnetic hyperfine field as well as the electric field gradient tensor at the Fe site as seen by MS.