PHYSICAL REVIEW B VOLUME 53, 9143 (1996)
W. Schiessl, W. Potzel, H. Karzel, M. Steiner, G. M. Kalvius, A. Martin, M. K. Krause, I. Halevy and J. Gal, W. Schäfer, G. Will, M. Hillberg, R. Wäppling
Abstract
Using neutron diffraction (ND), muon-spin rotation/relaxation ( mSR), and 57Fe and 67Zn Mössbauer 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 °C to room temperature. Below TN = 10.5 K the spinel exhibits long-range antiferromagnetic order (LRO). However, already at temperatures of about TN » 10TN a short-range antiferromagnetic order (SRO) develops which extends through »70% of the sample volume just above TN. Below TN antiferromagnetic SRO and LRO coexist. At 4.2 K still » 20% of the sample are shortrange ordered. The regions exhibiting SRO are very small ( » 3 nm). Their fluctuation rates as estimated from mSR are in the GHz range. For this reason the SRO above T N remains hidden in MS and is only seen in ND and mSR 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.
