Magnetism of crystalline and nanostructured ZnFe2O4

We have investigated the magnetic properties of three differently prepared samples of the spinel ZnFe2 O-4 with mu SR, neutron diffraction, Mossbauer effect and magnetization measurements. Below T-N = 10.5 K, the first sample (annealed) shows long-range antiferromagnetic order in coexistence with sh ort-range magnetic order. The second sample (rapidly quenched) shows only s hort-range magnetic order. The third sample (nanostructured with an average particle size of about 9 nm) exhibits ferromagnetism below T-c approximate to 460 K combined with superparamagnetism. Below the blocking temperature of similar to 50 K the nanostructured sample exhibits a dependence on appli ed magnetic fields similar to that observed in spin glass systems. The role s of cation-site occupation and magnetic couplings in governing the differe nt magnetic behaviors exhibited by the samples are discussed. (C) 2000 Publ ished by Elsevier Science B.V. All rights reserved.