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In this paper, NiFe2O4 nanoparticles with average grain size of 12 nm were compacted into nanocrystalline materials under the pressure of up to 4.5 GPa. The Mossbauer spectra of NiFe2O4 nanocrystalline at room temperature show that the magnetic interaction and interface atomic state of nanocrystalline were influenced strongly by pressure. Under high pressure, the superparamagnetic relaxation of NiFe2O4 nanocrystalline were suppressed remarkably due to the enhancement of interparticle magnetic dipole interaction, and the degree of order of interface atoms was also improved gradually. At the same time, the information about the coordination polyhedron of interface atoms in NiFe2O4 nanocrystalline built under high pressure was provided by these Mossbauer spectra. (C) 2000 Elsevier Science S.A. All rights reserved.