Surface Spin Disorder in NiFe2O4 Nanoparticles

R. H. Kodama, A. E. Berkowitz, E. J. McNiff, Jr., and S. Foner
Phys. Rev. Lett. 77, 394 – Published 8 July 1996
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Abstract

Nickel ferrite nanoparticles exhibit anomalous magnetic properties at low temperatures: low magnetization with a large differential susceptibility at high fields, hysteresis loops which are open up to 160 kOe, time-dependent magnetization in 70 kOe applied field, and shifted hysteresis loops after field cooling. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. Implications of this model for possible macroscopic quantum tunneling in these materials are discussed.

  • Received 6 February 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.394

©1996 American Physical Society

Authors & Affiliations

R. H. Kodama and A. E. Berkowitz

  • Physics Department, University of California at San Diego, La Jolla, California 92093

E. J. McNiff, Jr. and S. Foner

  • Francis Bitter National Magnet Laboratory, Cambridge, Massachusetts 02139

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Vol. 77, Iss. 2 — 8 July 1996

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