New system for measuring magnetic after-effect: application to nickel ferrite

An automatic system for measuring magnetic viscosity in bulk materials base d on an inductive technique has been developed. The system allows to study the magnetization variation when the magnetic field is suddenly changed. Th e system procedure provides a set of isothermal curves in the range 77 < T( K) < 400. In order to study the temperature dependence of the relaxation ph enomena from the isothermal curves, the isochronal spectrum is obtained. Me asuring the after-effect of nickel ferrite samples tests the capability of our system. The obtained spectra show a relaxation process between 250 and 350 K. The dependence of this relaxation process on the amplitude of the ex ternal magnetic field is also analyzed. (C) 2001 Elsevier Science B.V. All rights reserved.