Influence of dislocations on magnetization processes in soft magnetic materials

Dislocations were introduced into specimens of Fe-3.25% Si alloys by plastic deformation and their density and distribution were controlled by annealing at various temperatures. Measurement of the coercive field H
c
, the initial susceptibility χ
i
, and the dislocation density N showed that H
c
varies as
\sqrt{N}
and χ
i
and
1/\sqrt{N}
. The temperature dependence of H
c
and χ
i
of deformed and undeformed specimens was investigated. The coercive field of undeformed specimens stays constant between -196° and 200°C and drop steadily at higher temperatures. The H
c
of deformed specimens increases to a maximum with rising temperature and then drops steeply near the Curie temperature. With an increase in the degree of deformation the maximum in H
c
occurs at lower temperature. The χ
i
-T behavior of the undeformed specimen measured between -196°C, and the Curie temperature exhibits a minimum around room temperature (RT) and a second minimum around 450°C. At the first maximum at 350°C the χ
i
achieves a magnitude of almost three times its RT value. With increasing deformation the first maximum is gradually flattened. During the isochronal annealing of the deformed specimens between 100°C and 800°C the H
c
and χ
i
remain constant up to about 200°C. Above this temperature the H
c
increases to a maximum and then drops gradually with rising temperature, while χ
i
drops to a minimum and then steadily increases with rising temperature. During the isothermal recovery at lower temperatures the H
c
exhibits an initial increase followed by gradual drop to lower values. The χ
i
drops initially to a minimum and then increases with annealing time.