Remagnetization kinetics of soft ferrogels

Abstract

We present the results of the theoretical analysis of remagnetization kinetics and magnetic hyperthermia effect in a single-domain ferromagnetic particle embedded in a soft elastic-viscous medium (gel or biological tissue for example). Unlike previous studies, we consider simultaneous action of both main mechanisms of particle remagnetization in an alternating magnetic field. Namely, (i) its body turn (rotation) with its magnetic moment and (ii) the Neel remagnetization through the potential barrier of the particle magnetic anisotropy. We suppose that the energy of the particle Zeeman interaction with the field is less than the energy of the anisotropy; no other restrictions on the field strength are assumed. In the linear, with respect to this field, approximation, the frequency dependences of the real and imaginary parts of the particle complex susceptibility are calculated in more details. The real part monotonic decreases with the field frequency. If the host medium is rigid enough, the imaginary part of the susceptibility has a maximum, corresponding to the Neel relaxation. In the soft system, it has maximum, reflecting the particle rotation in the field. In the intermediate case, our calculations demonstrate two maximums of the imaginary part. We hope the present results will be useful for the development of scientific basement of magnetic hyperthermia therapy of oncological diseases.