  Magnetic vortices existing in soft magnetic nanoparticles with sizes larger
than the single-domain diameter can be efficient nano-heaters in biomedical
applications. Using micromagnetic numerical simulation we prove that in the
optimal range of particle diameters the magnetization reversal of the vortices
in spherical iron and magnetite nanoparticles is possible for moderate
amplitudes of external alternating magnetic field. In contrast to the case of
superparamagnetic nanoparticles, for the vortex configuration the hysteresis
loop area increases as a function of frequency. So that high values of the
specific absorption rate, on the order of 1 kW/g, can be obtained at a
frequency 1.0 MHz. Because the diameter D of a non single-domain particle is
several times larger than the diameter d of a superparamagnetic particle, the
volume of heat generation for the vortex turns out to be many times larger.
This shows the advantage of vortex configurations for heat generation in
alternating magnetic field in biomedical applications.
