Magnetization Processes in Non-Single Domain Magnetite Particles

Quasi-static hysteresis loops of spherical and spheroidal magnetite nanoparticles with semi-axes ratio a/b = 1.5 and 2.0 with different types of combined magnetic anisotropy are calculated using numerical simulation. For particles of each type the critical diameters Dcr are determined so that above Dcr the magnetization curling becomes the easiest mode of particle magnetization reversal. The hysteresis loops are calculated both for single-domain nanoparticles in the diameter range Dcr < D ≤ Dc, and for vortex particles with diameters D > Dc, where Dc is the single-domain diameter. The results obtained are compared with the hysteresis loops of single-domain particles with uniform magnetization rotation. The remanent magnetization and coercive force of oriented and non-oriented dilute assemblies of magnetite nanoparticles with different aspect ratios are determined as the functions of the transverse particle diameter.