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 D_cr are determined so that above D_cr 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 D_cr < D ≤ D_c, and for vortex particles with diameters D > D_c, where D_c 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.