Dependence of Complex Magnetic Susceptibility on Alignment of Easy Axis in Magnetic Nanoparticles

Superparamagnetic nanoparticles have received significant attention with regard to medical applications of magnetic hyperthermia and magnetic nanoparticle imaging. For magnetic nanoparticles with uniaxial anisotropy, the coexistence of interwell and intrawell modes delays the magnetization response to the applied magnetic field. Therefore, an investigation of these two modes is essential for the study of magnetic moment dynamics. This study focuses on the frequency dependence of AC susceptibility to differentiate samples with varying degrees of easy axis alignment. The results indicate that the alignment of the easy axis separated the two modes of susceptibility. The variation in the activation energy depending on the degree of the easy axis alignment is also discussed, which clarifies the magnetization dynamics and Néel relaxation time of the magnetic nanoparticles.