Microscopic observation of magnetization response shaped by magnetic anisotropy in a single magnetic nanoparticle

Abstract Magnetization response under a magnetic field with thermal fluctuations is important for designing magnetic nanoparticles, which are extensively studied for biomedical applications. The magnetic properties of magnetic nanoparticles have conventionally been measured as net magnetization. In this study, the magnetization distribution in a single magnetic nanoparticle under a static magnetic field was observed using magnetic force microscopy. After the easy axis of the particle associated with magnetic anisotropy was aligned, the effects of magnetic anisotropy, the applied magnetic field, and thermal fluctuations on the magnetization orientation were analyzed. The single-particle magnetization response was then compared with the net magnetization response obtained from the static measurement and numerical simulations. The effects of magnetic moment and anisotropy energy on the magnetization distribution were evaluated by measuring single-core magnetic nanoparticles with different core diameters. Our measurement approach for magnetization response in a single magnetic nanoparticle also contributes to the analysis of the dipolar field affecting surrounding particles.