Magnetic Properties of Nanoparticle Assemblies
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Studies on system of magnetic nanoparticles with sizes in the nanometer scale have been the object of intensive research because of their many technological applications and unique magnetic properties that differ considerably from those of bulk materials. Nanometer magnetic particles exhibit specific properties such as superparamagnetism because of their very small sizes and fundamental change in the coordination, symmetry, and confinement. Superparamagnetism is regarded as a unique feature of magnetic nanoparticles and has great relevance to modern potential technologies including magnetic resonance imaging contrast agents, data lifetime in high-density information storage, and ferrofluid technology. However, because of the various contributions (i.e., magnetocrystalline, surface, shape, and dipolar anisotropy), the transition from superparamagnetic state to collective magnetic excitations (i.e., spin-glass) could occur in the interacting magnetic nanoparticles systems. The study on the mechanism of superparamagnetic properties in the system of fine magnetic particles will facilitate the control of superparamagnetic behavior and be favorable for their technological applications.