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When a piece of a magnetic material is made smaller and smaller, is acquires simpler magnetic domain structure since less domain walls are needed in order to minimize the stray field energy. The extreme limit is represented by single domain particles. Below a size of about 500 nm it is no more energetically favorable to form many domains. A further reduction of the size leads to single domain particles. Nanoparticles offer exciting opportunities for technologies at the interfaces between chemistry, physics and biology. Their appeal stems not only from their use as single particles, but also from their potential to form self-organized films and solids. Magnetic nanoparticles are useful for a wide range of applications from data storage to medicinal imaging.
High capacity information storage, for instance, requires smaller particle size that decreasing the particle size lowers the anisotropy energy responsible for holding the magnetic moments along certain directions and it becomes comparable to the thermal energy. Thermal fluctuations randomize magentic moments (unless external magnetic field is applied), which is the essence of the so-called superparamagnetic behavior. Core/shell structured magnetic systems have an extra source of anisotropy that increases the stability of magnetic moments up to certain temperature called blocking temperature. Increasing the blocking temperature as close as possible to room temperature as we keep the particle size small is the main challenge in this field.
Current magnetic-nanoparticle technology is challenging due to the limited magnetic properties of iron oxide nanoparticles. Increasing the saturation magnetization of magnetic nanoparticles may permit more effective development of multifunctional agents for simultaneous targeted cell delivery, magnetic resonance imaging contrast enhancement, and targeted cancer therapy in the form of local hyperthermia. Delaware researchers have recently synthesized novel iron-based nanoparticles (FeNPs) coated with biocompatible bis-carboxyl-terminated poly(ethylene glycol) (cPEG). In comparison to conventional iron oxide nanoparticles similar in size (10 nm), FeNPs particles have a much greater magnetization and coercivity based on hysteresis loops from sample magnetometry. Next-generation FeNPs with a biocompatible coating may in the future be functionalized with the attachment of peptides specific to cancer cells for imaging and therapy in the form of local hyperthermia.
Campus-wide Interdisciplinary Collaboration:
- Yan Jin (Dept. of Plant and Soil Sciences)
- Core/shell structured and ferrite particles for magnetic recording (Hadjipanayis, Shah)
- Nanoparticle fabrication by sol-gel technique (Shah)
- Collective behavior of magnetic nanoparticles (Unruh)
- Biological applications of magnetic nanoparticles (Xiao, Jin)
- Medical applications of magnetic nanoparticles (Hadjipanayis).