Degree Year


Document Type

Thesis - Open Access

Degree Name

Bachelor of Arts


Physics and Astronomy


Yumi Ijiri


Nanoparticles, Halbach array, Superparamagnetism, Magnetic separation, Small angle x-ray scattering, Vibrating sample magnetometry, X-ray diffraction, Transmission electron microscopy, Structural characterization, Magnetic characterization


Magnetic nanoparticles have unique physical and chemical properties, making them appealing candidates for biomedical applications. These applications depend critically on size and magnetic uniformity of the nanoparticles. Unfortunately, very few purification methods exist to sort nanoparticles based on their magnetic properties. Here, we describe an unusual approach to this problem through our construction of a device containing a linear array of permanent magnets in a Halbach configuration, where successive magnet blocks have their magnetization orientation at right angles. The array provides a large region of relatively low magnetic field, yet high magnetic field gradient where sorting of nanoparticles based on their magnetic moment is possible. Using a flow channel for nanoparticle suspensions at an appropriate distance away from the array allows us to accumulate high moment nanoparticles against the channel wall, while low moment nanoparticles flow unaffected. We have demonstrated promising results on toluene-based iron oxide nanoparticles with diameters ~5 and 20nm, and water-based nanoparticles with diameters ~15nm and ~25nm, which we characterize using vibrating sample magnetometry and small- angle x-ray scattering. Future work includes a design that allows finer control of fields and gradients and testing with particles of same size but different magnetization.

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