I am a postdoctoral research fellow in the Swager group, at MIT. My research explores the use of organic (carbon-containing) molecules to prepare materials with new function. The attraction of such materials is that they can be flexible – like plastics – and so deformable and mouldable into useful structures. It is also relatively easy to control the structure of a molecule, opening up avenues towards the design of bespoke materials.
Recently, I have been exploring a magneto-optic property called Faraday rotation. This effect was discovered in the 1800s by Michael Faraday, and describes the change of the polarization of light as it passes through a material in the presence of a magnetic field.
The strength of the Faraday rotation is described by the Verdet constant (V), which varies as a function of light wavelength, and which can be positive or negative. In this respect, it is similar to a circular dichroism or optical rotatory dispersion spectrum.
Materials with strong Faraday rotation are currently used for the control of light (e.g. optical isolators and optical circulators), and can also be used as sensitive photonic magnetic field sensors. The current predominant materials are inorganic rock-like materials: ferrimagnetic garnets. For example, terbium gallium garnet (TGG) has a Verdet constant of about 10,100 deg/Tm at 532 nm. These materials have net unpaired electrons, which provide an intuivite explanation for their strong interactions with magnetic fields.
It has recently been discovered that some polymers, including regioregular polythiophene, exhibit Verdet constants of the same order of magnitude as that of TGG. This discovery is spectacular: these polymers are diamagnetic (or have very dilute spin contamination), yet interact strongly with a magnetic field.
My work seeks to understand why this effect arises in organic materials, and to deduce design principles for new magneto-optic materials. The goal is to be able to prepare flexible magnetic field sensors suitable for incorporation into devices.
Practically, I have designed and constructed a magneto-optic spectrometer in several designs, and am in the process of preparing and testing small molecules and polymers for their Faraday rotation.