Magnetically tunable optical absorbance in a colloidal system

We study the optical absorbance from a magnetically arranged colloidal structure, and investigate the possibility of creating a magnetically controlled optical sensor using this system. The colloids form chains when exposed to an external magnetic field, which tend to collapse and form a more random particle arrangement when the field is removed. We show that a small magnetic field is able to change the sensor's reflection coefficient by more than 30%, and investigate in detail the relaxation mechanism when the field is turned off.