Permanent magnet interface for magnetic circular dichroism spectroscopy

A rotatable magnet system for magnetic circular dichroism (MCD) studies has been designed. It employs permanent magnets and produces effective fields of 0.5-1.3 T depending on the design of magnets and poles. By revolving the magnet, reversing the direction of the field H, the difference spectrum (ϵ1-ϵr)+H-(ϵ1-ϵr)-H≈(ϵ1-ϵr)+2H can be obtained via a data processor. By accumulating such spectra, the signal to noise ratio is further improved. The difference procedure compensates for baseline drift and for the ordinary natural circular dichroism of an optically active sample. The MCD interface has an effective performance comparable to that of a superconducting magnet and is inexpensive to build and to run. It is easy to handle (weight 5-25 kg) and the leak field perturbations on photomultiplier and light source are negligible