J. Am. Chem. Soc. doi:10.1021/ja8098454 (2009)

Semiconductor nanoparticles, or quantum dots, should not be magnetic, yet some reports suggest that they are. Robert Meulenberg, currently at the University of Maine in Orono, Jonathan Lee at Lawrence Livermore National Laboratory in California and their co-workers present evidence that this magnetism comes from the chemical groups stuck to the dots' edges.

The group used X-ray magnetic circular dichroism and X-ray absorption spectroscopy to study the magnetic properties of electrons involved in chemical bonds in cadmium, one ingredient of cadmium–selenide quantum dots. The authors say these observations reveal that cadmium–selenide quantum dots are paramagnetic — their magnetism is induced and temporary — owing to interactions between cadmium and the chemical groups added to its surface to stifle its reactivity. The team saw no evidence to substantiate previous claims that quantum dots are ferromagnetic — that is, permanent magnets.