Super-paramagnetic particles chemically bound to luminescent diamond: single nano-crystals probed with optically detected magnetic resonance

We have synthesized novel composite particles made of single-domain nanomagnets chemically bound to nanocrystals of diamond. Optically detected magnetic resonance spectra of nitrogen-vacancy centers in diamond allowed us to estimate the magnetic field of the nanomagnets and to observe the saturation of their magnetization when an external field of a few tens of mT has been applied. The saturation effect is in agreement with the size of the domains measured using transmission electron microscopy and a simple model of magnetization.