The application your material is suited to depends on it's magnetic properties. Hard (high coercivity) magnetic nanoparticles are useful in very different ways to soft (low coercivity) magnetic particles. If they are micron sized it is likely that they are multi-domain rather than single domain, so may not be as useful as single domain or superparamagnetic magnetic nanoparticles. It also depends on what material the particles are made from, if they are toxic, if they are prone to oxidatation that might alter the magnetic properties, if they are coated in any capping agents, etc. There are a multitude of variables, so it is difficult to answer this question.
Have a think about the properties of your material, then you will have a better idea of what application it might be useful for.