An innovative mechanochemical method is reported for the in situ formation of crystalline metal-complexes on the surface of superparamagnetic nanocomposite microparticles. The process is demonstrated for coating Fe₃O₄ multicore–silica matrix particles with the 1,2,4-1H-triazole complex [ZnCl₂(TzH)₂]. The use of mechanochemistry demonstrates a flexible process to obtain functional shells on magnetic particle cores without the need for complicated surface-functionalisation reactions in solution. Simple mixing of the desired shell-precursors ZnCl₂ and 1,2,4-1H-triazole (TzH) with the magnetic particles in a ball mill is sufficient to tailor the particle surfaces with novel functionalities while retaining the superparamagnetic behaviour.