5 nm nanocrystals of CoFe Prussian blue analogue totally exempt from any alkali cation were prepared. Their photomagnetic properties were compared to those of the corresponding powder made of 150 nm particles as well as to those of 5 nm nanocrystals of CoFe PBAs embedded in comparable silica matrices, made of Co II Fe III pairs and prepared under various conditions. The photomagnetic investigation of the nanoparticles exempt of any alkali cation clearly shows that they are transformed by light and the comparison of their photomagnetic properties to those of the powder made of particles of bigger size with the same chemical composition suggests that the species involved in the switching properties are surface species. Furthermore, the comparison of the magnetic properties of nanoparticles prepared under various conditions also suggests that the aggregation state of the nanoparticles in the porous channels of the silica matrix, by modulating inter-particle interactions, plays a predominant role in the magnetic properties of the nanoparticles assemblies.