Synergy in Photomagnetic/Ferromagnetic <i>Sub</i>-50 nm Core-Multishell Nanoparticles

Based on nickel hexacyanidochromate and cobalt hexacyanidoferrate Prussian blue analogues, two series of photomagnetic/ferromagnetic <i>sub</i>-50 nm core multishell coordination nanoparticles have been synthesized in a surfactant-free one-pot multistep procedure with good control over the dispersity (10% standard deviation) and good agreement with the targeted size at each step. The composition and the valence state of each shell have been probed by different techniques that have revealed the predominance of Co<sup>II</sup>-NC-Fe<sup>III</sup> pairs in a series synthesized without alkali while Co<sup>III</sup>-NC-Fe<sup>II</sup> photoswitchable pairs have been successfully obtained in the photoactive coordination nanoparticles by control of Cs<sup>+</sup> insertion. When compared, the photoinduced behavior of the latter compound is in good agreement with that of the model one. Exchange coupling favors a uniform reversal of the magnetization of the heterostructured nanoparticles, with a large magnetization brought by a soft ferromagnetic shell and a large coercivity due to a harder photomagnetic shell. Moreover, a persistent <i>increase</i> of the photoinduced magnetization is observed for the first time up to the ordering temperature (60 K) of the ferromagnetic component because of a unique synergy.