The Fe₅₀Pt₅₀ alloy exhibits remarkable magnetic properties related to its crystalline phase L1₀, which looks like a millefeuille “pastry” of pure iron and platinum layers. We know how to chemically synthesize FePt nanoparticles surrounded by organic ligands that prevent their aggregation in liquid phase. But, Fe and Pt atoms are in disorder and the particles have no permanent magnetization. How to put these in order? By heating at 700°C. The unacceptable side effect: the organic ligands are destroyed and the particles aggregate! So, we physically separate the particles before the heat treatment on inert and stable grains of... salt! Upon exiting the oven, the nanoparticles are indeed in the L1₀ phase with good magnetic properties and remain isolated from each other by salt. But, how do you get them back?

If we dissolve our salty millefeuille “pastry” in water, the particles aggregate together and we do not win much. So we do it in an aqueous solution of cysteine. Inedible, you say! True, but thanks to its S-H thiol function, cysteine binds tightly to the surface of FePt. Our particles are well-dispersed again, and have the same properties as in their salty matrix. The cysteine ligand is not the most suitable for applications, but we managed to substitute a posteriori other ligands best suited to the surface functionalization while keeping independent nanoparticles. Molecular gastronomy thus offers other opportunities than the mere pleasure of the taste buds!