Bistable spin-crossover nanoparticles showing magnetic thermal hysteresis near room temperature

We have demonstrated that the reverse micelle technique can be applied to polymeric spin-crossover systems, such as [Fe(Htrz)2(trz)](BF4), to control the growth of the crystallites. Small nanoparticles of diameters around 10 nm and narrow size distribution were obtained. It is easy to envision that, by modifying the synthetic procedure, the size and critical temperatures of these nanoparticles can be tuned. On one hand, different ratios of solvent, water, and surfactants will lead to different micelle sizes, which will affect the particle size and, maybe, the magnetic properties. On the other hand, the critical temperatures can be lowered towards room temperature by changing the composition of the nanoparticles. Indeed, on doping the [Fe(Htrz)2(trz)](BF4) nanoparticles with 20%ZnII, the thermal reversible hysteresis loop moves to Tc↑∼356 K and Tc↓∼336 K.Spanish Ministry of Education and Science (MEC) (Projects CTQ2005-09385-C03-01 and MAT2004-3849