title: Tuning size and thermal hysteresis in bistable spin crossover nanoparticles.
abstract: Nanoparticles of iron(II) triazole salts have been prepared from water-organic microemulsions. The mean size of the nanoparticles can be tuned down to 6 nm in diameter, with a narrow size distribution. A sharp spin transition from the low spin (LS) to the high spin (HS) state is observed above room temperature, with a 30-40-K-wide thermal hysteresis. The same preparation can yield second generation nanoparticles containing molecular alloys by mixing triazole with triazole derivatives, or from metallic mixtures of iron(II) and zinc(II). In these nanoparticles of 10-15 nm, the spin transition "moves" towards lower temperatures, reaching a 316 K limit for the cooling down transition and maintaining a thermal hysteresis over 15-20-K-wide. The nanoparticles were characterized by dynamic light scattering, TEM, and AFM, after deposition on gold or silicon surfaces. The spin transition was characterized by magnetic susceptibility measurements and EXAFS (in solid samples after solvent removal) and also by the color change between the LS (violet) and HS (colorless) states in an organic solvent suspension. The discovery of bistable magnetic nanoparticles of 6 nm with a wide thermal hysteresis above room temperature showcases the actual possibilities of spin crossover materials for nanotechnological applications.
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Av. Paisos Catalans, 16, 43007-Tarragona, Spain.
authors.forename: José Ramón
authors.initials: JR
authors.lastname: Galán-Mascarós
authors.forename: Eugenio
authors.initials: E
authors.lastname: Coronado
authors.forename: Alicia
authors.initials: A
authors.lastname: Forment-Aliaga
authors.forename: María
authors.initials: M
authors.lastname: Monrabal-Capilla
authors.forename: Elena
authors.initials: E
authors.lastname: Pinilla-Cienfuegos
authors.forename: Marcelo
authors.initials: M
authors.lastname: Ceolin
mesh_terms: D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D013696:Temperature; D014230:Triazoles / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D005296:Ferrous Compounds; D014230:Triazoles; D014867:Water