Magnetic Langmuir−Blodgett Films of Bimetallic Coordination Nanoparticles of Cs0.4Ni[Cr(CN)6]0.9

Abstract

Magnetic Langmuir−Blodgett (LB) films of bimetallic coordination nanoparticles of the Prussian blue analogue Cs0.4Ni[Cr(CN)6]0.9 were prepared by using the adsorption properties of a monolayer of dioctadecyldimethylammonium bromide (DODA). The molecular organization of the DODA monolayer is strongly affected by the presence of the water-dispersable Cs0.4Ni[Cr(CN)6]0.9 nanoparticles in the subphase as has been shown by π−A isotherms and Brewster angle microscopy (BAM) images at the air−water interface. BAM images suggest that a layer of inorganic nanoparticles is adsorbed under the monolayer of DODA, for high surface pressure and medium concentration of nanoparticles in the subphase and for all surface pressures at high concentrations of nanoparticles. Transfer of the monolayer onto different substrates allowed the preparation of multilayers containing Cs0.4Ni[Cr(CN)6]0.9 nanoparticles. Magnetic properties of these LB films show a spin-glass-like behavior that can be explained by the strong magnetic dipolar interactions between the nanoparticles due to the small interparticle distances within the LB film. The magnetic properties of these LB films are very sensitive to the organization of the nanoparticles. They can be tuned by changing parameters such as the concentration of the subphase, the surface pressure, or the use of mixed monolayers. Thus, the Curie temperature of these LB films ranges from 60 K for the LB films prepared on the more concentrated subphase to 30 K for those prepared on the more diluted subphases. This is explained by the increase of interparticle distances and the subsequent weakening of the dipolar interactions between the nanoparticles within the LB film prepared on a subphase with a lower concentration of nanoparticles.