26 March 1999 Ž . Chemical Physics Letters 302 1999 523–527 A Langmuir–Blodgett film presenting a ferromagnetic state below 25 K C. Lafuente, C. Mingotaud ) , P. Delhaes Centre de Recherche Paul Pascal–CNRS, AÕenue A. Schweitzer, F-33600 Pessac, France Received 5 October 1998; in final form 29 January 1999 Abstract A positively charged monolayer spread on a sub-phase containing copper hexacyanoferrate leads to hybrid inorganic– organic LB films. Those multilayers present a spin ordering below 25 K. The Curie temperature of the LB films is found to be independent of the multilayer thickness. Their magnetization is clearly proportional to the number of transferred layers, demonstrating that the deposition process is perfectly regular. These results show that a bulk ferromagnetic behavior can be observed in this hybrid material, even if the distance between magnetic layers is considered as large. q 1999 Elsevier Science B.V. All rights reserved. 1. Introduction The search for new materials with useful elec- tronic and magnetic properties has led to the prepara- tion of hybrid organicrinorganic entities where both components mix their properties in the molecular assembly. One way to build these materials is given Ž . by the Langmuir–Blodgett LB technique. Indeed, a charged amphiphilic monolayer can be used as tem- plate to organize inorganic materials by adsorption of ionic species along the interface. This strategy has been successfully employed to prepare LB films containing inorganic compounds like Keggin polyox- wx wx wx ometalates 1 , oxalato 2 or cyano 3 complexes. With the aim to prepare LB films presenting cooperative magnetic phenomena, one may be inter- ) Corresponding author. Fax: q33 5 56 84 56 00; e-mail: mingotaud@crpp.u-bordeaux.fr ested in the Prussian Blue-like compounds. They w Ž . x have the general formula A B CN P nH O where k 6 l 2 A and B are transition metallic ions, respectively, in a high- and low-spin state. In this system, the CN ligands act as a good mediator for magnetic interac- tions. Finally, they show a ferri or a ferromagnetic behavior at various Curie temperatures, which have wx been found as high as 310 K 4 . Ž Recently, we used Prussian Blue i.e. Fe - 4 w Ž . x . Fe CN P 12H O dissolved in the sub-phase to 6 3 2 build the first LB film presenting a ferromagnetic Ž . state - T s 5.7 K . Indeed, a monolayer of dimeth- c Ž . yldioctadecylammonium salt DODA spread on such a sub-phase leads, after transfer onto a solid sub- strate, to multilayers in which the inorganic part has Ž . a thickness perfectly defined a few angstrom and presents an anisotropic behavior as was demon- wx strated by ESR and SQUID measurements 5 . An extension of this Prussian Blue study to other mixed-valence cyanide compounds is the objective 0009-2614r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0009-2614 99 00158-X