title: Magnetic behaviour of nickel-cyclam complexes in mesoporous silica: EPR investigations.
abstract: Electron paramagnetic resonance (EPR) investigations are carried out on mesoporous silica (SBA15) functionalized by Ni-cyclam complexes (1,4,8,11-tetraazacyclotetradecane groups chelating nickel ions). The magnetic behaviour of nickel-cyclam groups, their mutual interactions and dispersions in the mesoporous silica are compared with respect to the doping rates and the synthesis procedures. The spin-spin interactions and the relaxation processes were clarified from the thermal evolution in the temperature range (4 K, 300 K) of the paramagnetic spin susceptibilities and EPR line widths. Thus, the relaxation mechanisms seem marked by the Jahn-Teller effect on the nickel ions mediated by exchange interactions between nearest spins. Isolated Ni-cyclam molecules are involved in some samples while others show the formation of clusters where phonon-assisted one-dimensional (1D) ferromagnetic ordering occurs below 45 K. The performed experiments point out the efficiency of the EPR technique to probe the degree of functionalization of mesoporous silica by Ni-cyclam molecules and to give valuable feedback to improve the synthesis routes.
authors.affiliation: Laboratoire de Physique de l'Etat Condensé LPEC, UMR CNRS no 6087, Université du Maine Avenue Olivier Messiaen 72085, Le Mans CEDEX 9, France. Institut de Recherche en Ingénierie Moléculaire et Matériaux Fonctionnels IRIM2F, FR CNRS no 2575, France. Institute of Physics, Jan Dluogosz University, Aleja Armii Krajowej 13/15, 42-200 Czestochowa, Poland.
authors.forename: L
authors.initials: L
authors.lastname: Laskowski
authors.forename: A
authors.initials: A
authors.lastname: Kassiba
authors.forename: M
authors.initials: M
authors.lastname: Makowska-Janusik
authors.forename: A
authors.initials: A
authors.lastname: Mehdi
authors.forename: A
authors.initials: A
authors.lastname: Gibaud
authors.forename: N
authors.initials: N
authors.lastname: Errien
authors.forename: J
authors.initials: J
authors.lastname: Swiatek