Magnetic Properties of Co II , Co III and Co II−III Coordinated to a Carbosilazane-Based Polymer

Abstract

Magnetization measurements have been performed on Co^II, Co^III and Co^II−III incorporated into carbosilazane-based polymeric matrix (PEDCSZ, –[(CH₃)₂SiNHCH₂CH₂NH]_n--). The local field effect has been evaluated using simple approach similar to the Weiss molecular field model in the paramagnetic state. In this approach, the exchange interaction is represented by the average molecular field constant g. The calculated g values are 327, 100, and 223 Oe-g/emu and the corresponding average molecular fields are: 2.7, 0.70 and 2.0 kOe for Co^II, Co^III and Co^II−III, respectively. The corresponding molecular field values are about four orders of magnitude lower than that in elemental Co metal. The magnetic measurements support the notion that coordination of this polycarbosilazane matrix with different valences of Co ions has pronounced effects on the exchange interaction and on the general magnetic properties of the system. The results also indicate that the strongest exchange effects are in the Co^II case, and that the magnetic properties in the mixed valance Co^{II- III} case do not follow the simple “Additive Rule”.

Keywords: Magnetization; Polycarbosilazane; Molecular field; Paramagnetism; Antiferimagnetism; Exchange interaction; Coordination and Magnetic moments.