Low-Energy Magnetic Excitations and Morphology in Layered Hybrid Perovskite−Poly(dimethylsiloxane) Nanocomposites

Hybrid organic−inorganic layered perovskites (R<INF>n</INF><INF></INF>NH<INF>3</INF>)<INF>2</INF>MnCl<INF>4</INF> of lyophilic aliphatic cations R<INF>n</INF><INF></INF>NH<INF>3</INF>⁺ (R<INF>n </INF><INF></INF>= C<INF>n</INF><INF></INF>H<INF>2</INF><INF>n</INF><INF></INF><INF>+1</INF>; n = 2, 9) have been studied for their potential as functional additives in poly(dimethylsiloxane) (PDMS). The evolution of the microstructure for various nanocomposite assemblies was characterized by means of X-ray diffraction and electron microscopy. Composites consisted of exfoliated MnCl<INF>4</INF> layers and enhanced aspect ratio crystallites composed of bundles of a few MnCl<INF>4</INF> sheets have been prepared. Such local morphology characteristics give rise to an inhomogeneous microstructure with enhanced surface areas and pronounced structural defects, suggestive of partial polymer intercalation only for the longer chain systems. The degree to which the two chemical realms interact at the interfacial regions does not affect the static magnetic properties. The composites display two-dimensional Heisenberg antiferromagnetic behavior (T<INF>N</INF> ≤ 42 K) similar to that in bulk powders. Electron paramagnetic resonance finds that the low-temperature spin dynamics of dispersed MnCl<INF>4</INF> layers are determined by the magnons and static solitons as in bulk materials. On the other hand, size-dependent features and local scale imperfections in the morphology, arising from the composite formation, soften the low-energy magnetic excitations of the pinned solitons. The interaction of PDMS and organocation chains affects the dynamics and the orientational ordering of the longer, linear alkylammonium molecules.