ESR studies of MnO embedded into silica nanoporous matrices with different topology

Electron spin resonance (ESR) experiments were performed with antiferromagnetic MnO confined within a porous Vycor-type glass and within MCM-type channel matrices. A signal from confined MnO shows two components from crystallized and amorphous MnO and depends on the pore topology. Crystallized MnO within a porous glass shows a behavior having many similarities to the bulk. In contrast with the bulk, the strong ESR signal due to disordered "surface" spins is observed below the magnetic transition. With a decrease of the channel diameter, a fraction of amorphous MnO increases while the amount of crystallized MnO decreases. The mutual influence of amorphous and crystalline MnO is observed in matrices with a large channel diameter. In the matrices with a smaller channel diameter, the ESR signal mainly originates from amorphous MnO and its behavior is typical for the highly disordered magnetic system.