Modified Magnetic Properties of Paramagnetic (Zn,Mn)S at Reduced Dimensions

We present a novel way of synthesizing highly ordered arrays of magnetic nanostructures with lateral dimensions of 2 to 10 nm by incorporation into mesoporous SiO2 matrices. Such nanostructure arrays are suitable for studying magnetic phenomena at reduced dimensions, which is also important in the context of device miniaturization. Exemplarily we study (Zn,Mn)S nanowires. Changes of the macroscopic observables (e.g. Curie-Weiss parameter Theta and line width DeltaH of the electron paramagnetic resonance) of the paramagnetic phase due to reduced dimensions are observed. The microscopic coupling between the Mn-ions (e.g. the exchange constants J(nn) and J(nnn).) is not altered to a first approximation. The macroscopic modifications arise mainly due to geometrical restrictions, i.e. the number of neighbors in the cation shells around a Mn-ion in the surface region are considerably reduced compared to a Mn-ion in the bulk. Similar effects are also anticipated for antiferromagnetic and ferromagnetic wires.