Modified magnetic properties of paramagnetic (Zn,Mn)S at reduced dimensions P.J. Klar 1 , L. Chen 1 , W. Heimbrodt 1 , F.J. Brieler 2 , M. Fr¨ oba 2 , T. Kurz 3 , H.-A. Krug von Nidda 3 , and A. Loidl 3 1 Department of Physics and Materials Science Center, Philipps-University, Renthof 5, 35032 Marburg, Germany 2 Institute of Inorganic and Analytical Chemistry, Justus-Liebig University, Heinrich-Buff-Ring 58, 35392 Giessen, Germany 3 Experimentalphysik V, EKM, Department of Physics, University of Augsburg, Universit¨atsstraße 2, 86135 Augsburg, Germany Abstract. We present a novel way of synthesizing highly ordered arrays of mag- netic nanostructures with lateral dimensions of 2 to 10 nm by incorporation into mesoporous SiO 2 matrices. Such nanostructure arrays are suitable for studying magnetic phenomena at reduced dimensions, which is also important in the con- text of device miniaturization. Exemplarily we study (Zn,Mn)S nanowires. Changes of the macroscopic observables (e.g. Curie-Weiss parameter Θ and line width ΔH 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 Jnn and Jnnn) is not altered to a first approximation. The macro- scopic 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 consider- ably reduced compared to a Mn-ion in the bulk. Similar effects are also anticipated for antiferromagnetic and ferromagnetic wires. Our bottom-up approach of fabricating high-density ordered arrays of reg- ular magnetic nanostructures by incorporating them into the regular pores of SiO 2 matrices is very promising for studying magnetic properties of mag- netic semiconductors at reduced dimensions in the regime between 2 and 30 nm. The high density of nanostructures does not allow probing them in- dividually, but the amount of similar magnetic nanostructures is sufficient to employ almost any magnetic measurement technique. Furthermore, the well-defined pore diameter provides a sharp upper limit for the lateral exten- sion of the nanostructures. Moreover, in contrast to the other methods for synthesizing quantum wires, the lateral dimensions become better defined with decreasing diameter of the structures. Here, we will discuss exemplarily, the effects of reduced dimensions on the magnetic properties of paramag- netic (Zn,Mn)S nanostructures. However, this approach is extendable to any magnetic material, which can be synthesized inside the SiO 2 pore systems, including ferromagnets and antiferromagnets.