We have studied the paramagnetic-to-antiferromagnetic phase transition in spherical $\beta \text{-MnS}$ nanoparticles of well defined diameters in the range of 3–11 nm. The MnS nanoparticles were obtained by intrapore synthesis inside mesoporous silica matrices. Electron spin resonance and magnetization measurements reveal that no antiferromagnetic order is established in MnS spheres of 3 nm down to 2 K and that the antiferromagnetic order is gradually recovered on increasing the particle diameter to 11 nm. Photoluminescence excitation spectroscopy proves that in all MnS nanostructures the nearest-neighbor coupling between the Mn ions remains the same as in bulk suggesting that the suppression of the phase transition arises due to geometric restrictions alone.

• Received 25 August 2008

DOI:https://doi.org/10.1103/PhysRevB.78.132408