Nucleation at the first order phase transition in MnAs nanodisks

The first-order phase transition near 40◦C in as-grown thin epitaxial MnAs films prepared by molecular beam epitaxy on GaAs(001) and nanometer-scale disks fabricated from the same films is studied. The disks are found to exhibit a pronounced hysteresis in the temperature curve of the phase composition, i.e. supercooling and overheating take place in the disks whereas they are far less in the samples with continuous layers. These phenomena are explained in terms of the necessary formation of nuclei of the new phase in each of the disks independent from each other. The influence of the elastic strains in the disks is reduced considerably compared to the continuous layer.