Synthesis and magnetic characterization of MnAs nanoparticles via nanoparticle conversion

We report on the synthesis of ferromagnetic manganese arsenide (MnAs) nanoparticles via the conversion of primary Mn particles which are generated in an aerosol process in a spark discharge generator. After sintering and size selection in an aerosol setup, the particles are deposited on GaAs(100)B and Si(111) substrates. Subsequent conversion to MnAs particles takes place in an annealing process under a hydrogen atmosphere with an arsine background pressure. The magnetic properties are studied using a SQUID magnetometer. The annealed MnAs particles exhibit hexagonal facets and show anisotropic magnetic behaviour on GaAs(100)B substrates, whereas on Si(111) they remain spherical and show isotropic magnetic behaviour. Scanning transmission electron microscopy studies are used to confirm the conversion from Mn to MnAs.