Growth mechanism and magnetic properties of AlMn metastable phase formed by ion beam mixing

Abstract

The kinetics of ion beam mixing and the growth mechanism of metastable phases have been investigated for the Al-Mn system. It is revealed that the residual diffusive motion induced by a collision cascade is the decisive factor for metastable phase formation. The residual diffusivity depends strongly on the substrate temperature during ion irradiation. Its relaxation time at temperatures of 350–550 K is estimated to be of the order of 10 −7−10 −6 s. More rapid quenching produces an amorphous phase, whereas slower cooling leads to thermally stable phases. The metastable τ phase with ferromagnetism is formed directly by ion beam mixing in the above temperature range. The dependences of mixing temperature and ion dose on the magnetic properties are accounted for by the kinetics of ion beam mixing and the induced internal stress. Finally, a model describing the ion beam mixing effect is proposed.