Structure and magnetic phase transformation in metastable Fe-Cr alloys induced by ion irradiation

Unusual metastable paramagnetic phases have been observed in Fe-Cr thin films fabricated by pulsed laser deposition. In the present paper, X-ray diffraction and Mössbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation. The projected range of the chosen implantation energies of 40 keV for Cr and 25 keV for Ne lies in the center of the about 40 nm thick films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (b.c.c.) structure depends on the initial phase of the film and the ion mass. The initial body-centered tetragonal phase which forms in the alloys with low Cr content (~30 at.%) can be completely transformed in the b.c.c. phase already by a dose of 5x1015 Cr/cm2 whereas the primitive orthorombic phase at roughly equiatomic Fe-Cr alloys is about 4 times more resistant against ion bombardment. One needs to apply a five times higher Ne-ion dose to induce the same transformation as by the Cr bombardment. The observed effects are discussed comparing the radiation damage caused by the different ions and the grade of affinity of the initial phase to the b.c.c. one.