Structural 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 (thickness about 40 nm) fabricated by pulsed laser deposition. In the present article, x-ray diffraction and Mössbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation with a projected range positioned in the center of the films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (bcc) 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 to the bcc phase already by a dose of 5×1015 Cr/cm2, whereas the primitive orthorhombic phase of roughly equiatomic Fe–Cr alloys is about four times more resistant against ion bombardment. A five times higher Ne ion dose is required to induce the same transformation as by the Cr bombardment. The observed effects are discussed in view of radiation damage caused by the different ions and the grade of affinity of the initial phase to the bcc one.