Swift iodine ion modification of the structural and magnetotransport properties of Fe/Cr systems

Abstract Fe/Cr/Fe trilayers and (Fe/Cr) 20 multilayers prepared under ultrahigh vacuum conditions by thermal evaporation were irradiated with 200 MeV I 13+ ions in the fluence range between 1 × 10 11 and 8 × 10 12  I/cm 2 . The structural properties of the Fe/Cr/Fe trilayers and (Fe/Cr) 20 multilayers were measured by X-ray reflectivity (XRR) and conversion electron Mossbauer spectroscopy (CEMS). Magnetic exchange coupling between the Fe layers through the Cr spacer layer was observed by SQUID magnetization measurements. Magnetoresistance effect was measured using four probe method at room temperature. The XRR spectra showed an increase of the interface roughness versus increasing irradiation fluence in the multilayers, while in the trilayers smoothening of the interfaces in the sample irradiated with fluence equal to 4 × 10 11  I/cm 2 and very slight change for other fluences were observed. Improving of the interface structure in the trilayers at this fluence was observed also by CEMS. Moreover the Mossbauer spectra also confirm roughening of the interfaces as a function of fluence for multilayers. Before irradiation an antiferromagnetic coupling fraction dominated in all samples. After irradiation the changes of magnetic coupling were different in both types of samples. The trilayers were less sensitive to the irradiation fluence than multilayers and an increase of the antiferromagnetic fraction at small fluences was observed. In the multilayers a continuous decrease of the antiferromagnetic fraction as a function of fluence was evidenced. Vanishing of the antiferromagnetic coupling, observed for the largest fluence, resulted in the decrease of magnetoresistance effect in the Fe/Cr multilayers.