Speaker
Dr
Atieh Zamani
(Institute for Research in Fundamental Sciences (IPM))
Description
In recent years Fe1-xZrx (FeZr) Fe-rich metallic glasses (7 < x < 14), have been attracted considerable attention because of their striking magnetic properties. In this composition range, the addition of 1 at.% of Zr increases the Curie temperature in 20 K. However, the changes in behavior that could occur on the magnetic properties due to the structural evolution during the doping process is actually subject of discussion. The Curie temperature (Tc) of amorphous FeZr alloys can be greatly enhanced by doping with light elements. In this investigation, ion implantation is used to dope FeZr thin films with H, He, B, C, and N. We present a preliminary study of the structural evolution of the FeZr sample during the first steps of adding impurities.
The magnetic and local structural characterization from two experimental probes, SQUID magnetometry and X-ray absorption fine structure (EXAFS), are ideal experimental techniques to perfom this study. The conservation of the amorphous nature of the (FeZr) as-grown and implanted samples and the effect of incorporating dopant atoms in this structure is confirmed by EXAFS measurements on the Fe K-edge. EXAFS results indicate an almost negligible thermal expansion at temperatures below while normal thermal expansion takes place at higher temperatures. Such expansion seems to promote a reinforcement of the ferromagnetic interactions among Fe-Fe atoms that would account for the observed spontaneous increase in the magnetization as well as for the evolution of the coercive field.
Finding the correlation between the structure and the magnetic properties could, with the use of simple sphere-stacking models, allow us to create structures with desired magnetic properties. We found a shortening of the Fe-Fe bond when the Zr content was increased, which can explain the experimentally observed decrease in the magnetic moment and Curie temperature.
