Study on crystallographic property in ferromagnetic Fe thin films using SHG

Abstract

In this thesis the surface structure of polycrystalline Fe films of 5, 50, 200 and 300 nm thickness on glass substrate are studied using a Ti:sapphire laser at 780 nm. We found that the surface structure possesses $C_s$ crystal structure pretty close to $C_{2v}$ through considering symmetry. We present one-fold intensity profile with one mirror plane in SH intensity as proof of $C_s$ symmetry. $C_s$ and $C_{2v}$ surface symmetry are usually showed at the (110) surface of cubic crystal. Therefore this surface would be related to bcc (110) growth orientation coinciding with XRD measurement. Further we treated surface SH asymmetry using Second-Harmonic Generation (SHG) method with various thickness. SH asymmetry increased with increasing thickness. For these results, it is concluded that the surface structure of very thin polycrystalline Fe film below 5 nm is almost isotropic, while in the case of the thicker Fe thin films, surface structure possesses the symmetry closer to $C_s$ structure close to $C_{2v}$.