Magneto-optic rotation and ellipticity of ultrathin ferromagnetic films

Magneto-optic rotation φ’ and ellipticity φ’ ’ values are reported as a function of thickness for 0–400 Å of bcc Fe(100) epitaxially deposited on Au(100) for both s- and p-polarized He-Ne laser light. The values are derived from a formula that connects φ’ and φ’ ’ with our recently reported longitudinal Kerr-effect measurements of ${\phi }_m$=(φ${\mathcal{’}}^2$+φ’ ${\mathcal{’}}^2$ ${)}^{1/2}$ and the parameters of two optical compensators that are used to convert ellipticity to rotation. The measurements were made in situ through an ultrahigh-vacuum window; our approach eliminates the effect of the window birefringence. The dominant contribution to ${\phi }_m$ reverses from being φ’ ’ in the ultrathin limit to being φ’ in the thick-film limit. Also, in the 0–30 Å range, the rotation remains near zero while the ellipticity increases linearly.