Magneto-optical properties of Fe thin films in an external electric field*

Controlling magnetic properties by an external electric field ($E$-field) is a key challenge in magnetic physics. Previously, from first-principles calculations,\footnote{Nakamura, Shimabukuro, Fujiwara, Akiyama, Ito, Freeman, PRL{\bf 102}, 187201(2009); Nakamura, Akiyama, Ito, Weinert, Freeman, PRB{\bf 81}, 220409R(2010)} we demonstrated the $E$-field-driven magnetocrystalline anisotropy modification in Fe thin films and at the Fe/MgO interface. Here, we extend our investigations to treat the magneto-optical properties of Fe thin films in an $E$-field. Calculations were carried out using the film-FLAPW method\footnote{Wimmer, Krakauer, Weinert, Freeman, PRB{\bf 24}, 864(1981); Weinert, Wimmer, Freeman, PRB{\bf 26}, 4571(1982)},in which an $E$-field is incorporated and the conductivity tensor is obtained by applying the Kubo formula of linear response theory. Results predict that for an Fe monolayer, when the $E$-field is introduced over 1V/{\AA}, the calculated interband conductivity in the low energy region (less than about 2eV from $E_{\rm F}$) are modified compared to that in zero field, due to a magnetization reorientation from out-of-plane to in-plane. The calculated plasma frequency is also found to be reduced by 7\%, which suggests an $E$-field-driven magnetoresistance.