Electric field biased Faraday rotation in multiferroic chromium-doped bismuth ferrite thin films

Multiferroics, materials which possess multiple ferroic orders, have seen a revival of interest in recent years as the need for multifunctional and multitunable devices has increased. A subset of multiferroics exhibit what is known as the magnetoelectric effect. The magnetoelectric effect is a generation of electric polarization via an applied magnetic field, and conversely the generation of magnetization due to an applied electric field. This particular effect is of interest due to the potential to control and tune devices by both electric and magnetic fields. Examining how this effect alters the magneto-optic response of the well-known multiferroic, BiFeO3 (BFO), could provide useful insight into how these multiferroics would function in optical devices. The Faraday rotation of a 10% Cr-doped BFO (111) thin film on an MgO substrate was measured for three conditions using an ac magnetic field technique: no biasing electric field, a positive 2 kV/m electric field, and a negative 2 kV/m electric field. The Verdet constant for these three conditions at an optical wavelength of 632.8 nm was 20.48 deg/kOe-cm, 21.25 deg/kOe-cm, and 2.01 deg/kOe-cm respectively. These results demonstrate the possibility to manipulate the magneto-optic response of the thin film with an external dc electric field. This low magneto-optic response is due primarily to the still relatively weak magnetization of the BFO thin film, as well as its high optical absorption further enhanced by the Cr-doping. Future work to both overcome these deficiencies and investigate how precisely the magneto-optic response can be controlled by an external field is presented and discussed.