Complex metal oxides exhibit a wide range of useful properties such as high temperature super-conductivity, ferroelectricity, colossal magneto-resistance, magnetism, magneto-electricity, magneto-optical activity, and multiferroicity that have inspired spintronic, magnetoelectronic, and various optical applications.
MIT MRSEC researchers, have created both polycrystalline and single-crystal films of iron-substituted metal oxides that show room temperature magnetism and magneto-optical properties depending on the oxygen pressure at which the films are grown and their resultant oxygen composition. Optimized films were incorporated into an optical isolator device, which uses the magnetooptical properties of the material to control the flow of light in a photonic integrated circuit (see figure).
Diagram of an optical resonator that acts like a diode for light. Forward-propagating light is not resonant, and is transmitted. Backward light is resonant so is trapped in the ring and does not pass. The difference is due to the MO (magnetooptical) material in the resonator.
The understanding of how the oxygen content of complex metal oxides affects their magnetic properties and structure is expected to facilitate applications in new types of magnetic and optical devices. In particular, having an optically transparent magnetic material is useful in non-reciprocal optical devices such as an optical isolator in which light can be transmitted in one direction but blocked when traveling in the other direction. This is an essential component of photonic integrated circuits, protecting lasers from back-reflections. Other potential devices include circulators and magnetically-controlled optical modulators.
This work involved students in a multidisciplinary experiment, working with collaborators in Japan, Ireland, China and Chile on the synthesis, advanced characterization, and theoretical modeling of this rich material system.