Light-induced spontaneous magnetization in doped colloidal quantum dots.

An attractive approach to controlling spin effects in semiconductor nanostructures for applications in electronics is the use of light to generate, manipulate, or read out spins. Here, we demonstrate spontaneous photoinduced polarization of manganese(II) spins in doped colloidal cadmium selenide quantum dots. Photoexcitation generates large dopant-carrier exchange fields, enhanced by strong spatial confinement, that lead to giant Zeeman splittings of the semiconductor band structure in the absence of applied magnetic fields. These internal exchange fields allow spontaneous magnetic saturation of the manganese(II) spins to be achieved at zero external magnetic field up to approximately 50 kelvin. Photomagnetic effects are observed all the way up to room temperature.