Strontium titanate (SrTiO 3) is a foundational material in the emerging field of complex oxide electronics. Although its bulk electronic and optical properties are rich and have been studied for decades, SrTiO 3 has recently become a renewed focus of materials research catalysed in part by the discovery of superconductivity and magnetism at interfaces between SrTiO 3 and other non-magnetic oxides. Here we illustrate a new aspect to the phenomenology of magnetism in SrTiO 3 by reporting the observation of an optically induced and persistent magnetization in slightly oxygen-deficient bulk SrTiO 3 crystals using magnetic circular dichroism (MCD) spectroscopy and SQUID magnetometry. This zero-field magnetization appears below ∼18 K, persists for hours below 10 K, and is tunable by means of the polarization and wavelength of sub-bandgap (400-500 nm) light. These effects occur only in crystals containing oxygen vacancies, revealing a detailed interplay between magnetism, lattice defects, and light in an archetypal complex oxide material.
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We thank D.L. Smith, Q. Jia, A.V. Balatsky and P. Littlewood for helpful discussions. Student support from M. Bayer (TU-Dortmund) is gratefully acknowledged. This work was supported by the Los Alamos LDRD program under the auspices of the US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering. Work at UMN supported in part by the NSF under DMR-0804432 and in part by the MRSEC Program of the NSF under DMR-0819885.