An X-ray-induced insulator–metal transition in a magnetoresistive manganite

Manganese oxides of the general formula A1–xBxMnO3 (where A and B are trivalent and divalent cations, respectively) have recently attracted considerable attention by virtue of their unusual magnetic and electronic properties1–9. For example, in some of these materials magnetic fields can drive insulator-to-metal transitions where both the conductivity and magnetization change dramatically—an effect termed 'colossal magneto-resistance'1–3—raising hopes for application of these materials in the magnetic recording industry1–9. Here we show that in one such compound, Pr0.7Ca0.3MnO3, a transition from the insulating antiferromagnetic state to the metallic ferromagnetic state can be driven by illumination with X-rays at low temperatures (<40 K). This transition is accompanied by significant changes in the lattice structure, and can be reversed by thermal cycling. This effect, undoubtedly a manifestation of the strong electron–lattice interactions believed to be responsible for the magnetoresistive properties of these materials6–9, provides insights into the physical mechanisms of persistent photoconductivity, and may also find applications in X-ray detection and X-ray lithographic patterning of ferromagnetic nanostructures.