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Long-lived photoinduced magnetization in copper-doped ZnSe–CdSe core–shell nanocrystals


Nanoscale materials have been investigated extensively for applications in memory and data storage. Recent advances include memories based on metal nanoparticles1, nanoscale phase-change materials2 and molecular switches3. Traditionally, magnetic storage materials make use of magnetic fields to address individual storage elements. However, new materials with magnetic properties addressable via alternative means (for example, electrical or optical) may lead to improved flexibility and storage density and are therefore very desirable. Here, we demonstrate that copper-doped chalcogenide nanocrystals exhibit not only the classic signatures of diluted magnetic semiconductors4—namely, a strong spin-exchange interaction between paramagnetic Cu2+ dopants and the conduction/valence bands of the host semiconductor—but also show a pronounced and long-lived photoinduced enhancement of their paramagnetic response. Magnetic circular dichroism studies reveal that paramagnetism in these nanocrystals can be controlled and increased by up to 100% when illuminated with above-gap (blue/ultraviolet) light. These materials retain a memory of the photomagnetization for hour-long timescales in the dark, with effects persisting up to 80 K.

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Figure 1: Cu-doped ZnSe–CdSe nanocrystals: a nanoscale diluted magnetic semiconductor exhibiting spd exchange.
Figure 2: Photo-induced enhancement of paramagnetization in Cu:ZnSe–CdSe nanocrystals.
Figure 3: Long-lived photoinduced magnetization in Cu-doped nanocrystals.
Figure 4: Influence of temperature, and a model of photoinduced paramagnetization.


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R.V., L.L., J.M.P., V.I.K. and S.A.C. are supported by the Chemical Sciences, Biosciences and Geosciences Division of the Office of Basic Energy Sciences, Office of Science, US Department of Energy. A.P. and S.B. acknowledge support from the Los Alamos LDRD programme.

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V.I.K., A.P., S.A.C. and S.B. conceived the study. A.P., R.V., L.L. and J.M.P. developed and synthesized the samples. A.P., S.B. and S.A.C. performed the measurements. A.P., S.B., V.I.K. and S.A.C. analysed the data and wrote the paper in consultation with all authors.

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Correspondence to V. I. Klimov or S. A. Crooker.

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Pandey, A., Brovelli, S., Viswanatha, R. et al. Long-lived photoinduced magnetization in copper-doped ZnSe–CdSe core–shell nanocrystals. Nature Nanotech 7, 792–797 (2012).

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