Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores

Gabriele Sala, Matthias Gutmann, D. Prabhakaran, D. Pomaranski, C. Mitchelitis, J.B. Kycia, Dan Porter, Claudio Castelnovo, Jon Goff

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The idea of magnetic monopoles in spin ice has enjoyed much success at intermediate temperatures, but at low temperatures a description in terms of monopole dynamics alone is insufficient. Recently, numerical simulations were used to argue that magnetic impurities account for this discrepancy by introducing a magnetic equivalent of residual resistance in the system. Here we propose that oxygen deficiency is the leading cause of magnetic impurities in as-grown samples, and we determine the defect structure and magnetism in Y2Ti2O7-δ using diffuse neutron scattering and magnetization measurements. These defects are eliminated by oxygen annealing. The introduction of oxygen vacancies causes Ti4+ to transform to magnetic Ti3+ with quenched orbital magnetism, but the concentration is anomalously low. In the spin-ice material Dy2Ti2O7 we find that the same oxygen-vacancy defects suppress moments on neighbouring rare-earth sites, and that these magnetic distortions dramatically slow down the long-time monopole dynamics at sub-Kelvin temperatures.
Original languageEnglish
Pages (from-to)488-493
Number of pages6
JournalNature Materials
Early online date13 Apr 2014
Publication statusPublished - May 2014

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