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arXiv · 1505.07035

Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores

G. Sala·M. J. Gutmann·D. Prabhakaran·D. Pomaranski·C. Mitchelitis·J. B. Kycia·D. G. Porter·C. Castelnovo·J. P. Goff
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Abstract

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 Y2Ti2O(7-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.

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G. Sala, M. J. Gutmann, D. Prabhakaran, D. Pomaranski, C. Mitchelitis, J. B. Kycia, D. G. Porter, C. Castelnovo, J. P. Goff. 2015-05-26. Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores. https://doi.org/10.1038/nmat3924

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