Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores

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.

(12 pages, 5 figures; Supplementary Information available from the journal website)

References in corpus (6)

• Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7
• Low Temperature Spin Freezing in Dy2Ti2O7 Spin Ice
• Observation of Magnetic Monopoles in Spin Ice
• Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique
• Spin Dynamics at Very Low Temperature in Spin Ice Dy${}_2$Ti${}_2$O${}_7$
• NMR relaxation in spin ice due to diffusing emergent monopoles

Cited by in corpus (6)

• Structural and Magnetic Investigations of Single-Crystals of the Neodymium Zirconate Pyrochlore, Nd2Zr2O7
• Role of defects in determining the magnetic ground state of ytterbium titanate
• Jammed spin liquid in the bond-disordered kagome Heisenberg antiferromagnet
• Magnetic Excitations in the Ground State of $\mathrm{Y}{\mathrm{b}}_2\mathrm{T}{\mathrm{i}}_2{\mathrm{O}}_7$
• Neutron Larmor diffraction investigation of the rare earth pyrochlores $R_2$Ti${}_2$O${}_7$ ($R$ = Tb, Dy, Ho)
• The monopole movement