Abstract
In partially ordered magnets, order and disorder coexist in the same magnetic phase, distinct from both spin liquids and spin solids. Here, we determine the nature of partial magnetic ordering in the canonical frustrated antiferromagnet Gd2Ti2O7, in which Gd3+ spins occupy a pyrochlore lattice. Using single-crystal neutron-diffraction measurements in applied magnetic field, magnetic symmetry analysis, inelastic neutron-scattering measurements, and spin-wave modeling, we show that its low-temperature magnetic structure involves two propagation vectors (2-k structure) with suppressed ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental results are consistent with theoretical predictions of thermal fluctuation-driven order in Gd2Ti2O7, and reveal that inelastic neutron-scattering measurements on powder samples can solve the longstanding problem of distinguishing single-k and multi-k magnetic structures.
Highlights
Geometrical frustration is a central theme of condensed-matter physics because it can generate exotic magnetic states
These states can typically be divided into spin liquids, in which frustration inhibits long-range magnetic order, and spin solids, in which perturbations to the dominant frustrated interactions drive magnetic order[1]
Magnetic partial order can be driven by fluctuations in an “order-by-disorder” scenario[9], by interactions between emergent degrees of freedom in spin-fragmented states[10,11,12], or by proximity to a quantum critical point[13], while structural partial order can drive the behavior of materials such as fast-ion conductors[14,15], Pb-based photovoltaics[16,17], and high-pressure elemental phases[18]
Summary
Geometrical frustration is a central theme of condensed-matter physics because it can generate exotic magnetic states. The 2-k calculation reproduces well the experimental data, most importantly the prominent low-energy (~0.06 meV) mode that is absent for the other candidates This key qualitative observation is not affected by different choices of interaction parameters in the physically appropriate regime J > D ≫ J2. The 2-k structure has orthorhombic symmetry (magnetic space group Camcm), which is expected to drive a crystallographic distortion via spin-lattice coupling To test this hypothesis, we performed high-resolution powder neutron-diffraction measurements with ΔQ/Q = 5 × 10−5 on the HRPD instrument at ISIS46,47. Our data do not show visible peak splitting [Supplementary Fig. 2], and while a statistically significant rhombohedral distortion could be refined, orthorhombic refinements were inconclusive due to their increased number of parameters This suggests that spin-lattice coupling in Gd2Ti2O7 is too weak to yield an observable orthorhombic distortion in our measurements. Further experiments, such as NMR or Mössbauer spectroscopy, may allow the expected distortion to be observed, but the requirement for
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
