Speaker
Description
Pyrochlore Heisenberg antiferromagnets (HAFs) are commonly studied as an archetypal example of three- dimensional geometrical magnetic frustration. The study of these so-called “highly frustrated magnets” provides a route to access a large variety of fascinating emergent low-temperature magnetic states including spin-liquids, spin-glasses, spin-ices, and fragmented spin-structures.
Gd-pyrochlores should, in principle, be rather simple examples of pyrochlore HAFs due to the spin-only ground state of Gd$^{3+}$. However, dipolar interactions, and admixed orbital states, result in a variety of magnetic ground states ranging from the co-planar Palmer--Chalker (PC) state, to fascinating partially ordered multi-k structures.
We will present spin-wave studies on 3 examples of Gd-pyrochlore HAFs, Gd$_2$Ti$_2$O$_7$ (GTO) [1], Gd$_2$Sn$_2$O$_7$ (GSO) [2] and Gd$_2$Pt$_2$O$_7$ (GPO) [3]. GSO and GPO are uncontroversial PC magnets, where powder TOF-INS measurements on isotopically substituted samples elucidate the leading magnetic interactions. In the case of GTO, analysis of the spin-wave spectra, even in a powder sample, is found to solve the multi-k problem - where (even single crystal) diffraction cannot decide between mutli-k variants, but the ground state excitations are decisive in this regard.
[1] J A M Paddison, et al., Suppressed-moment 2-k order in the canonical frustrated antiferromagnet Gd2Ti2O7. npj Quantum Materials, 6(1), 99 (2021). https://doi.org/10.1038/s41535-021-00391-w
[2] J R Stewart, et al.,. Collective dynamics in the Heisenberg pyrochlore antiferromagnet Gd 2Sn2O7. Physical Review B, 78(13), 3–6 (2008). https://doi.org/10.1103/PhysRevB.78.132410
[3] P G Welch, et al., Magnetic structure and exchange interactions in the Heisenberg pyrochlore antiferromagnet Gd2Pt2O7. Phys. Rev. B, 105(9), 094402. (2022) https://doi.org/10.1103/PhysRevB.105.094402
