Spin Correlations in the Geometrically Frustrated Pyrochlore Tb2Mo2O7

Deepak Singh, Physics, MIT

Geometrically frustrated magnets hold great interest in the condensed matter physics community, as they often exhibit unusual physical properties. The compound we study, Tb2Mo2O7, stands at an interesting crossroads, being a representative of both the Mo-based pyrochlores and the Tb-based pyrochlores. The Mo-based compounds exhibit a metal-insulator transition between ferromagnetic metal states to spin glass insulators. The pyrochlore compound, TbMoO, crystallizes in a cubic space group in which both the Tb and Mo atoms form three-dimensional networks of corner-sharing tetrahedrons. Thus, each magnetic ion resides on a highly frustrated pyrochlore lattice. In this talk, I will report the neutron scattering studies of the spin correlations of the geometrically frustrated pyrochlore TbMoO using single crystal samples. Magnetic susceptibility measurements confirm the spin-glass transition below T~ 24 k, similar to that observed in previous powder samples. Diffuse elastic peaks are observed at low temperatures, indicating short-range ordering of the Tb moments in an arrangement where the Tb moments are slightly rotated from the preferred directions of the spin ice structure. In addition, a Q-independent signal is observed which likely originates from frozen, but completely uncorrelated, Tb moments. I will also discuss inelastic measurements on both single crystal and powder samples exhibiting the absence of sharp peaks due to crystal field excitations. These results will shed new lights on the understanding of the physics of Tb sublattice in this compound.

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