Geometric Magnetic Frustration in Double Perovskite Oxides A2BB'O6

Speaker: 
Jeremy Carlo (Villanova)
Event Date and Time: 
Thu, 2015-07-30 14:00 - 15:00
Location: 
TRIUMF Auditorium


Geometric magnetic frustration occurs when the spatial arrangement of magnetic moments inhibits the development of magnetic order. This is most commonly associated with antiferromagnetic correlations on triangular or tetrahedral lattices, and manifests in a variety of structures including the Kagome, spinel, pyrochlore, garnet and face-centered cubic lattices. Frustration typically results in a vast degeneracy of ground states, which may be broken by a number of mechanisms ranging from prosaic to exotic, or remain unbroken down to T=0, resulting in a quantum spin liquid. Frustrated systems are thus characterized by rich phase diagrams featuring diverse ground states, often driven by exotic physics due to the cancellation of normally more dominant terms in the Hamiltonian, and as a result frustration has attracted substantial research interest from the community.

I will give a brief overview of the physics of frustrated systems, and then concentrate on our studies of frustration in rock-salt-ordered double perovskite oxides, A2BB'O6. In these systems, magnetic B' cations are arranged on a FCC lattice, or equivalently a lattice of edge-sharing tetrahedra. Due to the versatility of the perovskite structure, such compounds can be generated with elements ranging across the entire periodic table, with structural disorder, ionic radius, lattice parameter, and moment size among the many degrees of freedom one can adjust in order to test aspects of frustration physics. I will discuss our results on several such systems, prepared with 4d and 5d ions which add sizable spin-orbit coupling. These include the spin-singlet Ba2YMoO6 (4d1 Mo5+), the gapped long-range antiferromagnet Ba2YRuO6 (4d3 Ru5+), and the contrasting behaviors in the isostructural 5d2 "doppelganger" systems Ba2YReO6 and Ba2CaOsO6, making use of inelastic neutron scattering and muon spin relaxation, powerful particle-beam techniques performed at large-scale accelerator and reactor sources, capable of providing unique and complementary information regarding structure and magnetism.

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