Magnetic Studies of the Spin Liquid and Spin Ice Pyrochlores

J. S. Gardner
NRC Canada, Chalk River Laboratories, Stn. 18, Chalk River, ON, K0J 1J0.

Antiferromagnetically coupled spins residing on a network of corner sharing triangles (Kagome lattice) or tetrahedra (pyrochlore lattice) have attracted much attention in recent years and often display phenomena known broadly as geometrical frustration. Because of their low propensity to order, even for classical spins, antiferromagnetic materials based on a pyrochlore lattice appear to be excellent systems for studying exotic quantum mechanical ground states. It has recently been shown that even ferromagnetically coupled spins can be frustrated on such a lattice, if there is considerable local Ising anisotropy.

Detailed neutron scattering, muon spin relaxation and bulk property measurements taken on the antiferromagnet, Tb2Ti2O7, and the ferromagnet, Ho2Ti2O7, will be presented. Evidence of short-range magnetic correlations, frozen moments and long-range magnetic ordering in different parts of applied field and temperature space will be discussed. Elastic and inelastic neutron scattering studies of Tb2Ti2O7, will be presented. This cooperative paramagnet or spin liquid, with an effective moment of 9.7 µB, has be shown to magnetically order in modest fields and temperatures, however in zero field the system does not order above 15 mK, even with it's large moment. Ho2Ti2O7 is known as a "dipolar spin ice" compound and this will be discussed in some detail.

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