Magnetic Correlation of Spin Ice Systems(Current Topic)

Abstract

Magnetic moments of R³+ ions of R₂Ti₂O₇ (R = Ho, Dy) with large Ising anisotropy providethe problem of the geometrical frustration which is (almost) equivalent to that of solid H₂O. To investigate what kind of magnetic state is realized in these systems at low temperature, we have carried out neutron diffraction experiments on a single crystal of Ho₂Ti₂O₇. The observedcorrelation pattern can be reproduced by the molecular field treatment and the Monte-Carlo simulation, where the dipolar interaction plays an important role. Although the degeneracy is, strictly speaking, mostly lifted due to theinteraction, the system does not exhibit themagnetic ordering. Instead, with decreasing temperature, before reaching the long range ordered state, it gradually goes into the glassy state, as a result of the coexistence of many spin clusters which have short range magnetic order with different but almost degenerated energies.