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Collaborative Study of Geometrically Frustrated Magnetic Materials: New Materials and New Physics DMR-0353610 Peter Schiffer, Penn State Univ. and Robert Cava, Princeton Univ.

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  1. Collaborative Study of Geometrically Frustrated Magnetic Materials: New Materials and New Physics DMR-0353610Peter Schiffer, Penn State Univ. and Robert Cava, Princeton Univ. Our research is into the properties of “frustrated” magnetic materials. In such materials, the atoms have magnetic moments, and are analogous to microscopic bar magnets. These magnetic moments interact with each other, trying to orient in particular ways relative to their neighbors. They are frustrated in the sense that these interactions compete with each other, so that no set of orientations of all the magnetic moments will satisfy all of these interactions. Understanding the peculiar behavior resulting from this frustration can give insight into a range of similarly frustrated systems, such as neural networks. a b c The structure of the frustrated pyrochlore and stuffed pyrochlore titanates R2M2O7 and R2(M2-xRx)O7-x/2 as exemplified by the spin ice materialHo2Ti2O7 and Ho2(Ti2‑xHox)O7-x/2. a. The magnetic sublattice of Ho ions in Ho2Ti2O7, which is composed of corner-sharing tetrahedra. b. The magnetic sublattice of Ho ions in Ho2Ti2O7, with the equivalent interpenetrating Ti sublattice of corner-sharing tetrahedra also shown. c. The combination of the two lattices of corner-sharing tetrahedra form a lattice of side-sharing tetraheda (equivalent to the fcc lattice). This combined lattice is randomly populated with Ho and Ti ions for x = 0.67. Despite the change in structure and connectivity of the magnetic lattice, the “stuffed” material retains the same ground state entropy as the spin ice material, i.e., it is disordered even at zero temperature. G. Lau et al., Nature Physics 2006

  2. Penn State MRSEC and REU program DMR-0213623support for undergraduate research William McConville was named a finalist for the Vanderbilt Prize for Undergraduate Research, a national award which recognizes original research conducted by undergraduate students. He was chosen for his contributions to research involving the study of geometrical magnetic frustration within arrays of lithographically fabricated nanoscale ferromagnetic islands. The article describing the work in which he participated, and an image he created, were featured on the cover of the January 19, 2006 issue of the journal Nature. This magnetic-force microscope image (created by undergraduate, William McConville) shows the magnetic moments of artificial spin ice. The peaks and valleys show the orientations of the magnetic moments. A similar image appeared on the cover of the issue of the journal Nature in which this research was published. R. Wang et al. Nature 2006

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