J. S. Gardner

Two-dimensional kagome correlations and field induced order in the ferromagnetic XY pyrochlore Yb2Ti2O7.

Neutron scattering measurements show the ferromagnetic XY pyrochlore Yb2Ti2O7 to display strong quasi-two-dimensional (2D) spin correlations at low temperature, which give way to long range order (LRO) under the application of modest magnetic fields. Rods of scattering along 111 directions due to these 2D spin correlations imply a magnetic decomposition of the cubic pyrochlore system into decoupled kagome planes. A magnetic field of approximately 0.5 T applied along the [110] direction induces a transition to a 3D LRO state characterized by long-lived, dispersive spin waves. Our measurements map out a complex low temperature-field phase diagram for this exotic pyrochlore magnet.

Revisiting static and dynamic spin-ice correlations in Ho₂Ti₂O₇ with neutron scattering

J.P. Clancy, J.P.C. Ruff, S.R. Dunsiger, Y. Zhao, H.A. Dabkowska, J.S. Gardner, 3 Y. Qiu, 4 J.R.D. Copley, T. Jenkins, and B.D. Gaulin 5 Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1 NIST Center for Neutron Research, NIST, Gaithersburg, Maryland 20899-8102, USA Indiana University, 2401 Milo B. Sampson Lane, Bloomington, Indiana 47408, USA Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA Canadian Institute for Advanced Research, 180 Dundas Street W., Toronto, Ontario, Canada M5G 1Z8

High pressure route to generate magnetic monopole dimers in spin ice

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas, like monopole dimerization, critical phase separation, or charge ordering. However, all known spin ices have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, where none of these interesting phenomena occur. Here we use high-pressure synthesis to create a new monopole host, Dy2Ge2O7, with a radically altered chemical potential that stabilizes a large fraction of monopole dimers. The system is found to be ideally described by the classic Debye–Huckel–Bjerrum theory of charge correlations. We thus show how to tune the monopole chemical potential in spin ice and how to access the diverse collective properties of magnetic monopoles.

Field-Induced Order and Spin Waves in the Pyrochlore Antiferromagnet Tb~2Ti~2O~7

High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of a magnetic field applied along [110]. In zero field at T = 0.4 K, Tb(2)Ti(2)0(7) is a highly correlated cooperative paramagnet with disordered spins residing on a pyrochlore lattice of corner-sharing tetrahedra. Application of a small field condenses much of the magnetic diffuse scattering, characteristic of the disordered spins, into a new Bragg peak characteristic of a polarized paramagnet. At higher fields, a magnetically ordered phase is induced, which supports spin wave excitations indicative of continuous, rather than Ising-like, spin degrees of freedom.

Statics and dynamics of the highly correlated spin ice Ho2Ge2O7

The pyrochlore Ho

Unconventional spin glass behavior in the cubic pyrochlore Mn2Sb2O7

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Magnetic order in the double pyrochlore Tb2Ru2O7

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Lack of evidence for a singlet crystal-field ground state in the magnetic pyrochlore Tb 2 Ti 2 O 7

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The origin of persistent spin dynamics and residual entropy in the stuffed spin ice Ho2.3Ti1.7O7−δ

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Frustrated spin correlations in diluted spin ice Ho2−xLaxTi2O7

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