L. R. Yaraskavitch

Publications (6)0 Total impact

• Article: Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique

  K. A. Ross, Th. Proffen, H. A. Dabkowska, J. A. Quilliam, L. R. Yaraskavitch, J. B. Kycia, B. D. Gaulin
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  ABSTRACT: Recent neutron scattering and specific heat studies on the pyrochlore Yb2Ti2O7 have revealed variations in its magnetic behavior below 265mK. In the best samples, a sharp anomaly in the specific heat is observed at T=265mK. Other samples, especially single crystals, have broad features in the specific heat which vary in sharpness and temperature depending on the sample, indicating that the magnetic ground state may be qualitatively different in such samples. We performed detailed comparisons of the chemical structure of a pulverised single crystal of Yb2Ti2O7, grown by the floating zone technique, to a sintered powder sample of Yb2Ti2O7. Rietveld refinements of neutron powder diffraction data on these samples reveal that the crushed single crystal is best described as a "stuffed" pyrochlore, Yb2(Ti(2-x)Yb(x))O7-(x/2) with x = 0.046(4), despite perfectly stoichiometric starting material. Substituting magnetic Yb3+ on the non-magnetic Ti4+ sublattice would introduce random exchange bonds and local lattice deformations. These are expected to be the mechanism leading to of the variation of the delicate magnetic ground state of Yb2Ti2O7. Determination of the cubic cell length, a, could be useful as a method for characterizing the stoichiometry of non- pulverised single crystals at room temperature.
  08/2012;
• Article: Dimensional evolution of spin correlations in the magnetic pyrochlore Yb_ {2} Ti_ {2} O_ {7}

  K. A. Ross, L. R. Yaraskavitch, M. Laver, J. S. Gardner, J. A. Quilliam, S. Meng, J. B. Kycia, D. K. Singh, Th. Proffen, H. A. Dabkowska, B. D. Gaulin
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  ABSTRACT: The pyrochlore material Yb2Ti2O7 displays unexpected quasi-two-dimensional (2D) magnetic correlations within a cubic lattice environment at low temperatures, before entering an exotic disordered ground state below T=265 mK. We report neutron scattering measurements of the thermal evolution of the 2D spin correlations in space and time. Short-range three-dimensional (3D) spin correlations develop below 400 mK, accompanied by a suppression in the quasielastic (QE) scattering below ∼0.2 meV. These show a slowly fluctuating ground state with spins correlated over short distances within a kagome-triangular-kagome (KTK) stack along [111], which evolves to isolated kagome spin stars at higher temperatures. Furthermore, low-temperature specific heat results indicate a sample dependence to the putative transition temperature that is bounded by 265 mK, which we discuss in the context of recent mean field theoretical analysis.
  Phys. Rev. B. 11/2011; 84(17).
• Source

  Available from: ArXiv

  Article: Dimensional Evolution of Spin Correlations in the Magnetic Pyrochlore Yb2Ti2O7

  K. A. Ross, L. R. Yaraskavitch, M. Laver, J. S. Gardner, J. A. Quilliam, S. Meng, J. B. Kycia, D. K. Singh, H. A. Dabkowska, B. D. Gaulin
  [show abstract] [hide abstract]
  ABSTRACT: The pyrochlore material Yb2Ti2O7 displays unexpected quasi-two-dimensional (2D) magnetic correlations within a cubic lattice environment at low temperatures, before entering an exotic disordered ground state below T=265mK. We report neutron scattering measurements of the thermal evolution of the 2D spin correlations in space and time. Short range three dimensional (3D) spin correlations develop below 400 mK, accompanied by a suppression in the quasi-elastic (QE) scattering below ~ 0.2 meV. These show a slowly fluctuating ground state with spins correlated over short distances within a kagome-triangular-kagome (KTK) stack along [111], which evolves to isolated kagome spin-stars at higher temperatures. Furthermore, low-temperature specific heat results indicate a sample dependence to the putative transition temperature that is bounded by 265mK, which we discuss in the context of recent mean field theoretical analysis.
  07/2011;
• Source

  Available from: ArXiv

  Article: Dynamics of the Magnetic Susceptibility Deep in the Coulomb Phase of the Dipolar Spin Ice Material Ho2Ti2O7

  J. A. Quilliam, L. R. Yaraskavitch, H. A. Dabkowska, B. D. Gaulin, J. B. Kycia
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  ABSTRACT: Low temperature measurements of the ac magnetic susceptibility along the [110] direction of a single crystal of the dipolar spin ice material Ho2Ti2O7, in zero static field, are presented. While behavior that is qualitatively consistent with previous work on Ho2Ti2O7 and the related material Dy2Ti2O7 is observed, this work extends measurements to appreciably lower temperatures and frequencies. In the freezing regime, below 1 K, the dynamics are found to be temperature activated, thus well described by an Arrhenius law with an activation energy close to 6J_eff, a result that is not easily explained with the current model of magnetic monopole excitations in dipolar spin ice. The form and temperature dependence of the ac susceptibility spectra are found to be nontrivial and distinct from standard glassy relaxation. Particular attention has been paid to correcting for the demagnetization effect, which is quite significant in these materials and has important, even qualitative, effects on the susceptibility spectra.
  02/2011;
• Article: Spin dynamics in the frozen state of the dipolar spin ice material Dy_ {2} Ti_ {2} O_ {7}

  L. R. Yaraskavitch, H. M. Revell, S. Meng, K. A. Ross, H. M. L. Noad, H. A. Dabkowska, B. D. Gaulin, J. B. Kycia
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  ABSTRACT: Low-temperature magnetic ac susceptibility measurements of single-crystal dipolar spin ice Dy2Ti2O7 are presented. The relaxation is found to exhibit thermally activated Arrhenius behavior with an activation energy of 9.79 K (∼9Jeff), which is not consistent with a simple scaling of 6Jeff, as previously found for Ho2Ti2O7. There are distinct quantifiable differences between Dy2Ti2O7 and Ho2Ti2O7 absorption spectra. The measured dynamics does not agree with simulations based on current magnetic monopole theory nor thermal relaxation measurements, but instead freezes out at a faster rate.
  Phys. Rev. B. 85(2).
• Article: Dynamics of the magnetic susceptibility deep in the Coulomb phase of the dipolar spin ice material Ho_ {2} Ti_ {2} O_ {7}

  J. A. Quilliam, L. R. Yaraskavitch, H. A. Dabkowska, B. D. Gaulin, J. B. Kycia
  [show abstract] [hide abstract]
  ABSTRACT: Low-temperature measurements of the ac magnetic susceptibility along the [110] direction of a single crystal of the dipolar spin ice material Ho2Ti2O7, in zero static field, are presented. While behavior that is qualitatively consistent with previous work on Ho2Ti2O7 and the related material Dy2Ti2O7 is observed, this work extends measurements to appreciably lower temperatures and frequencies. In the freezing regime, below 1 K, the dynamics are found to be temperature activated, thus well described by an Arrhenius law with an activation energy close to 6Jeff, a result that is not easily explained with the current model of magnetic monopole excitations in dipolar spin ice. The form and temperature dependence of the ac susceptibility spectra are found to be nontrivial and distinct from standard glassy relaxation. Particular attention has been paid to correcting for the demagnetization effect, which is quite significant in these materials and has important, even qualitative, effects on the susceptibility spectra.
  Phys. Rev. B. 83(9).