Magnetic correlations in spin ice Ho2-xYxTi2O7 as revealed by neutron
  polarization analysis

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Abstract

We present single-crystal neutron-diffuse-scattering measurements with polarization analysis on the spin ice Ho2-xYxTi2O7 (x = 0, 0.3, and 1). At 2 K, the spin flip scattering patterns are typical of a nearest-neighbor spin ice and the effects of Y doping are seen in the width of the pinch points. At low-T, the spin flip patterns are characteristic of a dipolar spin ice and are unaffected by Y doping. In the non-spin flip channel, we observe the signature of strong antiferromagnetic correlations at the same T as the dipolar spin ice correlations appear in the spin flip channel. These experimental observations have been well reproduced by our Monte Carlo simulations.

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Magnetic Pyrochlore Oxides

, , (2010)

Within the past 20 years or so, there has occurred an explosion of interest in the magnetic behavior of pyrochlore oxides of the type \(A_{2}^{3+}\)\(B_{2}^{4+}\(O\)_{7}\( where \)A\( is a rare-earth ion and \)B\( is usually a transition metal. Both the \)A\( and \)B\) sites form a network of corner-sharing tetrahedra which is the quintessential framework for a geometrically frustrated magnet. In these systems the natural tendency to form long range ordered ground states in accord with the Third Law is frustrated, resulting in some novel short range ordered alternatives such as spin glasses, spin ices and spin liquids and much new physics. This article attempts to review the myriad of properties found in pyrochlore oxides, mainly from a materials perspective, but with an appropriate theoretical context.

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Magnetic and Thermodynamic Properties of the Collective Paramagnet-Spin Liquid Pyrochlore Tb2Ti2O7

N. Raju, B. C. den Hertog, M. Faucher … (2000)

In a recent letter [Phys. Rev. Lett. {\bf 82}, 1012 (1999)] it was found that the Tb\(^{3+}\) magnetic moments in the Tb\(_2\)Ti\(_2\)O\(_7\) pyrochlore lattice of corner-sharing tetrahedra remain in a {\it collective paramagnetic} state down to 70mK. In this paper we present results from d.c. magnetic susceptibility, specific heat data, inelastic neutron scattering measurements, and crystal field calculations that strongly suggest that (1) the Tb\(^{3+}\) ions in Tb\(_2\)Ti\(_2\)O\(_7\) possess a moment of approximatively 5\(\mu_{\rm B}\), and (2) the ground state \(g-\)tensor is extremely anisotropic below a temperature of \(O(10^0)\)K, with Ising-like Tb\(^{3+}\) magnetic moments confined to point along a local cubic \( \) diagonal (e.g. towards the middle of the tetrahedron). Such a very large easy-axis Ising like anisotropy along a \( \) direction dramatically reduces the frustration otherwise present in a Heisenberg pyrochlore antiferromagnet. The results presented herein underpin the conceptual difficulty in understanding the microscopic mechanism(s) responsible for Tb\(_2\)Ti\(_2\)O\(_7\) failing to develop long-range order at a temperature of the order of the paramagnetic Curie-Weiss temperature \(\theta_{\rm CW} \approx -10^1\)K. We suggest that dipolar interactions and extra perturbative exchange coupling(s)beyond nearest-neighbors may be responsible for the lack of ordering of Tb\(_2\)Ti\(_2\)O\(_7\).