Spin Correlations inHo2Ti2O7: A Dipolar Spin Ice System

Abstract

The pyrochlore material Ho2Ti2O7 has been suggested to show "spin ice" behaviour. We present neutron scattering and specific heat results that establish unambiguously that Ho2Ti2O7 exhibits spin ice correlations at low temperature. Diffuse magnetic neutron scattering from Ho2Ti2O7 is found to be quite well described by a nearest neighbour spin ice model and very accurately described by a dipolar spin ice model. The heat capacity is well accounted for by the sum of a dipolar spin ice contribution and an expected nuclear spin contribution, known to exist in other Ho 3+ salts. These results settle the question of the nature of the low temperature spin correlations in Ho2Ti2O7 for which contradictory claims have been made.

Microscopic aspects of magnetic lattice demagnetizing factors

“…We illustrate this explicitly by a numerical MC simulation of the so-called dipolar spin ice model, which has been found to reproduce a number of properties of the Dy 2 Ti 2 O 7 and Ho 2 Ti 2 O 7 dipolar spin ice materials [33,34,55,56]. The Hamiltonian for this model consists of the dipolar term defined in Eq.…”

Dirty spin ice: The effect of dilution on spin freezing inDy2Ti2OSnyder1, Slusky2, Cava3 et al. 2002Phys. Rev. B484330View full textAdd to dashboardCite

“…The spin ice state has been demonstrated experimentally through neutron scattering studies [5,12,20] and also through measurements of the magnetic specific heat, which yield a measured ground state entropy in good agreement with the theoretical prediction for the "ice rules" (first codified by Pauling) and experimental results for ice [7,17,19]. While the spin entropy only freezes out below T ~ 3 K in Dy 2 Ti 2 O 7 , magnetic susceptibility studies show a strongly frequency dependent cooperative spin-freezing at T 3 16 K [8,9], and then a sharp drop at T ~ 2 K [21].…”

“…In spin ice materials, the magnetic rare-earth ions are situated on a lattice of corner-sharing tetrahedra, and their spins are constrained by crystal field interactions to point either directly toward or directly away from the centers of the tetrahedra as shown in figure 1b. To minimize the dipole and ferromagnetic exchange interactions, the spins on each tetrahedron must be oriented such that two spins point inward and two point outward in exact analogy to the protons in ice.The spin ice state has been demonstrated experimentally through neutron scattering studies [5,12,20] and also through measurements of the magnetic specific heat, which yield a measured ground state entropy in good agreement with the theoretical prediction for the "ice rules" (first codified by Pauling) and experimental results for ice [7,17,19]. While the spin entropy only freezes out below T ~ 3 K in Dy 2 Ti 2 O 7 , magnetic susceptibility studies show a strongly frequency dependent cooperative spin-freezing at T 3 16 K [8,9], and then a sharp drop at T ~ 2 K [21].…”

Quantum fluctuations in spin-ice-like Pr2Zr2O7

“…Sharp pinch point features near (111) and particularly (002), bear evidence of a divergence-free two-in two-out spin configuration on each tetrahedron 9,25,29,30 . Indeed, the elastic Q-map resembles a classical Monte Carlo simulation for an exchange-only model 9,29 , which indicates dominant ferromagnetic superexchange interactions in Pr 2 Zr 2 O 7 . Y W is, however, negative and this suggestsconsistent with recent theoretical predictions 31,32 -the exchange Hamiltonian includes antiferromagnetic transverse terms that induce quantum dynamics.…”