arXiv subjects

Paul A. McClarty

Publications and source records attributed to Paul A. McClarty.

22 records · Page 2Linked to original sources

arXiv2011

Order-by-Disorder in the XY Pyrochlore Antiferromagnet Revisited

We investigate the properties of the XY pyrochlore antiferromagnet with local <111> planar anisotropy. We find the ground states and show that the configurational ground state entropy is subextensive. By computing the free energy due to harmonic fluctuations and by carrying out Monte Carlo simulations, we confirm earlier work indicating that the model exhibits thermal order-by-disorder leading to low temperature long-range order consisting of discrete magnetic domains. We compute the spin wave spectrum and show that thermal and quantum fluctuations select the same magnetic structure. Using Monte Carlo simulations, we find that the state selected by thermal fluctuations in this XY pyrochlore antiferromagnet can survive the addition of sufficiently weak nearest-neighbor pseudo-dipolar interactions to the spin Hamiltonian. We discuss our results in relation to the Er2Ti2O7 pyrochlore antiferromagnet.

cond-mat.stat-mech↗

arXiv2011

Rods of Neutron Scattering Intensity in Yb2Ti2O7: Compelling Evidence for Significant Anisotropic Exchange in a Magnetic Pyrochlore Oxide

Paramagnetic correlations in the magnetic material Yb2Ti2O7 have been investigated via neutron scattering, revealing a [111] rod of scattering intensity. Assuming interactions between the Yb^{3+} ions composed of all symmetry-allowed nearest neighbor exchange interactions and long-range dipolar interactions, we construct a model Hamiltonian that allows for an excellent description of the neutron scattering data. Our results provide compelling evidence for significant anisotropic exchange interactions in an insulating magnetic pyrochlore oxide. We also compute the real space correlations leading to the [111] rod of scattering.

cond-mat.str-el↗

arXiv2010

Soft dipolar spin ice physics and the ordered phase of the frustrated Tb2Sn2O7 pyrochlore magnet

From a microscopic model for the pyrochlore antiferromagnet Tb2Sn2O7, including the crystal field Hamiltonian and interactions between the angular momenta, we compute an effective pseudospin-1/2 Hamiltonian Heff$ that incorporates perturbatively in the effective interactions the effect of excited crystal field levels. We obtain the semiclassical ground states of Heff and find a region of parameter space with a two-in/two-out spin ice configuration on each tetrahedron with ordering wavevector q=0 and with spins canted away from the local Ising axes as found in Tb2Sn2O7. This ground state can also be obtained from a dipolar spin ice model in which the Ising constraint is softened. Monte Carlo simulations on the latter model reveal a region of the phase diagram with spin ice-like freezing and another with a transition into Tb2Sn2O7-type long range order. We comment on the differences between Tb2Sn2O7 and the perplexing spin liquid Tb2Ti2O7.

cond-mat.stat-mech↗

arXiv2009

Towards an Effective Spin Hamiltonian of the Pyrochlore Spin Liquid Tb2Ti2O7

Tb2Ti2O7 is a pyrochlore antiferromagnet that has dynamical spins and only short-range correlations even at 50 mK; the lowest temperature explored so far, which is much smaller than the scale set by the Curie-Weiss temperature T_{CW}~14 K. The absence of long-range order in this material is not understood. Recently, virtual crystal field excitations (VCFEs) have been shown to be significant in Tb2Ti2O7. While previous work found that VCFEs-induced renormalization of the nearest neighbor Ising exchange leads to spin ice correlations on a single tetrahedron, their effect on spin correlations has not been fully explored. In this paper, we construct an effective spin-1/2 low-energy theory for Tb2Ti2O7 on the pyrochlore lattice. We determine semiclassical ground states on a lattice that allow us to see how the physics of spin ice is connected to the possible physics of Tb2Ti2O7. We observe a shift in the phase boundaries with respect to those of the dipolar spin ice model as the quantum corrections become more significant. In addition to the familiar classical dipolar spin ice model phases, we see a stabilization of a q = 0 ordered ice phase over a large part of the phase diagram; ferromagnetic correlations being preferred by quantum corrections in spite of an antiferromagnetic nearest neighbor exchange in the microscopic model. Frustration is hence seen to arise from virtual crystal field excitations over and above the effect of dipolar interactions in spin ice in inducing ice-like correlations.

cond-mat.stat-mech↗