Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffedYb2Ti2O7

Abstract

Time-of-flight neutron spectroscopy has been used to determine the crystalline electric field (CEF) Hamiltonian, eigenvalues and eigenvectors appropriate to the J = 7/2 Yb 3+ ion in the candidate quantum spin ice pyrochlore magnet Yb2Ti2O7. The precise ground state (GS) of this exotic, geometrically-frustrated magnet is known to be sensitive to weak disorder associated with the growth of single crystals from the melt. Such materials display weak "stuffing" wherein a small proportion, ≈ 2%, of the non-magnetic Ti 4+ sites are occupied by excess Yb 3+ . We have carried out neutron spectroscopic measurements on a stoichiometric powder sample of Yb2Ti2O7, as well as a crushed single crystal with weak stuffing and an approximate composition of Yb2+xTi2−xO7+y with x = 0.046. All samples display three CEF transitions out of the GS, and the GS doublet itself is identified as primarily composed of mJ = ±1/2, as expected. However,"stuffing" at low temperatures in Yb2+xTi2−xO7+y induces a similar finite CEF lifetime as is induced in stoichiometric Yb2Ti2O7 by elevated temperature. We conclude that an extended strain field exists about each local "stuffed" site, which produces a distribution of random CEF environments in the lightly stuffed Yb2+xTi2−xO7+y, in addition to producing a small fraction of Yb-ions in defective environments with grossly different CEF eigenvalues and eigenvectors.

Effect of chemical pressure on the crystal electric field states of erbium pyrochlore magnets

“…7 where it is compared with the measured schemes from Refs. [36,38,39]. The CEF schemes obtained from this procedure have good qualitative agreement with the experimental data, but are quantitatively inaccurate, which should not be surprising for several reasons.…”

Gapped and gapless short-range-ordered magnetic states with(12,12,12)wave vectors in the pyrochlore magnet

“…Such stuffed, B-site, Tb ions would experience different crystal field effects from the A-site Tb ions, and these may act as impurities with a different aspherical f −electron charge distribution that are effective in frustrating higher-than-dipole order. Such a scenario of very different crystal field eigenfunctions for rare earth ions on A and B sublattices has recently been discussed for Yb 2+x Ti 2−x O 7+δ [30]. Additionally, there is the question of why the ordered states of Tb 2+x Ti 2−x O 7+δ are not centered at x = 0; indeed T C appears to be maximal at x ∼ +0.005.…”

XY antiferromagnetic ground state in the effectiveS=12pyrochloreYb2Ge2O7Hallas1, Gaudet2, Wilson3 et al. 2016Phys. Rev. BSelf Cite383350View full textAdd to dashboardCite

“…The crystal electric field states for Yb 2 Ti 2 O 7 are well understood [7][8][9], while those corresponding to Er 2 Ti 2 O 7 are less well-determined [10,11] [8,12,13]. These two materials have also both been found to order into a canted ferromagnetic state at low temperatures [13][14][15][16].…”