30 research outputs found
Structure and magnetic interactions in the solid solution Ba3-xSrxCr2O8
Solid solutions of the magnetic insulators Ba3Cr2O8 and Sr3Cr2O8
(Ba3-xSrxCr2O8) have been prepared in polycrystalline form for the first time.
Single crys- talline material was obtained using a mirror image floating zone
technique. X-ray diffraction data taken at room temperature indicate that the
space group of Ba3-xSrxCr2O8 remains unchanged for all values of x, while the
cell parameters depend on the chemical composition, as expected. Magnetization
data, measured from 300 K down to 2 K, suggests that the interaction constant
Jd within the Cr5+ dimers varies in a peculiar way as a function of x, starting
at Jd = 25K for x = 0, then first slightly dropping to Jd = 18K for x = 0.75,
before reaching Jd = 62K for x = 3
Definitive Evidence for Order-by-Quantum-Disorder in Er2Ti2O7
Here we establish the systematic existence of a U(1) degeneracy of all
symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice,
at the mean-field level. By extracting the Hamiltonian of Er2Ti2O7 from
inelastic neutron scattering measurements, we then show that the
U(1)-degenerate states of Er2Ti2O7 are its classical ground states, and
unambiguously show that quantum fluctuations break the degeneracy in a way
which is confirmed by experiment. This is the first definitive observation of
order-by-disorder in any material. We provide further verifiable consequences
of this phenomenon, and several additional comparisons between theory and
experiment.Comment: 4.5 pages, 3 figures, 7.5 pages of Supplemental Material, 8
supplemental figure