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Induced quadrupolar singlet ground state of praseodymium in a modulated pyrochlore
van Duijn, J.,Kim, K. H.,Hur, N.,Ruiz-Bustos, R.,Adroja, D. T.,Bridges, F.,Daoud-Aladine, A.,Fernandez-Alonso, F.,Wen, J. J.,Kearney, V.,Huang, Q. Z.,Cheong, S.-W.,Perring, T. G.,Broholm, C. American Physical Society 2017 Physical Review B Vol.96 No.9
<P>The complex structure and magnetism of Pr2-xBixRu2O7 was investigated by neutron scattering and extended x-ray absorption fine structure. Pr has an approximate doublet ground state and the first excited state is a singlet. While the B-site (Ru) is well ordered throughout, this is not the case for the A-site (Pr/Bi). A broadened distribution for the Pr-O-2 bond length at low temperature indicates the Pr environment varies from site to site even for x = 0. The environment about the Bi site is highly disordered ostensibly due to the 6s lone pairs on Bi3+. Correspondingly, we find that the non-Kramers doublet ground-state degeneracy, otherwise anticipated for Pr in the pyrochlore structure, is lifted so as to produce a quadrupolar singlet ground statewith a spatially varying energy gap. For x = 0, below TN, the Ru sublattice orders antiferromagnetically, with propagation vector k = (0,0,0) as forY(2)Ru(2)O(7). No ordering associated with the Pr sublattice is observed down to 100 mK. The low-energy magnetic response of Pr2-xBixRu2O7 features a broad spectrum of magnetic excitations associated with inhomogeneous splitting of the Pr quasidoublet ground state. For x = 0 (x = 0.97), the spectrum is temperature dependent (independent). It appears disorder associated with Bi alloying enhances the inhomogeneous Pr crystal-field level splitting so that intersite interactions become irrelevant for x = 0.97. The structural complexity for the A-site may be reflected in the hysteretic uniform magnetization of B-site ruthenium in the Neel phase.</P>
Inhomogeneous Level Splitting inPr2−xBixRu2O7
van Duijn, J.,Kim, K. H.,Hur, N.,Adroja, D.,Adams, M. A.,Huang, Q. Z.,Jaime, M.,Cheong, S.-W.,Broholm, C.,Perring, T. G. American Physical Society 2005 Physical review letters Vol.94 No.17
<P>We report that Bi doping drives Pr 2-x BixRu2O7 from an antiferromagnetic insulator (x = 0) to a metallic paramagnet (x approximately 1) with a broad low T maximum in C/T. Neutron scattering reveals local low energy spin excitations (variant Planck's omega approximately 1 meV) with a spectrum that is unaffected by heating to k(B)T >> variant Planck's omega. We show that a continuous distribution of splittings of the non-Kramers Pr3+ ground-state doublet such as might result from various types of lattice strain can account for all the data.</P>