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Multiferroicity in the generic easy-plane triangular lattice antiferromagnet RbFe(MoO4)2
White, J. S.,Niedermayer, Ch.,Gasparovic, G.,Broholm, C.,Park, J. M. S.,Shapiro, A. Ya.,Demianets, L. A.,Kenzelmann, M. American Physical Society 2013 Physical review. B, Condensed matter and materials Vol.88 No.6
Spin-Lattice Order in FrustratedZnCr2O4
Ji, S.,Lee, S.-H.,Broholm, C.,Koo, T. Y.,Ratcliff, W.,Cheong, S.-W.,Zschack, P. American Physical Society 2009 Physical Review Letters Vol.103 No.3
<P>Using synchrotron x-ray and neutron diffraction, we disentangle spin-lattice order in highly frustrated ZnCr2O4 where magnetic chromium ions occupy the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of antialigning spins surrounding the triangular faces of tetrahedra is resolved by establishing weak interactions on each triangle through an intricate lattice distortion. However, the resulting spin order is not simply a Néel state on strong bonds, but rather a complex coplanar spin structure, indicating that antisymmetric and/or further neighbor exchange interactions also play a role as ZnCr2O4 resolves conflicting magnetic interactions.</P>
Crystal distortions in geometrically frustrated ACr<sub>2</sub>O<sub>4</sub> (A = Zn,Cd)
Lee, S-H,Gasparovic, G,Broholm, C,Matsuda, M,Chung, J-H,Kim, Y J,Ueda, H,Xu, G,Zschack, P,Kakurai, K,Takagi, H,Ratcliff, W,Kim, T H,Cheong, S-W IOP Pub 2007 Journal of Physics, Condensed Matter Vol.19 No.14
<P>In this paper, we discuss neutron and synchrotron x-ray diffraction data obtained from single crystals of ACr<SUB>2</SUB>O<SUB>4</SUB> (A = Zn, Cd). The Cr spinels undergo three-dimensional spin-Peierls transitions at low temperatures that involve cubic-to-tetragonal lattice distortions and magnetic long-range ordering. Our results show that the magnetic structures selected by these systems are closely related to the lattice distortions that are undertaken. </P>
Lee, Nara,Choi, Kyunghoon,Uthuppu, Basil,Jakobsen, Mogens H.,Hwang, Yuhoon,Broholm, Mette M.,Lee, Woojin Techno-Press 2014 Advances in environmental research Vol.3 No.2
This study aimed to synthesize dispersed and reactive nanoscale zero-valent iron (nZVI) with poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA), nontoxic and biodegradable stabilizer. The nZVI used for the experiments was prepared by reduction of ferric solution in the presence of PVP/VA with specific weight ratios to iron contents. Colloidal stability was investigated based on the rate of sedimentation, hydrodynamic radius and zeta potential measurement. The characteristic time, which demonstrated dispersivity of particles resisting aggregation, increased from 21.2 min (bare nZVI) to 97.8 min with increasing amount of PVP/VA (the ratios of 2). For the most stable nZVI coated by PVP/VA, its reactivity was examined by nitrate reduction in a closed batch system. The pseudo-first-order kinetic rate constants for the nitrate reduction by the nanoparticles with PVP/VA ratios of 0 and 2 were 0.1633 and $0.1395min^{-1}$ respectively. A nitrogen mass balance, established by quantitative analysis of aqueous nitrogen species, showed that the addition of PVP/VA to nZVI can change the reduction capacity of the nanoparticles.
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>
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>