Browsing by Author "Peets, DC"
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- Item3d-electron Heisenberg pyrochlore Mn2Sb2O7(American Physical Society, 2016-11-21) Peets, DC; Sim, H; Avdeev, M; Park, JGIn frustrated magnetic systems, geometric constraints or the competition among interactions introduce extre-mely high degeneracy and prevent the system from readily selecting a low-temperature ground state. The most frustrated known spin arrangement is on the pyrochlore lattice, but nearly all magnetic pyrochlores have unquenched orbital angular momenta, constraining the spin directions through spin-orbit coupling. Pyrochlore Mn2Sb2O7 is an extremely rare Heisenberg pyrochlore system with directionally unconstrained spins and low chemical disorder. We show that it undergoes a spin-glass transition at 5.5 K, which is suppressed by disorder arising from Mn vacancies, indicating this ground state to be a direct consequence of the spins' interactions. The striking similarities to 3d transition-metal pyrochlores with unquenched angular momenta suggests that the low spin-orbit coupling in the 3d block makes Heisenberg pyrochlores far more accessible than previously imagined. ©2016 American Physical Society
- ItemCompeting exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7(Americal Physical Society, 2014-10-03) Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, BWe report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr 3 Fe 2 O 7 , which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe 4+ moments adopt incommensurate spiral order below T N =115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr 3 Fe 2 O 7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals. © 2014, American Physical Society.
- ItemCrystal growth, structure, and noninteracting quantum spins in cyanochroite, K2Cu(SO4)2·6H2O(American Chemical Society, 2022-02-15) Peets, DC; Avdeev, M; Rahn, MC; Pabst, F; Granovsky, S; Stötzer, M; Inosov, DSThe rare mineral cyanochroite, K2Cu(SO4)2·6H2O, features isolated Cu2+ ions in distorted octahedral coordination, linked via a hydrogen-bond network. We have grown single crystals of cyanochroite as large as ∼0.5 cm3 and investigated structural and magnetic aspects of this material. The positions of hydrogen atoms deviate significantly from those reported previously based on X-ray diffraction data, whereas the magnetic response is fully consistent with free Cu2+ spins. The structure is not changed by deuteration. Density functional theory calculations support our refined hydrogen positions. © 2022 The Authors. CC-BY 4.0
- ItemMagnetic and electronic properties of single-crystalline BaCoSO(American Physical Society, 2019-11-21) Song, YH; Liu, XS; Wu, D; Yao, Q; Wen, CHP; Avdeev, M; Peng, R; Xu, HC; Miao, J; Lou, X; Fang, YF; Pan, BL; Wang, NL; Peets, DC; Feng, DGDoped BaCoSO was recently predicted to be a high-temperature superconductor in a new class based on Co and Ni. Using a Co-S self-flux method, we synthesized single crystals of the antiferromagnetic insulator BaCoSO. Our magnetic and specific heat measurements and neutron diffraction provide details of its magnetic anisotropy and order. Its band gap was determined to be about 1.3 eV by our measurements of its photoemission spectrum and infrared optical conductivity. Our results can pave the way to exploring the predicted superconductivity in this Co-based material. ©2019 American Physical Society
- ItemMagnetic phase diagram of Sr3Fe2O7-delta(American Physical Society, 2013-06-10) Peets, DC; Kim, JH; Dosanjh, P; Reehuis, M; Maljuk, A; Aliouane, N; Ulrich, C; Keimer, BMagnetometry, electrical transport, and neutron scattering measurements were performed on single crystals of the Fe4+-containing perovskite-related phase Sr3Fe2O7−δ as a function of oxygen content. Although both the crystal structure and electron configuration of this compound are closely similar to those of well-studied ruthenates and manganates, it exhibits very different physical properties. The fully oxygenated compound (δ=0) exhibits a charge-disproportionation transition at TD=340 K, and an antiferromagnetic transition at TN=115 K. For temperatures T≤TD, the material is a small-gap insulator; the antiferromagnetic order is incommensurate, which implies competing exchange interactions between the Fe4+ moments. The fully deoxygenated compound (δ=1) is highly insulating, and its Fe3+ moments exhibit commensurate antiferromagnetic order below TN∼600 K. Compounds with intermediate δ exhibit different order with lower TN, likely as a consequence of frustrated exchange interactions between Fe3+ and Fe4+ sublattices. A previous proposal that the magnetic transition temperature reaches zero is not supported. © 2013, American Physical Society.
- ItemMagnetic transitions in the chiral armchair-kagome system Mn2Sb2O7(American Physical Society, 2017-01-20) Peets, DC; Sim, H; Choi, S; Avdeev, M; Lee, S; Kim, SJ; Kang, H; Ahn, D; Park, JGThe competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. Mn2Sb2O7 forms in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. Mn2Sb2O7 exhibits two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the P3121 space group, Mn2Sb2O7 actually crystallizes in P2, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional “armchair-kagome” lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems. ©2017 American Physical Society
- ItemOptimizing the preparation of monoclinic and pyrochlore Mn2Sb2O7(IOP Publishing, 2017-04-06) Peets, DC; Sim, H; Avdeev, MTwo polymorphs of Mn2Sb2O7 have been reported, in the pyrochlore structure and in a chiral, monoclinic structure. In both cases, magnetization data have shown prominent features attributable to a ferrimagnetic impurity. Accessing the intrinsic physical properties of both materials thus requires first making them phase pure. We describe our efforts to optimize the preparation of both polymorphs and how we concluded this was necessary, in hopes that future work will be aided by detailed knowledge of this process. Published under licence by IOP Publishing Ltd. Creative Commons Attribution 3.0 licence.
- ItemPhysical properties of noncentrosymmetric tungsten and molybdenum aluminides(American Physical Society, 2018-10-16) Peets, DC; Ying, TP; Shen, XP; Yu, YJ; Avdeev, M; Li, SY; Feng, DLA lack of spatial inversion symmetry gives rise to a variety of unconventional physics, from noncollinear order and Skyrmion lattice phases in magnetic materials to topologically protected surface states in certain band insulators to mixed-parity pairing states in superconductors. The search for exotic physics in such materials is largely limited by a lack of candidate materials and often by difficulty in obtaining crystals. Here, we report the single-crystal growth and physical properties of the noncentrosymmetric tungsten aluminide cage compounds Al4W and Al5W, alongside related molybdenum aluminides in which spin-orbit coupling should be significantly weaker. All compounds are nonmagnetic metals. Their high conductivities suggest the opportunity to find superconductivity at lower temperatures, while the limits we can place on their transition temperatures suggest that any superconductivity may be expected to exhibit significant parity mixing. ©2018 American Physical Society
- ItemProperties of spin-1/2 triangular-lattice antiferromagnets CuY2Ge2O8 and CuLa2Ge2O8(American Physical Society, 2017-04-05) Cho, H; Kratochvílová, M; Sim, H; Choi, KY; Kim, CH; Paulsen, C; Avdeev, M; Peets, DC; Jo, Y; Lee, S; Noda, Y; Lawler, MJ; Park, JGWe found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg≅2eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering. ©2017 American Physical Society
- ItemPublisher's Note: 3d-electron Heisenberg pyrochlore Mn2Sb2O7 [Phys. Rev. B 94, 174431 (2016)](American Physical Society, 2017-03-21) Peets, DC; Sim, H; Avdeev, M; Park, JGThis paper was published online on 21 November 2016 with a typographical error on page 2. On page 2, the fourth line of the left-hand column should read as “prepared from SbCl5 (Alfa Aesar, 99.997%) and deionized . . . ” The paper has been corrected as of 10 March 2017. The text is incorrect in the printed version of the journal.