Browsing by Author "Kiefer, K"

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    Magnetic frustration in a quantum spin chain: the case of Linarite PbCuSO4(OH)(2)
    (American Physical Society, 2012-03-16) Willenberg, B; Schäpers, M; Rule, KC; Süllow, S; Reehuis, M; Ryll, H; Klemke, B; Kiefer, K; Schottenhamel, W; Büchner, B; Ouladdiaf, B; Uhlarz, M; Beyer, R; Wosnitza, J; Wolter, A U B
    We present a combined neutron diffraction and bulk thermodynamic study of the natural mineral linarite PbCuSO4(OH)(2), this way establishing the nature of the ground-state magnetic order. An incommensurate magnetic ordering with a propagation vector k = (0, 0.186, 1/2) was found below T-N = 2.8 K in a zero magnetic field. The analysis of the neutron diffraction data yields an elliptical helical structure, where one component (0.638 mu(B)) is in the monoclinic ac plane forming an angle with the a axis of 27(2)degrees, while the other component (0.833 mu(B)) points along the b axis. From a detailed thermodynamic study of bulk linarite in magnetic fields up to 12 T, applied along the chain direction, a very rich magnetic phase diagram is established, with multiple field-induced phases, and possibly short-range-order effects occurring in high fields. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. Long-range magnetic order is brought about by interchain coupling 1 order of magnitude smaller than the intrachain coupling. © 2012, American Physical Society.
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    Neutron study of the magnetism in NiCl2•4SC(NH2)2
    (IOP Publishing Ltd., 2013-05-29) Tsyrulin, N; Batista, CD; Zapf, VS; Jaime, M; Hansen, BR; Niedermayer, C; Rule, KC; Habicht, K; Prokes, K; Kiefer, K; Ressouche, E; Paduan, A; Kenzelmann, M
    We study the strongly anisotropic quasi-one-dimensional S = 1 quantum magnet NiCl2 center dot 4SC(NH2)(2) using elastic and inelastic neutron scattering. We demonstrate that a magnetic field splits the excited doublet state and drives the lower doublet state to zero energy at a critical field H-c1. For H-c1 < H < H-c2, where H-c2 indicates the transition to a fully magnetized state, three-dimensional magnetic order is established with the AF moment perpendicular to the magnetic field. We mapped the temperature/magnetic field phase diagram, and we find that the total ordered magnetic moment reaches m(tot) = 2.1 mu(B) at the field mu H-0 = 6 T and is thus close to the saturation value of the fully ordered moment. We study the magnetic spin dynamics in the fully magnetized state for H > H-c2, and we demonstrate the presence of an AF interaction between Ni2+ on the two interpenetrating sublattices. In the antiferromagnetically ordered phase, the spin-waves that develop from the lower-energy doublet are split into two modes. This is most likely the result of the presence of the AF interaction between the interpenetrating lattices.© 2013 IOP Publishing LTD.
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    Thermodynamic properties of the anisotropic frustrated spin-chain compound linarite PbCuSO4(OH)2
    (American Physical Society, 2013-11-15) Schäpers, M; Wolter, AUB; Drechsler, SL; Nishimoto, S; Müller, KH; Abdel-Hafiez, M; Schottenhamel, W; Büchner, B; Richter, J; Ouladdiaf, B; Uhlarz, M; Beyer, R; Skourski, Y; Wosnitza, J; Rule, KC; Ryll, H; Klemke, B; Kiefer, K; Reehuis, M; Willenberg, B; Süllow, S
    We present a comprehensive macroscopic thermodynamic study of the quasi-one-dimensional (1D) s = 1/2 frustrated spin-chain system linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect, magnetostriction, and thermal-expansion measurements were performed to characterize the magnetic phase diagram. In particular, for magnetic fields along the b axis five different magnetic regions have been detected, some of them exhibiting short-range-order effects. The experimental magnetic entropy and magnetization are compared to a theoretical modeling of these quantities using density matrix renormalization group (DMRG) and transfer matrix renormalization group (TMRG) approaches. Within the framework of a purely 1D isotropic model Hamiltonian, only a qualitative agreement between theory and the experimental data can be achieved. Instead, it is demonstrated that a significant symmetric anisotropic exchange of about 10% is necessary to account for the basic experimental observations, including the three-dimensional (3D) saturation field, and which in turn might stabilize a triatic (three-magnon) multipolar phase. © 2013, American Physical Society.