Browsing by Author "Schäpers, M"

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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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    Magnetic properties and exchange integrals of the frustrated chain cuprate linarite PbCuSO4(OH)2
    (American Physical Society, 2012-01-05) Wolter, AUB; Lipps, F; Schäpers, M; Drechsler, SL; Nishimoto, S; Vogel, R; Kataev, V; Büchner, B; Rosner, H; Schmitt, M; Uhlarz, M; Skourski, Y; Wosnitza, J; Süllow, S; Rule, KC
    We present a detailed study in the paramagnetic regime of the frustrated s = 1/2 spin-compound linarite PbCuSO4(OH)(2) with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions. Our data reveal highly anisotropic values for the saturation field along the crystallographic main directions, with similar to 7.6, similar to 10.5, and similar to 8.5 T for the a, b, and c axes, respectively. In the paramagnetic regime, this behavior is explained mainly by the anisotropy of the g factor, but leaving room for an easy-axis exchange anisotropy. Within the isotropic J(1)-J(2) spin model, our experimental data are described by various theoretical approaches, yielding values for the exchange interactions J(1) similar to -100 K and J(2) similar to 36 K. These main intrachain exchange integrals are significantly larger as compared to the values derived in two previous studies in the literature and shift the frustration ratio alpha = J(2)/vertical bar J(1)vertical bar approximate to 0.36 of linarite closer to the one-dimensional critical point at 0.25. Electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements further prove that the static susceptibility is dominated by the intrinsic spin susceptibility. The Knight shift as well as the broadening of the linewidth in ESR and NMR at elevated temperatures indicate a highly frustrated system with the onset of magnetic correlations far above the magnetic ordering temperature T-N = 2.75(5) K, in agreement with the calculated exchange constants. © 2012, American Physical Society.
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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.