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We present a combined experimental and theoretical study of the mineral atacamite Cu2Cl(OH)3.Based on ab initio band structure calculations, we derive a magnetic coupling scheme of essentially a S = 1/2 sawtooth chain. Experimentally, we fully characterize the long-range antiferromagnetically ordered state and field-induced behavior, here for H k b axis. Magnetic order is suppressed by magnetic fields of ∼ 20 T, while beginning at 31.5 T we observe a wide magnetization plateau at half of the saturation magnetization, Msat/2. Numerical calculations for the magnetization M(H) of the quantum sawtooth chain reveal a plateau at Msat/2, raising the issue of the understandingof its microscopic nature. Fil: Heinze, L.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemania Fil: Jeschke, H.. Okayama University; Japón. Goethe Universitat Frankfurt; Alemania Fil: Metavitsiadis, A.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemania Fil: Reehuis, M.. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH; Alemania Fil: Feyerherm, R.. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH; Alemania Fil: Hoffmann, J. U.. Helmholtz-Zentrum Berlin für Materialien und Energie GmbH; Alemania Fil: Wolter, A. U. B.. Leibniz Institute For Solid State And Materials Researc; Alemania Fil: Ding, X.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Zapf, V.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Corvalán Moya, Carolina del Huerto. Comisión Nacional de Energía Atómica; Argentina. Los Alamos National High Magnetic Field Laboratory; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Weickert, F.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Jaime, M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Rule, K. C.. Australian Nuclear Science And Technology Organisation; Australia Fil: Menzel, D.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemania Fil: Valenti, R.. Goethe Universitat Frankfurt; Alemania Fil: Brenig, W.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemania Fil: Süllow, S.. Technische Universitat Carolo Wilhelmina Zu Braunschweig.; Alemania

We have carried out a structural and magnetic characterization of Co8Zn8+y Mn4−y−x Fex by means of bulk techniques, powder neutron scattering and Mössbauer spectroscopy. From our data, we derive the main magnetic parameters and carry out a detailed structural characterization.Weobserve that disorder is present in our samples in various forms and that this seems to be generic for this class of materials. However, the disorder appears to have little impact on the character of the magnetic phases, and thus seems to be of no relevance for the skyrmionic phases established for these types of materials.

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The tetragonal compound UPt2Si2 has been characterized as a moderately mass-enhanced system with an antiferromagnetic (AFM) ground state below TN = 32 K. Here, we present an extensive study of the behavior in high magnetic fields.We have performed pulsed field magnetization and static field resistivity measurements on single crystalline samples UPt2Si2. Along the crystallographic a axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 40 T, possibly indicating a first-order transition. Along the crystallographic c axis, in magnetic fields of B ≥ 24 T, we find distinct anomalies in both properties. From our analysis of the data we can distinguish new high-field phases above the AFM ground state. We discuss the emergence of these new phases in the context of Fermi surface effects and the possible occurrence of a Lifshitz or electronic topological transition, this in contrast to previous modelings of UPt2Si2 based on crystal electric field effects.

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 ∼7.6, ∼10.5, and ∼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 J1-J2 spin model, our experimental data are described by various theoretical approaches, yielding values for the exchange interactions J1 ∼ −100 K and J2 ∼ 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 α = J2/|J1| ≈ 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 TN = 2.75(5) K, in agreement with the calculated exchange constants.