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The Hall effect of the disordered and frustrated magnetic alloys Au-Fe 8 at% and Au-Fe 18 at% was studied in applied magnetic fields up to 14 T. The measurements were carried out in fixed temperatu...

Nature photonics 14(6), 391 - 397 (2020). doi:10.1038/s41566-020-0607-z, The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created., Published by Nature Publ. Group, London [u.a.]

The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split-pair magnet. A helium-3 refrigerator is available that can be fitted inside the magnet's variable-temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He-3 insert are presented. By measuring the tetragonal-to-orthorhombic phase transition occurring at 2.1 K in the Jahn–Teller compound TmVO4, it is found that the photon flux at P09 must be attenuated down to 1.5 × 109 photons s−1for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X-ray magnetic scattering signal at the TmLIIIabsorption edge associated with the spin-density wave in TmNi2B2C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub-Kelvin temperatures to be carried out.

An orthorhombic DyMnO 3 single crystal has been studied in magnetic fields up to 14 T and between 3 Kand room temperature. The field dependent ordering temperature of Dy moments is deduced. Theparamagnetic Curie Weiss behavior is related mainly to the Dy 3þ sublattice whereas the Mn sublatticecontribution plays a secondary role. DC magnetization measurements show marked anisotropicfeatures, related to the anisotropic structure of a cubic system stretched along a body diagonal, witha magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin floptransition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome bymagnetic fields up to 1.6 T.& 2013 Elsevier B.V. All rights reserved. 1. IntroductionManganites are manganese compounds of composition AMnO 3 ,where e.g. A¼ La, Ca, Ba,y, which crystallize in the cubic structureof the so called ‘‘perovskite mineral’’ CaTiO 3 . Depending on thecomposition they show a wide variety of magnetic and electricphenomena, including ferromagnetic, antiferromagnetic, chargeand orbital ordering. The multiferroic behavior and magnetoresis-tive effects make such oxides as natural candidates for potentialspintronics applications [1,2]. Intrinsic anisotropy is induced if theA site is occupied by different types of ions, with e.g. differentintrinsic charges. When the site A is partially or fully occupied by amagnetic ion, a severe intrinsic anistropy may be induced and thecompounds show different anisotropic behaviors as the tempera-ture is changed. This is considerable if the A ion has an f-shell, likein the rare earth ions. It is easily guessed that such anisotropicfeatures will surely depend on the orientation of any appliedmagnetic field.The perovskites manganites where A is a rare-earth (RE)element present the coexistence of magnetism and ferroelectricity.Moreover, either orthorhombic or hexagonal REMnO

Magnetic and electrical properties of electron-doped manganites Ca0.88Ce0.12MnO3 and Ca0.90Ce0.10MnO3 were studied in pulsed magnetic fields up to 60 T in the temperature range T = 1.5–260 K. Metamagnetic transition caused by the melting of the charge/orbital ordering and martensitic structural transition in a magnetic field was revealed. The transition is accompanied by a change in electrical resistivity of the sample by three orders. A magnetic phase diagram in the plane of the H–T was constructed. Higher values of the critical transition fields for the system Ca1−xCexMnO3, compared to the known system Ca1−xSmxMnO3 are explained by a narrower range of phase separation and a bigger difference between the Neel temperatures of the C and G-type antiferromagnetic phases, which originated from the difference between the valence of the Ce4+ and Sm3+ ions.

We report accurate measurements of the resistive transition in two different polycrystalline samples of superconducting MgB2. The results are described in terms of the temperature derivative of the resistivity, d ?/d T. A method is developed to analyse these data. A structure consisting of two closely separated maxima is observed in d ?/d T near the transition. This splitting is suppressed by applying magnetic fields above 10?kOe parallel to the current orientation. We discuss the possible mechanisms underlying the split resistive transition observed in our samples.

We have studied the temperature dependence of the upper critical fields ${\ensuremath{\mu}}_{0}{H}_{c2}$ of ${K}_{x}{\mathrm{Fe}}_{2\ensuremath{-}y}{\mathrm{Se}}_{2\ensuremath{-}z}{S}_{z}$ single crystals up to 60 T. The ${\ensuremath{\mu}}_{0}{H}_{c2}$ for $H\ensuremath{\parallel}ab$ and $H\ensuremath{\parallel}c$ decrease with increasing sulfur content. The detailed analysis using Werthamer-Helfand-Hohenberg theory including the Pauli spin-paramagnetic effect shows that ${\ensuremath{\mu}}_{0}{H}_{c2}$ for $H\ensuremath{\parallel}ab$ is dominated by the spin-paramagnetic effect, which diminishes with higher S content, whereas ${\ensuremath{\mu}}_{0}{H}_{c2}$ for $H\ensuremath{\parallel}c$ shows a linear temperature dependence with an upturn at high fields. The latter observation can be ascribed to multiband effects that become weaker for higher S content. This results in an enhanced anisotropy of ${\ensuremath{\mu}}_{0}{H}_{c2}$ for high S content due to the different trends of the spin-paramagnetic and multiband effect for $H\ensuremath{\parallel}ab$ and $H\ensuremath{\parallel}c$, respectively.

We report on Hall effect, longitudinal resistivity and magnetization measurements in the rutheno-cuprate RuSr 2 GdCu 2 O 8 . Combining these results we separate the anomalous contribution to the Hall effect and argue that the occurrence of canting and chirality have to be considered for describing this property.

We report an angle-dependent study of the magnetic torque $\tau(\theta)$ within the vortex state of single-crystalline LaO$_{0.9}$F$_{0.1}$FeAs and SmO$_{0.9}$F$_{0.1}$FeAs as a function of both temperature $T$ and magnetic field $H$. Sharp peaks are observed at a critical angle $\theta_c$ at either side of $\theta=90^{\circ}$, where $\theta$ is the angle between $H$ and the inter-planar \emph{c}-axis. $\theta_c$ is interpreted as the critical depinning angle where the vortex lattice, pinned and locked by the intrinsic planar structure, unlocks and acquires a component perpendicular to the planes. We observe a series of smaller replica peaks as a function of $\theta$ and as $\theta$ is swept away from the planar direction. These suggest commensurability effects between the period of the vortex lattice and the inter-planar distance leading to additional kinked vortex configurations., Comment: 5 pages, 5 figures

We observe a bilinear magnetic field-induced electric polarization of 50 $\mu C/m^2$ in single crystals of NiCl$_2$-4SC(NH$_2$)$_2$ (DTN). DTN forms a tetragonal structure that breaks inversion symmetry, with the highly polar thiourea molecules all tilted in the same direction along the c-axis. Application of a magnetic field between 2 and 12 T induces canted antiferromagnetism of the Ni spins and the resulting magnetization closely tracks the electric polarization. We speculate that the Ni magnetic forces acting on the soft organic lattice can create significant distortions and modify the angles of the thiourea molecules, thereby creating a magnetoelectric effect. This is an example of how magnetoelectric effects can be constructed in organo-metallic single crystals by combining magnetic ions with electrically polar organic elements., Comment: 3 pages, 3 figures

We report measurements of the temperature dependence of the radio-frequency magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T. From our data, we construct an H-T phase diagram for the inter-plane (H || c) and in-plane (H || ab) directions for both compounds. For both field orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the Hc2(T) lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we can describe Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped compound, the data support a Hc2(T) dependence that can be described by the Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H || c., Comment: 7 pages, 8 figures

We report on the study of the Fermi surface of the electron-doped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_{4}$ by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of $x=0.13$ to 0.17. In the overdoped regime of $x > 0.15$ we found both semiclassical angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas (SdH) oscillations. The combined AMRO and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply-connected Fermi surface up to the very end of the overdoped regime at $x\simeq 0.17$. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime., 23 pages, 8 figures

Early work on the iron-arsenide compounds supported the view, that a reduced dimensionality might be a necessary prerequisite for high-Tc superconductivity. Later, however, it was found that the zero-temperature upper critical magnetic field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we report measurements of the temperature dependence of the electrical resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and pulsed magnetic fields up to 60 T. We find that the resistivity of both compounds in zero field is well described by an exponential term due to inter-sheet umklapp electron-phonon scattering between light electrons around the M point to heavy hole sheets at the \Gamma point in reciprocal space. From our data, we construct an H-T phase diagram for the inter-plane (H || c) and in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic in optimally doped samples down to low temperatures. The anisotropy parameter, {\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find a concave curvature of the Hc2 lines with decreasing anisotropy and saturation towards lower temperature. Taking into account Pauli spin paramagnetism we perfectly can describe Hc2(T) and its anisotropy., Comment: 7 pages, 3 figures

We report on semiclassical angle-dependent magnetoresistance oscillations and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd(2-x)CexCuO4. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime.

The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing $S=1/2$ Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures.

Neutron diffraction is used to investigate the field-induced, antiferromagnetically ordered state in the two-leg spin-ladder material (Hpip)2CuBr4. This “classical” phase, a consequence of weak interladder coupling, is nevertheless highly unconventional: its properties are influenced strongly by the spin Luttinger-liquid state of the ladder subunits. We determine directly the order parameter (transverse magnetization), the ordering temperature, the spin structure, and the critical exponents around the transition. We introduce a minimal microscopic model for the interladder coupling and calculate the quantum fluctuation corrections to the mean-field interaction.

The Hall effect has been studied in a series of AuFe samples in the re-entrant concentration range, as well as in part of the spin glass range. An anomalous Hall contribution linked to the tilting of the local spins can be identified, confirming theoretical predictions of a novel topological Hall term induced when chirality is present. This effect can be understood in terms of Aharonov-Bohm-like intrinsic current loops arising from successive scatterings by canted local spins. The experimental measurements indicate that the chiral signal persists, meaning scattering within the nanoscopic loops remains coherent, up to temperatures of the order of 150 K., 7 pages, 11 eps figures Published version. Minor changes

The extraordinary Hall effect coefficients $R_s(T)$ of the canonical spin glass alloys ${\bf Au}Fe 8 at\%$ and ${\bf Au}Mn 8 at\%$ and of an archetype reentrant system ${\bf Au}Fe 18 at\%$ were measured as functions of temperature. The data show a critical cusp-like term superimposed on a smooth background for the spin glasses, and change of sign with temperature for the reentrant. The results can be interpreted consistently by invoking a chiral Hall effect contribution as proposed by Kawamura.

We have made systematic measurements of the anomalous Hall effect in a PdFe and AuFe alloys. The Hall coefficient Rh has been measured as a function of applied magnetic field and temperature. The experimental results demonstrate that it is necessary to consider a negative contribution in addition to the canonical Karplus–Luttinger term. This difference term can be identified to the theoretically predicted chiral or real space Berry phase term and can be understood in terms of the Aharonov–Bohm-like intrinsic microscopic current loops arising from successive scatterings by canted local spins.

The study of multiferroic (MF) and magnetoelectric (ME) materials seeks to understand and harness the coupling between electric and magnetic polarizations. To date, research into ME and MF bulk materials has largely focused on inorganic oxides and only a relatively small number of materials have been found with significant ME couplings. We explore organo-metallics where transition metal ions are incorporated into a flexible and designable organic lattice. We present recent results on ME and MF behavior in single crystals of the organo-metallic compounds NiCl2-4SC(NH2)2 and CuCl2-2(CH3)2SO.

Recently the natural mineral Azurite has been proposed as model substance for the distorted S = ? diamond chain in the spin fluid state. Azurite has alternating doublet monomers and singlet dimers along the chains yielding plateau-like features in the magnetization curves. Although Azurite was also reported to order antiferromagnetically at 1.86 K, the detailed phase diagram and its relationship to the 1/3 plateau is largely unknown. In the present paper, we report preliminary results from a dilatometry study on Azurite carried out in the 0.05 ? 2.30 K temperature range at magnetic fields up to 31 T. It is shown that sizable structural distortions accompany the magnetic ordering and that at 100 mK the long range order between monomers is suppressed precisely at the transition field where the 1/3 plateau sets in.

The magnetocaloric effect in magnetic materials is of great interest nowadays. In this article we present an investigation about the magnetic properties near the magnetic transition in a polycrystalline sample of a manganite Tb0.9Sn0.1MnO3. Particularly, we are interested in describing the nature of the magnetic interactions and the magnetocaloric effect in this compound. The temperature dependence of the magnetization was measured to determine the characteristics of the magnetic transition and the magnetic entropy change was calculated from magnetization curves at different temperatures. The magnetic solid is paramagnetic at high temperatures. We observe a dominant antiferromagnetic interaction below Tn=38 K for low applied magnetic fields; the presence of Sn doping in this compound decreases the Neel temperature of the pure TbMnO3 system. A drastic increase in the magnetization as a function of temperature near the magnetic transition suggests a strong magnetocaloric effect. We found a large magnetic en...