Field-induced magnetic phase transitions and correlated electronic states in the hexagonal RAgGe and RPtIn series

Rare earth intermetallic compounds provide rich grounds for investigating the properties of both local moment and strongly correlated, hybridized moment systems. These areas have been intensively explored mostly on cubic and tetragonal intermetallic compounds, and very little work existed on materials with lower symmetry. Moreover, a large number of Ce-based heavy fermion compounds have been studied, whereas the analogous Yb-based ones are much rarer. We thus wanted to study local moment metamagnetism and Yb-based heavy fermion physics in hexagonal systems.;The RAgGe and RPtIn series belonging to the Fe2P family of hexagonal compounds allowed us to perform such studies on both local moment and strongly correlated, hybridized moment systems. The RAgGe and RPtIn compounds presented in this work display anisotropy temperature and field dependent magnetization due to the crystalline electric field (CEF) splitting of the Hund\u27s rule ground state multiplet. The TmAgGe and TbPtIn members of these series display extreme planar anisotropy, which makes them well suited for a study of the angular dependent metamagnetism. We developed the three co-planar Ising-like systems model, which allowed us to determine the net distribution of the magnetic moments in the two compounds.;The YbAgGe and YbPtIn compounds have some properties distinct from the rest of their respective series: having low ordering temperatures and enhanced electronic specific heat coefficient gamma, they can be classified as stoichiometric, Yb-based heavy fermion compounds, with a magnetic field-induced quantum critical point QCP. In the former compound, a non-Fermi liquid-like NFL regime is apparent at intermediate fields, but such a behavior is more ambiguous in the YbPtIn. However, a small Pt-deficiency in flux-grown YbPt0.98In single crystals seems to stabilize, together with the magnetic field, a non-Fermi liquid-like NFL regime.;In summary, TmAgGe and TbPtIn are hexagonal compounds revealing complex, and yet intelligible angular dependent metamagnetism; together with the quantum critical physics found in YbAgGe and YbPtIn, the RAgGe and RPtIn series dramatically confirm the fertile grounds for research that can be found in these hexagonal systems

On the occurrence of type IV solar radio bursts in the solar cycle 24 and their association with coronal mass ejections

Solar activities, in particular coronal mass ejections (CMEs), are often accompanied by bursts of radiation at metre wavelengths. Some of these bursts have a long duration and extend over a wide frequency band, namely, type IV radio bursts. However, the association of type IV bursts with coronal mass ejections is still not well understood. In this article, we perform the first statistical study of type IV solar radio bursts in the solar cycle 24. Our study includes a total of 446 type IV radio bursts that occurred during this cycle. Our results show that a clear majority,∼81% of type IV bursts, were accompanied by CMEs, based on a temporal association with white-light CME observations. However,we found that only∼2.2% of the CMEs are accompanied by type IV radio bursts. We categorised the type IV bursts as moving or stationary based on their spectral characteristics and found that only∼18% of the total type IV bursts in this study were moving type IV bursts. Our study suggests that type IV bursts can occur with both ‘Fast’ (≥500 km/s) and ‘Slow’ (<500 km/s), and also both ‘Wide’(≥60◦) and ‘Narrow’ (<60◦) CMEs. However, the moving type IV bursts in our study were mostly associated with ‘Fast’ and ‘Wide’ CMEs (∼52%), similar to type II radio bursts. Contrary to type II bursts, stationary type IV bursts have a more uniform association with all CME types.Peer reviewe

Point-contact tunneling spectroscopy measurement of Cux_xTiSe2_2: disorder-enhanced Coulomb effects

We performed point-contact spectroscopy tunneling measurements on Cu$_x$TiSe$_2$ bulk with $x=0.02$ and $0.06$ at temperatures ranging from $T=4-40$ K and observe a suppression in the density of states around zero-bias that we attribute to enhanced Coulomb interactions due to disorder. We find that the correlation gap associated with this suppression is related to the zero-temperature resistivity. We use our results to estimate the disorder-free transition temperature and find that the clean limit $T_{c0}$ is close to the experimentally observed $T_c$.Comment: 4 pages, 4 figure

Crystalline electric field of Ce in trigonal symmetry: CeIr3Ge7 as a model case

The crystalline electric field (CEF) of Ce3+ in trigonal symmetry has recently become of some relevance, for instance, in the search of frustrated magnetic systems. Fortunately, it is one of the CEF case in which a manageable analytic solution can be obtained. Here, we present this solution for the general case, and use this result to determine the CEF scheme of the new compound CeIr3Ge7 with the help of T-dependent susceptibility and isothermal magnetization measurements. The resulting CEF parameters B20 = 34.4 K, B40 = 0.82 K and B43 = 67.3 K correspond to an exceptional large CEF splittings of the first and second excited levels, 374 K and 1398 K, and a large mixing between the +-|5/2> and the -+|1/2> states. This indicates a very strong easy plane anisotropy with an unusual small c-axis moment. Using the same general expressions, we show that the properties of the recently reported system CeCd3As3 can also be described by a similar CEF scheme, providing a much simpler explanation for its magnetic properties than the initial proposal. Moreover, a similar strong easy plane anisotropy has also been reported for the two compounds CeAuSn and CePdAl4Ge2, indicating that the CEF scheme elaborated here for CeIr3Ge7 corresponds to an exemplary case for Ce3+ in trigonal symmetry.Comment: 10 pages, 7 figure

Electronic nematic correlations in the stress free tetragonal state of BaFe2−x_{2-x}Nix_{x}As2_{2}

We use transport and neutron scattering to study electronic, structural, and magnetic properties of the electron-doped BaFe$_{2-x}$Ni$_x$As$_2$ iron pnictides in the external stress free detwinned state. Using a specially designed in-situ mechanical detwinning device, we demonstrate that the in-plane resistivity anisotropy observed in the uniaxial strained tetragonal state of BaFe$_{2-x}$Ni$_x$As$_2$ below a temperature $T^\ast$, previously identified as a signature of the electronic nematic phase, is also present in the stress free tetragonal phase below $T^{\ast\ast}$ ($<T^\ast$). By carrying out neutron scattering measurements on BaFe$_2$As$_2$ and BaFe$_{1.97}$Ni$_{0.03}$As$_2$, we argue that the resistivity anisotropy in the stress free tetragonal state of iron pnictides arises from the magnetoelastic coupling associated with antiferromagnetic order. These results thus indicate that the local lattice distortion and nematic spin correlations are responsible for the resistivity anisotropy in the tetragonal state of iron pnictides.Comment: 5 pages, 4 figure

Enhancement of charge-neutral fermionic excitation near spin-flop transition\\ in magnetic Kondo material YbIr3_3Si7_7

The new Kondo material YbIr$_3$Si$_7$, similar to other Kondo insulators, has been reported to exhibit charge-neutral fermionic excitations through measurements of specific heat and thermal conductivity at low temperatures. We performed $^{29}$Si-NMR on YbIr$_3$Si$_7$ to investigate the magnetic response of charge-neutral fermions from a microscopic perspective. In low magnetic fields parallel to the $c$ axis, a single NMR peak in the paramagnetic state splits into three peaks below $T_{\rm N}$. In contrast, only a slight shift of the single NMR peak was observed in high magnetic fields. This spectral change as a function of the $c$-axis magnetic field is interpreted as spin-flop transition, at which the magnetic moments oriented along the $c$ axis (AF-I phase) are rotated to the $ab$ plane with ferromagnetic component along the $c$-axis (AF-II phase). In the vicinity of the spin-flop magnetic field $H_{\rm M}$, nuclear spin-lattice relaxation rate $1/T_1$ was found to be proportional to temperature at low temperatures, indicating the existence of charge-neutral fermions. Furthermore, a peak of $1/T_1$ vs. the $c$-axis magnetic field suggests that the charge-neutral fermions in YbIr$_3$Si$_7$ are closely related to its magnetic properties. Our findings shed light on the origin of charge-neutral fermions in insulators.Comment: 5 pages, 3 figure

Anisotropic Hall Effect in Single Crystal Heavy Fermion YbAgGe

Temperature- and field-dependent Hall effect measurements are reported for YbAgGe, a heavy fermion compound exhibiting a field-induced quantum phase transition, and for two other closely related members of the RAgGe series: a non-magnetic analogue, LuAgGe and a representative, ''good local moment'', magnetic material, TmAgGe. Whereas the temperature dependent Hall coefficient of YbAgGe shows behavior similar to what has been observed in a number of heavy fermion compounds, the low temperature, field-dependent measurements reveal well defined, sudden changes with applied field; in specific for $H \perp c$ a clear local maximum that sharpens as temperature is reduced below 2 K and that approaches a value of 45 kOe - a value that has been proposed as the $T = 0$ quantum critical point. Similar behavior was observed for $H \| c$ where a clear minimum in the field-dependent Hall resistivity was observed at low temperatures. Although at our base temperatures it is difficult to distinguish between the field-dependent behavior predicted for (i) diffraction off a critical spin density wave or (ii) breakdown in the composite nature of the heavy electron, for both field directions there is a distinct temperature dependence of a feature that can clearly be associated with a field-induced quantum critical point at $T = 0$ persisting up to at least 2 K.Comment: revised versio

DETECTION OF HEAVY METALS FROM MOLLUSCS SHELLS

This work presents aspects regarding some heavy metals (Cd, Pb, Cu and Zn) concentration in shells of different molluscs (Mytilus galloprovincialis, Rapana thomasiana, Mya arenaria, Scapharca) collected from the Romanian Black Sea Coast. The heavy metals were analysed using atomic absorption spectrometry