Geologic mapping and basement–sediment contact delineation along Profile X, Igarra–Auchi area, Southern Nigeria using ground magnetic and electromagnetic methods

Outcrop mapping as well as electromagnetic and ground magnetic surveys was carried out within Auchi and Igarra localities in order to attempt an interpretation of the geology of the areas and to delineate the boundary between basement and sedimentary terrains. Geologic mapping was done by collecting samples of outcrops at five different locations within the areas. Three lithofacies were identified within Auchi area and they are the basal shale unit, tabular cross-bedded sandstone unit and ferruginized sandstone unit. The pebbly shale is greyish black in colour; the cross-bedded sandstone unit is greyish white, coarse-grained at the base and finer at the top with pockets of clay, while the ferruginized sandstone is dark red. Rocks of the Precambrian basement complex underlie Igarra area. The area is underlain by metasediments that have been intruded by igneous rocks. Results show the presence of three major groups of igneous and metamorphic rocks within the area, and they are the migmatite–gneiss complex, metasediments and porphyritic granites. The electromagnetic and ground magnetic data acquired along Profile X located along Auchi–Igarra–Ibillo road were processed using Microsoft Excel Software and the resulting plots delineated areas with lower electrical conductivities and higher magnetic susceptibilities, as well as areas with higher electrical conductivities and lower magnetic susceptibilities. The areas with lower electrical conductivities and higher magnetic susceptibilities are interpreted to be underlain by basement rocks, while the areas with higher electrical conductivities and lower magnetic susceptibilities are underlain by sedimentary rocks. The plots also delineated the most likely basement–sedimentary boundary in the area.

Effect of Controlled Artificial Disorder on the Magnetic Properties of EuFe2(As1-xPx)2 Ferromagnetic Superconductor

Static (DC) and dynamic (AC, at 14 MHz and 8 GHz) magnetic susceptibilities of single crystals of a ferromagnetic superconductor, EuFe2(As1−xPx)2 (x = 0.23), were measured in pristine state and after different doses of 2.5 MeV electron or 3.5 MeV proton irradiation. The superconducting transition temperature, Tc(H), shows an extraordinarily large decrease. It starts at Tc(H=0)≈24K in the pristine sample for both AC and DC measurements, but moves to almost half of that value after moderate irradiation dose. Remarkably, after the irradiation not only Tc moves significantly below the FM transition, its values differ drastically for measurements at different frequencies, ≈16 K in AC measurements and ≈12 K in a DC regime. We attribute such a large difference in Tc to the appearance of the spontaneous internal magnetic field below the FM transition, so that the superconductivity develops directly into the mixed spontaneous vortex-antivortex state where the onset of diamagnetism is known to be frequency-dependent. We also examined the response to the applied DC magnetic fields and studied the annealing of irradiated samples, which almost completely restores the superconducting transition. Overall, our results suggest that in EuFe2(As1−xPx)2 superconductivity is affected by local-moment ferromagnetism mostly via the spontaneous internal magnetic fields induced by the FM subsystem. Another mechanism is revealed upon irradiation where magnetic defects created in ordered Eu2+ lattice act as efficient pairbreakers leading to a significant Tc reduction upon irradiation compared to other 122 compounds. On the other hand, the exchange interactions seem to be weakly screened by the superconducting phase leading to a modest increase of Tm (less than 1 K) after the irradiation drives Tc to below Tm. Our results suggest that FM and SC phases coexist microscopically in the same volume.

Copper(II) Carboxylates with 2,3,4-Trimethoxybenzoate and 2,4,6-Trimethoxybenzoate: Dinuclear Cu(II) Cluster and µ-Aqua-Bridged Cu(II) Chain Molecule

Copper(II) complexes with 2,3,4-trimethoxybenzoic acid (H234-tmbz) and 2,4,6-trimethoxybenzoic acid (H246-tmbz), [Cu2(234-tmbz)4(H2O)2] (6) and [Cu(246-tmbz)2(µ-H2O)2(H2O)2]n (7), were synthesized and characterized by elemental analysis, infrared and UV-vis spectra and temperature dependence of magnetic susceptibilities (1.9–300 K). The X-ray crystal structures revealed that the former 6 is a dinuclear cluster having syn-syn-bridged Cu2(µ-234-tmbz)4 core with Cu···Cu separation of 2.6009(7) Å, while the latter 7 is a µ-aqua-bridged chain molecule consisting of Cu(246-tmb)2(µ-H2O)2(H2O)2 units with Cu···Cu separation of 4.1420(5) Å. Temperature dependence of magnetic susceptibilities showed that an antiferromagnetic interaction with 2J = −272 cm−1 for 6 and a weak antiferromagnetic interaction with J = −0.21 cm−1 for 7, between the two copper(II) ions. The adsorption isotherm of 6 showed Types I behavior having a 125.4 m2g−1 of specific surface area.

A series of new layered lithium europium(II) oxoniobates(V) and -tantalates(V)

The new Ruddlesden-Popper-related phases An+1BnO3n+1 (n = 3) with the compositions Li2Eu2Nb3O10, Li2Eu1.5Ta3O10, Li2EuKNb3O10, and Li2EuKTa3O10 were synthesized by solid-state reactions from Li2[CO3] (+ K2[CO3]) and the corresponding refractory metals along with their oxides in a high-frequency furnace at temperatures above T = 1600°C. Their structures have been determined by single-crystal X-ray diffraction studies. Characteristic features are triple layers of corner-sharing [MO6]7− octahedra (M = Nb and Ta), which are connected via [LiO4]7− tetrahedra. The Eu2+ cations are cuboctahedrally surrounded by 12 oxygen atoms and according to the Eu–O distances of around 275 pm, they have the oxidation state +2, as confirmed by XPS measurements. In the potassium-containing samples they share their positions with K+ cations. The black compounds are stable in air at room temperature. Measurements of the magnetic susceptibilities in the range of T = 5–300 K revealed Li2Eu2Nb3O10, Li2Eu1.5Ta3O10 and Li2EuKTa3O10 to be paramagnetic without any ordering.