An organic plastic ferroelectric with high Curie point

An organic plastic ferroelectric, (−)-Camphanic acid, shows multiaxial ferroelectric feature and large entropy gain during the phase transition.

Synthesis of bulk crystals and thin films of the ferromagnetic MnSb

High-temperature ferromagnets are widely used on a practical level. Based on them, magnetic memory for computers and various types of magnetic field sensors are created. Therefore, bulk ingots and thin-film samples of ferromagnet manganese antimonide (MnSb) with a high Curie point are of great interest, both from the practical and fundamental sides. Manganese antimonide films are obtained in hybrid structures using molecular-beam epitaxy. The thickness of the films does not exceed tens of nanometers. Despite their high sensitivity to magnetic fields, their small thickness prevents them from being used as magnetic field sensors. The aim of this work was to synthesise thick bulk ingots of manganese antimonide crystalsand films with a thickness of ~ 400 nm on sitall and silicon substrates. MnSb crystals were synthesised using the vacuum-ampoule method and identified using XRD, DTA, and microstructural analysis. The results of studies of bulk samples indicated the presence of an insignificant amount of antimony in additionto the MnSb phase. According to the DTA thermogram of the MnSb alloy, a small endothermic effect was observed at 572 °C, which corresponds to the melting of the eutectic on the part of antimony in the Mn-Sb system. Such composition, according to previous studies, guaranteed the production of manganese antimonide with the maximum Curie temperature. A study of the magnetic properties showed that the synthesised MnSb crystals were a soft ferromagnet with the Curie point ~ 587 K. Thin MnSb films were obtained by an original method using separate sequential deposition in a high vacuum of the Mnand Sb metals with their subsequent annealing. To optimise the process of obtaining films with stoichiometric composition, the dependences of the thickness of metal films on the parameters of the deposition process were calculated. The temperature range of annealing at which the metals interact with the formation of ferromagnetic MnSb films was established, the films were identified, and their electrical and magnetic properties were measured

The Depth to Magnetic Sources in the Arctic and Its Relationship with Some Parameters of the Lithosphere

––The depth to magnetic sources in twenty Arctic tectonic provinces is determined from azimuthally averaged Fourier power spectra of geomagnetic anomalies according to the EMAG2v3 and WDMAM 2.0 global models. The resulting depths to the centroid and bottom of the magnetic lithosphere are more reliable than the depth to the upper magnetic boundary. The depth to the bottom of magnetic sources, corresponding to the Curie point depth, varies from 25.3 to 38.1 km in different provinces. The Curie point depth estimates are correlated with several parameters of the lithosphere. They are directly proportional to the lithospheric thickness and inversely proportional to average upper mantle temperatures, but the relationship with the intensity of long-wavelength satellite magnetic anomalies and crustal thickness is poor. The magnetic sources are located at crustal depths in most of the provinces, but the upper mantle may be magnetic beneath deep-water oceanic basins and the Laptev Sea. The results for the Laptev Sea shelf support a passive mechanism of current lithospheric extension in the area.

Precambrian tectonic inheritance control of the NE Brazilian continental margin revealed by Curie point depth estimation

An investigation of Curie point depths (CPD) based on spectral analysis of airborne magnetic data was carried out in the NE Brazilian continental margin. The studied region represents a narrow hyper-extended margin with three sedimentary basins. Regional geothermal gradient and heat flow were also calculated. CPD results were integrated with interpretation of 2D deep seismic data and with estimated isostatic Moho depths. The results reveal that the narrow hyper-extended crust is 150 km wide in the southern sector and 80 km wide in the north, with a narrow ocean-continental transition (OCT) zone that varies from 50 km wide in the south sector to 30 to 20 km wide in the north. The CPD isotherm showed the strong influence of the three main continental blocks of Borborema ́s Shield in the tectonic evolution of the three marginal basins. The CPD analysis corroborated models provided by gravimetric data and successfully demonstrated the sharp control of basement compartments on the thermal properties of the marginal basins domains

Numerical Modeling of Temperature Effect on Tensile Strength of Granitic Rock

The aim of this paper is to numerically predict the temperature effect on the tensile strength of granitic rock. To this end, a numerical approach based on the embedded discontinuity finite elements is developed. The underlying thermo-mechanical problem is solved with a staggered method marching explicitly in time while using extreme mass scaling, allowed by the quasi-static nature of the slow heating of a rock sample to a uniform target temperature, to increase the critical time step. Linear triangle elements are used to implement the embedded discontinuity kinematics with two intersecting cracks in a single element. It is assumed that the quartz mineral, with its strong and anomalous temperature dependence upon approaching the α-β transition at the Curie point (~573 °C), in granitic rock is the major factor resulting in thermal cracking and the consequent degradation of tensile strength. Accordingly, only the thermal expansion coefficient of quartz depends on temperature in the present approach. Moreover, numerically, the rock is taken as isotropic except for the tensile strength, which is unique for each mineral in a rock. In the numerical simulations mimicking the experimental setup on granitic numerical rock samples consisting of quartz, feldspar and biotite minerals, the sample is first heated slowly to a target temperature below the Curie point. Then, a uniaxial tension test is numerically performed on the cooled down sample. The simulations demonstrate the validity of the proposed approach as the experimental deterioration of the tensile strength of the rock is predicted with agreeable accuracy.