Preparation of PSFO and LPSFO Nanofibers by Electrospinning and Their Electronic Transport and Magnetic Properties

In this paper, Pr0.5Sr0.5FeO3 (PSFO) and La0.25Pr0.25Sr0.5FeO3 (LPSFO) nanofibers were prepared by electrospinning and subsequent calcination, and their morphology, microstructure, electronic transport and magnetic properties were studied systematically. The temperature-dependent resistance curves of PSFO and LPSFO nanofibers were measured in the temperature range from 300 K down to 10 K. With the temperature lowering, the resistance increased gradually and the then decreased sharply due to the occurrence of ferromagnetic metal phase. The metal-insulator transition temperature was about 110 K and 180 K for PSFO and LPSFO nanofibers separately. The electronic conduction behavior above the transition temperature can be described by one-dimensional Mott’s variable-range hopping (VRH) model. The hysteresis loops and the field-cooled (FC) and zero-field-cooled (ZFC) curves showed that both PSFO and LPSFO nanofibers exhibit ferromagnetism. Although the doping of La reduces the overall magnetization intensity of the material, it increases the ferromagnetic ratio of the system, which may improve the performance of LPSFO in solid oxide fuel cell.

Aeromagnetic survey in Kusatsu-Shirane volcano, central Japan, by using an unmanned helicopter

Kusatsu-Shirane volcano is one of the active volcanoes in Japan. Phreatic explosions occurred in Mt. Shirane in 1983 and most recently, in 2018, in Mt. Motoshirane. Information on the subsurface structure is crucial for understanding the activity of volcanoes with well-developed hydrothermal systems where phreatic eruptions occur. Here, we report aeromagnetic surveys conducted at low altitudes using an unmanned helicopter. The survey aimed to obtain magnetic data at a high spatial resolution to map the magnetic anomaly and infer the magnetization intensity distribution in the region immediately after the 2018 Mt. Motoshirane eruption. The helicopter used in the survey was YAMAHA FAZER R G2, an autonomously driven model which can fly along a precisely programmed course. The flight height above the ground and a measurement line spacing were set to ~ 150 m and ~ 100 m, respectively, and the total flight distance was 191 km. The measured geomagnetic total intensity was found to vary by ~ 1000 nT peak-to-peak. The estimated magnetization intensity derived from measured data showed a 100 m thick magnetized surface layer with normal polarity, composed of volcanic deposits of recent activities. Underneath, a reverse-polarity magnetization was found, probably corresponding to the Takai lava flow in the Early Quaternary period (~ 1 Ma) mapped in the region. Our results demonstrate the cost-effectiveness and accuracy of using drone magnetometers for mapping the rugged terrain of volcanoes.

Parameter Identification and Linear Model of Giant Magnetostrictive Vibrator

A linear magnetization model is built to replace the Jiles–Atherton model in order to describe the relationship between the magnetic field intensity and the magnetization intensity of the giant magnetostrictive vibrator (GMV). The systematic modeling of the GMV is composed of three aspects, i.e., the structural mechanic model, the magnetostrictive model, and the Jiles–Atherton model. The Jiles–Atherton model has five parameters to be defined; hence, its solution is so complex that it is not convenient in application. Therefore, the immune genetic algorithm (IGA) is applied in the identification of the five parameters of the Jiles–Atherton model and it showed a higher stability compared with the identification result of the differential evolution algorithm (DEA). The identification parameters of the two algorithms were employed, respectively, to calculate the excitation force and it was found that the relative error of IGA was evidently smaller than that of DEA, indicating that the former was more reliable than the latter. According to the identification results of IGA and based on the least square method (LSM), curve-fittings to the magnetic field intensity and magnetization intensity were conducted by using the linear function. And the linear magnetization model was built to replace the Jiles–Atherton model. Research results show that the linear model of the GMV can be established by combining the linear magnetization model with the structural mechanic model as well as the giant magnetostrictive model. The linear magnetization model, which has great engineering application value, can be applied in the open-loop control of the vibrator.

Magnetic amplitude inversion for depth-to-basement and apparent magnetization-intensity estimates

We have developed an inversion method to recover the depth and the total magnetization intensity of the basement under a sedimentary basin using the amplitude of the magnetic anomaly vector (amplitude data). Because the amplitude data are weakly dependent on the magnetization direction, our method is suitable for interpreting areas with remanent magnetization. Our method assumes constant magnetized basement rocks overlain by nonmagnetic sediments. To overcome the inherent ambiguity of potential field data, we assume knowledge of the average depth of the basement and use it as a constraint to regularize the inversion. A sensitivity analysis with synthetic data shows the weak dependency of the magnetic amplitude inversion on the magnetization direction. Different combinations of magnetization directions recover the interface separating sediments from basement rocks. Test on field data over the Foz do Amazonas Basin, Brazil, recovers the shape of the basement relief without any knowledge about the magnetization intensity and direction. The estimated basement relief reveals a smooth basement framework with basement highs in the central part of the area. In a regional-scale perspective, the deeper and constant estimated basement relief at the northernmost limit of the area may suggest changing in crustal domains from a hyperextended continental crust to homogeneous oceanic crust.

A novel graphene-based Fe3O4 nanocomposite for magnetic particle inspection

The magnetic particle material is the crucial part in the field of nondestructive inspection. Nevertheless, traditional magnetic particle still leaves much to be desired. In this research, we designed a simple procedure to synthesize a novel graphene-based ferroferric oxide (Fe3O4) nanocomposite. All characterizations implied that Fe3O4 was anchored on the surface of reduced graphene oxide (RGO) nanosheets successfully. Especially this specimen reveals significant magnetic property improvement and macroscopic stability because of the synergistic effect between Fe3O4 and graphene, as compared to the traditional magnetic particle. More importantly, our method optimizes intrinsic magnetization intensity, reduces remanence and sedimentation velocity of magnetic particle material. Thus, this nanocomposite holds great potential for the field of magnetic particle inspection.

New constraints on the tectonic activity of the “Tellian Domain” from Northern Tunisia: preliminary paleomagnetic results.

<p>In this study, we present preliminary results on paleomagnetic data collected in the Tunisian Tellian domain in both magmatic and sedimentary rocks of middle to lat Miocene ages from the Nefza-Mogods province, North-West of Tunisia. About 320 cores distributed over twenty one sites were collected both in magmatic rocks (16 sites) and in sedimentary rocks (5 sites), in order to obtain geometric constraints to establish a kinematic model along the North-East African margin. The sampled rocks are distributed between basanites, rhyodacites and microgranites. Some samples were taken from host sedimentary rocks host rocks in lacustrine limestones and jaspilites. Demagnetization process and Rock-Magnetism studies revealed a diversified magnetic mineralogy. In basalts, magnetite with an unblocking temperature of 580 °C is identified. In rhyodacites, the mineralogy is mixed with three types of minerals: a mineral with an unblocking temperature around 350°-400°C attributed either to a sulfide or to titanomagnetite, magnetite with unblocking temperature at 580°C, and a high temperature mineral with unblocking temperature between 600°C and 680°C attributed to hematite or titanohematite. The limestones, having a low magnetization intensity, are characterized by the presence of magnetite and the jaspilites by hematite. Basalts, which have been mainly demagnetized by AF process , show a characteristic component demagnetized between 20mT and 100mT. For rhyodacites, some sites have a characteristic component demagnetized between 400°C and 580°C and others up to 670°C. Although their low magnetization intensity, the lacustrine limestones show a magnetic component between 20mT and 140 mT. The first result indicate that the mean directions associated to the younger magmatic (basalts and rhyodacite) rocks (8 Ma, Tortonian) and their sedimentary host deposits are very close to the expected magnetic field after tilting in paleogeographic coordinates. By contrast, the older microgranites and rhyodacites(-12 Ma) display a vertical axis clockwise rotation of about 30°. This result suggests a significant tectonic phase between 12 Ma and 8 Ma, linked to the implementation of the Tell nappes.</p>