Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures
In this work MnxCo1−xFe2O4 nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm−1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe2O4) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.
Spin-polarized electron transport in highly reduced MgFe2O4-δ
Spin-polarized electron transport is important for spintronics. In this study, MgFe2O4 compound has been reduced by using metallic sodium as a reducing agent and high concentration of oxygen vacancies has been induced in the compound, and the electron transport behavior of a highly-reduced MgFe2O4-δ has been studied in detail. It is found that the room-temperature electrical resistivity of MgFe2O4-δ is decreased by almost 6 orders of magnitude when it is rich in oxygen vacancies (concentration: ∼1021 /cm3). Based on the density functional theory, the band calculations show that the oxygen vacancies can introduce mid-gap states below the upper Hubbard band. The electronic states around the Fermi level are mainly composed of spin-down Fe 3d orbits, indicating highly spin-polarized carriers. Combining with the analysis of the temperature-dependent resistivity, it is demonstrated that the electron transport behavior is mainly dominated by the model of variable-range hopping. It is suggested that the low-temperature reduction is an efficient way to realize the heavily doping of carriers without crystal structure destroying, which provide a new way to turn the electron transport behavior and broaden a potential application of spinel ferrites in spintronic devices.
Computer-Aided System of Virtual Testing of Gas Turbine Engines
The article describes the concept of a virtual lab that includes subsystem of gas turbine engine simulation, subsystem of experiment planning, subsystem of measurement errors simulation, subsystem of simulator identification and others. The basis for virtual lab development is the computer-aided system of thermogasdynamic research and analysis “ASTRA”. The features of gas turbine engine transient modes simulator are described. The principal difference between the simulators of transient and stationary modes of gas turbine engines is that the energy balance of the compressor and turbine becomes not applicable. The computer-aided system of virtual gas turbine engine testing was created using the developed transient modes simulator. This system solves the tasks of operational (throttling, speed, climatic, altitude) characteristics calculation, analysis of transient dynamics and selection of optimal control laws. Besides, the system of virtual gas turbine engine testing is a clear demonstration of gas turbine engine working process and the regularities of engine elements collaboration. The interface of the system of virtual gas turbine engine testing is described in the article and some screenshots of the interface elements are provided. The developed system of virtual gas turbine engine testing provides means for reducing the laboriousness of gas turbine engines testing. Besides, the implementation of this system in the learning process allows the diversification of lab works and therefore improve the quality of training.