Magnetic Characteristics of Mn-Implanted GaN Nanorods Followed by Thermal Annealing

We have investigated the magnetic and optical properties of dislocation-free vertical GaN nanorods with diameters of 150 nm grown on (111) Si substrates by radio-frequency plasma-assisted molecular-beam epitaxy followed by Mn ion implantation and annealing. The GaN nanorods are fully relaxed and have a very good crystal quality characterized by extremely strong and narrow photoluminescence excitonic lines near 3.47 eV. For GaMnN nanorods, it can be concluded that the ferromagnetic property of GaMnN nanorod with a Curie temperature over 300 K is associated with the formation of Mn 4 Si 7 magnetic phase which results from the effects of magnetic and structural disorder introduced by a random incorporation and inhomogeneous distribution of Mn atoms in the porous layer between the nanorods that form precipitates in the Si substrate before or during the annealing step amongst the GaN nanorods

Specific heat study of Ga1-xMnxAs

Specific heat measurements were used to study the magnetic phase transition in Ga1-xMnxAs. Two different types of Ga1-xMnxAs samples have been investigated. The sample with a Mn concentration of 1.6% shows insulating behavior, and the sample with a Mn concentration of 2.6% is metallic. The temperature dependence of the specific heat for both samples reveals a pronounced lambda-shaped peak near the Curie temperature, which indicates a second-order phase transition in these samples. The critical behavior of the specific heat for Ga1-xMnxAs samples is consistent with the mean-field behavior with Gaussian fluctuations of the magnetization in the close vicinity of TC.Comment: 12 pages, 5 figure

Радиопоглощающие материалы на основе наполненного полиэтилена

Радиопоглощающие материалы (РПМ) и электромагнитные экраны на их основе являются одним из эффективных средств решения проблем электромагнитной безопасности и электромагнитной совместимости радиоэлектронной техники. Среди многообразия РПМ свою нишу занимают материалы на основе наполненного полиэтилена. Для композитных РПМ на основе полиэтилена, содержащего различные функциональные дисперсные наполнители и армированные электропроводящими тканями, установлены оптимальные значения толщины образцов, степени наполнения, при которых ослабление энергии СВЧ-излучения максимально. Оценены радиофизические параметры полимерных композитных РПМ в диапазоне частот 2,0–27,0 ГГц при нормальном падении на образец электромагнитной волны. С применением растровой электронной микроскопии изучена структура композитных РПМ. По технологическим и технико-экономическим критериям наиболее перспективными средствами радиозащиты являются РПМ на основе функционально наполненных термопластов. РПМ относятся к материалам двойного назначения и могут быть использованы при создании малозаметных объектов, в том числе летательных аппаратов.Radioabsorbing materials and electromagnetic screen based on these materials are one of the effective means of solving electromagnetic safety and electromagnetic compatibility problems of radioelectronic equipment. Among the variety of radioabsorbing materials loaded polyethylene based materials hold their own place. For composite radioabsorbing materials based on polyethylene including various functional dispersed fillers and reinforced with conducting textiles optimum thickness values of the samples are specified and also the levels of filling at which the attenuation of microwave radiation reaches maximum. Radio physical parameters of polymer composite radioabsorbinhg materials in the range of frequencies of 2,0–27,0 GHz at normal incidence of electromagnetic wave on a sample are evaluated. Using raster electronic microscopy the structure of composite radioabsorbing materials have been studied. Evaluated by technological and technical-economic parameters the most promising means of radioprotection are radioabsorbing materials based on functionally loaded thermoplastic materials. Radioabsorbing materials are referred to as double-purpose materials and can be used for making barely visible objects such as flying apparatuses

Strong Room-Temperature Ferromagnetism of MoS₂ Compound Produced by Defect Generation

Ferromagnetic materials have been attracting great interest in the last two decades due to their application in spintronics devices. One of the hot research areas in magnetism is currently the two-dimensional materials, transition metal dichalcogenides (TMDCs), which have unique physical properties. The origins and mechanisms of transition metal dichalcogenides (TMDCs), especially the correlation between magnetism and defects, have been studied recently. We investigate the changes in magnetic properties with a variation in annealing temperature for the nanoscale compound MoS2. The pristine MoS2 exhibits diamagnetic properties from low-to-room temperature. However, MoS2 compounds annealed at different temperatures showed that the controllable magnetism and the strongest ferromagnetic results were obtained for the 700 °C-annealed sample. These magnetizations are attributed to the unpaired electrons of vacancy defects that are induced by annealing, which are confirmed using Raman spectroscopy and electron paramagnetic resonance spectroscopy (EPR)

Effects of Thermal Annealing on Optical and Microscopic Ferromagnetic Properties in InZnP:Ag Nano-Rods

InZnP:Ag nano-rods fabricated by the ion milling method were thermally annealed in the 250~350 °C temperature range and investigated the optimum thermal annealing conditions to further understand the mutual correlation between the optical properties and the microscopic magnetic properties. The formation of InZnP:Ag nano-rods was determined from transmission electron microscopy (TEM), total reflectivity and Raman scattering analyses. The downward shifts of peak position for LO and TO modes in the Raman spectrum are indicative of the production of Ag ion-induced strain during the annealing process of the InZnP:Ag nano-rod samples. The appearance of two emission peaks of both (A0 X) and (e, Ag) in the PL spectrum indicated that acceptor states by Ag diffusion are visible due to the effective incorporation of Ag-creating acceptor states. The binding energy between the acceptor and the exciton measured as a function of temperature was found to be 21.2 meV for the sample annealed at 300 °C. The noticeable MFM image contrast and the clear change in the MFM phase with the scanning distance indicate the formation of the ferromagnetic spin coupling interaction on the surface of InZnP:Ag nano-rods by Ag diffusion. This study suggests that the InZnP:Ag nano-rods should be a potential candidate for the application of spintronic devices

Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1-x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1-x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1-x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states

Room temperature transparent conducting magnetic oxide (TCMO) properties in heavy ion doped oxide semiconductor

Bismuth doped ZnO (ZnBi0.03O0.97) thin films are grown using pulsed laser deposition. The existence of positively charged Bi, absence of metallic zinc and the Zn-O bond formation in Bi doped ZnO are confirmed using X-ray Photoelectron Spectroscopy (XPS). Temperature dependent resistivity and UV-visible absorption spectra show lowest resistivity with 8.44 × 10-4 Ω cm at 300 K and average transmittance of 93 % in the visible region respectively. The robust ferromagnetic signature is observed at 350 K (7.156 × 10-4 emu/g). This study suggests that Bi doped ZnO films should be a potential candidate for spin based optoelectronic applications