Papers by Keyword: Ferromagnetism

Abstract: We study ultrafast magnetization dynamics induced by laser heating using various phenomenological temperature models. The temperature dynamics of the electrons, spins and lattice for thin foils is investigated. Numerical results for the temperature and magnetization dynamics for them are compared with those available in the literature.

Abstract: The article presents a study of the transport properties of high-temperature superconducting compounds of the Y-Ba-Cu-O system with the addition of the carbon nanomaterial (carbon nanotubes) "Taunite" in different concentrations. According to the data of X-ray phase analysis, scanning electron microscopy and magnetic measurements, it was determined that the carbon nanotube "Taunite" contains ferro-and superparamagnetic particles (~ 30 nm). The dependences of the resistance of the samples on the temperature have been constructed, and the temperature of the transition of the samples to the superconducting state (~ 90 K) has been determined, and the features ("stages") on the resistance curves are observed below. Nickel nanoparticles in the carbon nanotubes "Taunite" have been established to not affect the critical temperature of the superconducting transition, yet after reaching a certain concentration, they destroy the superconducting state.

Abstract: Non-doped and strontium-doped lanthanum cuprates (La₂CuO₄ (LCO) and La_1.85Sr_0.15CuO₄ (LSCO15)) in nano-sized particles were synthesized by the chemically dissolved technique employing HNO₃ as the dissolving agent. The structural and magnetic properties were investigated by using an x-ray diffraction (XRD) apparatus and a superconducting quantum interference device (SQUID) magnetometer, respectively. The XRD patterns of LCO and LSCO15 show the formation of the single phase without impurities after the calcinations in air at 1100°C for 15 h and the post-annealing in oxygen at 800 °C for 24 h. The average crystallite sizes of LCO and LSCO15 samples were in a range of around 100 nm confirming nano-sized particles. The LCO and LSCO15 nanoparticles exhibit superconductivity at the superconducting (SC) transition temperature, T_c, of 23 K and 38 K, respectively. The magnetization curve measurements have revealed that both samples show the appearance of ferro- and dia-magnetic behavior at room temperature and the appearance of superconductivity at low temperatures. This result may indicate the coexistence of ferromagnetism and superconductivity below T_c in the nano-sized cuprates.

Abstract: The coexistence of ferromagnetism and paramagnetism of T’-Pr_2-xCe_xCuO_4+α-δ (T’-PCCO) nanoparticles with x = 0, and 0.10 have been studied intensively in the normal state. All samples were synthesized by a chemically dissolved method using HNO₃ as a dissolving agent. The calcination process was performed at 1000°C for 15 h in air and followed by reduction annealing at 700°C in argon atmosphere for 10 h. All samples were first characterized by an x-ray diffraction (XRD) measureemnts followed by Rietveld and Maximum Entropy Method (MEM) analyseis. The result confirms the Ce-dependence and reduction annealing effect on the electron density at around the Cu site. The magnetic characterization was performed by using vibration sample magnetometer (VSM) indicating weak ferromagnetic properties at x = 0 and dominant paramagnetic properties at x = 0.10 at room temperature. Moreover, the weak ferromagnetic feature seems to remain after the annealing process. This signifies the coexist of weak ferromagnetism and paramagnetism at the normal state due to a number of oxygen vacancies in the crystal structure.

Abstract: The preparation methods of high performance ferromagnetic sputtering targets (including cobalt, nickel-platinum and nickel-iron alloy) for advanced semiconductor manufacturing were introduced. The properties of sputtering target, such as pass-through-flux (PTF), and grain size which affect the sputtering performance were well controlled by proper fabrication technique. The key factors that affect sputtering performance were also discussed.

Abstract: The optimization of magnetic uses of magnetic garnet type ferrites is largely known depending on their microstructure, synthesis process and chemical composition of the materials. This research investigates the effect of dopants substitution on microstructure and magnetic properties of Yttrium Iron Garnet (YIG). The oxide-mixture route was employed in synthesizing the YIG powders using Aluminium and Lanthanum as dopants with concentration of 0.5 prior to sintering at 1400 °C. The samples were characterized in several testing applications in order to study the structural, microstructural, magnetic properties and density effects toward the samples workability as ferromagnetic materials. Characterization of the samples were carried out by using Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), Impedance/Materials Analyzer and density measurement. The results showed that La-doped YIG shows an incredible achievement as a new ferromagnetic material, meanwhile with the substitution of Aluminum ion would increase the magnetic response of YIG.

Abstract: MnGeAs₂ thin films were successfully deposited on GaAs(100) substrate. The films exhibited room-temperature ferromagnetism with T_C ~ 330 K, based on both magnetization and resistance measurements at temperatures from 5 to 370 K. The coercive fields at 5 and 300 K were 2100 and 50 Oe. The anomalous Hall effect was observed, suggesting the existence of spin polarized carriers in MnGeAs₂ thin films. The magnetoresistance (MR) measurements showed very small change (~ 0.1% at 5 K) in resistance at low temperature. The MR value at 5 K was smaller than that (~ 9% at 305 K) at room temperature (305 K). Type of majority carriers in the films was determined to be n-type by Hall measurement above the transition temperature. The effective carrier density was 1.8´10²⁰ cm^-3. The diode current-voltage characteristics were shown in a hetero-junction MnGeAs₂ film on a conducting p-type GaAs substrate.

Abstract: We report on the magnetoelectric properties of Er₂CoMnO₆. This compound adopts the structure of a double perovskite with a strong monoclinic distortion. Our specimen exhibits a nearly perfect Co-Mn order. It undergoes a ferromagnetic transition at T_C~70 K due to the Co²⁺-O-Mn⁴⁺ ferromagnetic superexchange interaction. Below 30 K, the Er³⁺ moments start to order antiferromagnetically to the Co/Mn sublattice. Pyroelectric measurements reveal electrical polarization at low temperature but its strong dependence on the heating rate indicates the lack of a spontaneous ferroelectricity. Instead, electric polarization is derived from thermally stimulated depolarization currents.

Abstract: Pass through flux (PTF) is an essential parameter for the magnetron sputtering process of ferromagnetic materials. In the present investigation the influence of deformation, recrystallized microstructure and thickness on PTF of Ni was examined by the analysis of microstructure and hardness of high purity Ni. The experimental results showed that PTF of rolled Ni increased significantly comparing to the annealing microstructure that is related to the dislocation and stress of microstructure. With the recrystallization and grain growth of deformed samples, PTF decreased to be about 30%. PTF was also associated with the thickness of material. It increased by 6% when the thickness of 0.5mm decreased. This research is useful to guide and improve the design, development and preparation of magnetic sputtering materials.

Abstract: Intermetallic alloys and compounds undergoing diffusionless solid–solid phase transformations are an important class of high-damping materials. Some representatives of these alloys and compounds also possess good magnetic properties. For such materials, a combination of the magnetoelastic coupling and a high mobility of the martensitic variants can bring about new features of the internal friction and allows one to control the damping capacity by an external magnetic field. Here we review damping properties of magnetically ordered shape memory alloys.