Papers by Keyword: Magnetic Semiconductor

Abstract: The co-doping effect of Be and Mn have been studied in the ferromagnetic semiconductor (Ga,Mn)As thin films. The measurement of magnetic properties shows that the Be doping decreases the Curie temperatures of the ferromagnetic sample due to defects formation. The transport studies show that the Be incorporation decreases the resistivity of the (Ga,Mn)As thin films. It is found that Be incorporation decreases the planar Hall resistance but increases the resistance transitions in the magnetic samples.

Abstract: The heterostructure ferromagnetic/semiconductor ZnSiAs2/Si was obtained by using the Si-ZnAs2 phase diagram. The magnetic properties of Zn1-XMnXSiAs2 bulk crystals and ferromagnetic layered heterostructures were similar. The same method was used for preparing a ferromagnetic layer ZnGeAs2 on a germanium substrate.

Abstract: Laser deposition method was used for growing ferromagnetic semiconductor and half-metal compound layers. GaMnAs and InMnAs layers were grown by alternating laser ablation of solid targets (semiconductor and Mn) in hydrogen and arsine flow. The layers exhibited ferromagnetic properties (detected by Hall effect measurements) from 10 K to room temperature (for InMnAs). Half-metal compound layers were deposited by the techniques of reactive laser deposition (MnAs, MnP) and alternating laser deposition (MnSb). The half-metal layers exhibit ferromagnetism at temperatures up to 300 K.

Abstract: The GaAs doped with donors manifests long times of spin relaxation, while in the case of acceptors (or magnetic impurities) spin relaxation rate increases markedly, in accordance with theoretical predictions. From the practical point of view, this situation is unfavorable, since the devices based on spin degrees of freedom require long times of the spin memory. Therefore semiconductors such as p-GaAs were not considered as promising materials for spintronics. In the present work this conclusion is refuted by means of investigation of the spin dynamics of electrons in epitaxial layers of gallium arsenide doped with Mn impurities. In spite of the expectations, we have discovered the suppression of the spin relaxation of electrons in GaAs:Mn by two orders of magnitude. This effect is a consequence of compensation of the hole and manganese effective magnetic fields due to the antiferromagnetic interaction. The analogous results obtained for the case of GaAs quantum well doped with Mn [R. C. Myers, et al., Nature Materials 7, 203 (2008)] were interpreted as the result of the spin precession of magnetic acceptors rather than electrons. Through separate measurements of g-factor by means of time resolved spectroscopy it has been proved that long times of spin relaxation in p-GaAs:Mn relate to electrons and not to magnetic acceptors. The oscillation frequency of the angle of Kerr rotation depends linearly on the magnetic field and complies with g=0.46±0.02, i.e. the electronic g-factor.

Abstract: Optical and magneto-optical properties of In(Ga)MnAs layers fabricated by laser ablation on GaAs(100) substrates were studied. Spectra of the optical constants and the transversal Kerr effect (TKE) depended substantially on the conditions of layer fabrication and testified to the presence of MnAs inclusions in all the samples. The cross-sectional transmission electron microscopy revealed the presence in the layers of inclusions 10-40 nm in size. At room temperature, a strong resonant band was observed in the TKE spectra of some In(Ga)MnAs layers in the energy range 0.5-2.7 eV. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the semiconductor host.

Abstract: The phenomenal growths of information technology and related fields have warranted the development of new class of materials. Multifunctional oxides, magnetic-semiconductors, multiferroics and smart materials are just a few examples of such materials. They are needed for the development of novel technologies such as spintronics, magneto-electronics, radhard electronics, and advanced microelectronics. For these technologies, of particular interest are some solid solutions of ilmenite-hematite (IH) represented by (1-x) FeTiO3.xFe2O3 where x varies from 0 to 1; Mn-doped ilmenite (Mn+3-FeTiO3) and Mn-doped pseudobrookite, Mn+3-Fe2TiO5 (PsB). These multifunctional oxides are ferromagnetic with the magnetic Curie points well above the room temperature as well as wide bandgap semiconductors with band gap Eg > 2.5 eV. This paper outlines: (a) processing of device quality samples for structural, electrical and magnetic characterization, (b) fabrication and evaluation of an integrated structure for controlled magnetic switching, and (c) the response of the two terminal non-linear current-voltage (I-V) characteristics when biased by a dc voltage. Subsequently, we will identify a few microelectronic applications based on this class of oxides.

Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01, 0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors. Thermal treatment procedure was carried out in air at different temperatures in the range 400 - 900°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.

Abstract: Well-crystallized Fe1.18Ti0.82O3 and Fe1.18Ti0.82O3/Fe2O3 bilayered films were successfully prepared by using reactive helicon plasma sputtering technique. The solid solution films, Fe2−xTixO3, between hematite (α-Fe2O3) and ilmenite (FeTiO3) with various Ti concentrations, x, were epitaxially formed on the α-Al2O3(0001) single-crystalline substrates. The magnetic and electric properties of the solid solution films were systematically changed with increasing the Ti concentration. The film with the intermediate composition of Fe1.18Ti0.82O3 had the largest saturation magnetization at low temperature. However, the TC of solid solution films was linearly decreased with increasing the Ti concentration. The Fe1.18Ti0.82O3 film without Fe2O3 layers showed lower TC of about 200 K, while the TC of the Fe1.18Ti0.82O3/Fe2O3 bilayered film increased to about 220 K. The strong magnetic coupling between layers seemed to increase the TC of the attached Fe1.18Ti0.82O3 layer. The sharp interface between Fe1.18Ti0.82O3 and α-Fe2O3 layers was confirmed by the XPS depth profiling.

Abstract: We report on the effect of the oxygen partial pressure ratio in the sputtering gas mixture on the electrical and magnetic properties of cubic spinel ZnCo₂O₄ thin films grown by reactive magnetron sputtering. The conduction type and carrier concentration in ZnCo₂O₄ films were found to be dependent on the oxygen partial pressure ratio. The maximum electron and hole concentration at 300 K were estimated to be as high as 1.37 × 1020 cm^-3 and 2.81 × 10²⁰ cm^-3, respectively. While an antiferromagnetic coupling was found for n-type ZnCo₂O₄, a ferromagnetic interaction was observable in p-type ZnCo₂O₄, indicating hole-induced ferromagnetic transition in spinel ZnCo₂O₄.