A spin metal-oxide-semiconductor field-effect transistor using half-metallic-ferromagnet contacts for the source and drain

We propose and theoretically analyze a novel metal-oxide-semiconductor field-effect-transistor (MOSFET) type of spin transistor (hereafter referred to as a spin MOSFET) consisting of a MOS gate structure and half-metallic-ferromagnet (HMF) contacts for the source and drain. When the magnetization configuration between the HMF source and drain is parallel (antiparallel), highly spin-polarized carriers injected from the HMF source to the channel are transported into (blocked by) the HMF drain, resulting in the magnetization-configuration-dependent output characteristics. Our two-dimensional numerical analysis indicates that the spin MOSFET exhibits high (low) current drive capability in the parallel (antiparallel) magnetization, and that extremely large magnetocurrent ratios can be obtained. Furthermore, the spin MOSFET satisfies other important requirements for "spintronic" integrated circuits, such as high amplification capability, low power-delay product, and low off-current.Comment: 5 pages, 3 figure

Magneto-optical properties of a new group-IV ferromagnetic semiconductor Ge1-xFex grown by low-temperature molecular beam epitaxy

A new group-IV ferromagnetic semiconductor, Ge1-xFex, was successfully grown by low-temperature molecular beam epitaxy (LT-MBE) without precipitation of ferromagnetic Ge-Fe intermetallic compounds. The ferromagnetism of Ge1-xFex films was investigated by magnetic circular dichroism (MCD). In particular, the influence of the Fe content (FFe/FGe =1 - 10%) and growth temperature (100, 200OC) on the ferromagnetism was carefully studied. The MCD measurements revealed that the band structure of the Ge1-xFex films was identical with that of bulk Ge, and that the large spin splitting of the band structure was induced by the incorporation of Fe atoms into the Ge matrix, indicating the existence of s,p-d exchange interactions. The Ge1-xFex films showed ferromagnetic behavior and the ferromagnetic transition temperature linearly increased with increasing the Fe composition. These results indicate that the epitaxially grown Ge1-xFex is an intrinsic ferromagnetic semiconductor.Comment: 15 pages, 4 figures. to appear in J. Appl. Phy

On ‘Creative Cities’ governance models: a comparative approach

The implementation of ‘Creative Cities’ projects, all over the world, in recent years, has been characterized by a great diversity of institutional frameworks and governance mechanisms. Departing from the contemporary debates on “creative industries” and “creative cities”, this paper aims to discuss this diversity of regulatory mechanisms and governance forms. Some tentative typologies of case studies and governance mechanisms are drawn in order to improve the understanding of those dynamics, to build up knowledge on suitable ‘Creative Cities’ governance models, and to develop ideas to support a strategy for public intervention in the Portuguese case

Structure and magnetism of self-organized Ge(1-x)Mn(x) nano-columns

We report on the structural and magnetic properties of thin Ge(1-x)Mn(x)films grown by molecular beam epitaxy (MBE) on Ge(001) substrates at temperatures (Tg) ranging from 80deg C to 200deg C, with average Mn contents between 1 % and 11 %. Their crystalline structure, morphology and composition have been investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy and x-ray diffraction. In the whole range of growth temperatures and Mn concentrations, we observed the formation of manganese rich nanostructures embedded in a nearly pure germanium matrix. Growth temperature mostly determines the structural properties of Mn-rich nanostructures. For low growth temperatures (below 120deg C), we evidenced a two-dimensional spinodal decomposition resulting in the formation of vertical one-dimensional nanostructures (nanocolumns). Moreover we show in this paper the influence of growth parameters (Tg and Mn content) on this decomposition i.e. on nanocolumns size and density. For temperatures higher than 180deg C, we observed the formation of Ge3Mn5 clusters. For intermediate growth temperatures nanocolumns and nanoclusters coexist. Combining high resolution TEM and superconducting quantum interference device magnetometry, we could evidence at least four different magnetic phases in Ge(1-x)Mn(x) films: (i) paramagnetic diluted Mn atoms in the germanium matrix, (ii) superparamagnetic and ferromagnetic low-Tc nanocolumns (120 K 400 K) and (iv) Ge3Mn5 clusters.Comment: 10 pages 2 colonnes revTex formatte

Spin-glass-like behavior of Ge:Mn

We present a detailed study of the magnetic properties of low-temperature-molecular-beam-epitaxy grown Ge:Mn dilute magnetic semiconductor films. We find strong indications for a frozen state of Ge_{1-x}Mn_{x}, with freezing temperatures of T_f=12K and T_f=15K for samples with x=0.04 and x=0.2, respectively, determined from the difference between field-cooled and zero-field-cooled magnetization. For Ge_{0.96}Mn_{0.04}, ac susceptibility measurements show a peak around T_f, with the peak position T'_f shifting as a function of the driving frequency f by Delta T_f' / [T_f' Delta log f] ~ 0.06, whereas for sample Ge_{0.8}Mn_{0.2} a more complicated behavior is observed. Furthermore, both samples exhibit relaxation effects of the magnetization after switching the magnitude of the external magnetic field below T_f which are in qualitative agreement with the field- and zero-field-cooled magnetization measurements. These findings consistently show that Ge:Mn exhibits a frozen magnetic state at low temperatures and that it is not a conventional ferromagnet.Comment: Revised version contains extended interpretation of experimental dat

High Temperature Ferromagnetism in GaAs-based Heterostructures with Mn Delta Doping

We show that suitably-designed magnetic semiconductor heterostructures consisting of Mn delta-doped GaAs and p-type AlGaAs layers, in which the locally high concentration of magnetic moments of Mn atoms are controllably overlapped with the 2-dimensional hole gas wavefunction, realized remarkably high ferromagnetic transition temperatures (TC). Significant reduction of compensative Mn interstitials by varying the growth sequence of the structures followed by low temperature annealing led to high TC up to 250 K. The heterostructure with high TC exhibited peculiar anomalous Hall effect behavior, whose sign depends on temperature.Comment: 18 pages, 4 figure

Application of Weather Generation to High Frequency and High Resolution Gridded Datasets in Sao Paulo.

201