Electric readout of magnetization dynamics in a ferromagnet-semiconductor system

We apply an analysis of time-dependent spin-polarized current in a semiconductor channel at room temperature to establish how the magnetization configuration and dynamics of three ferromagnetic terminals, two of them biased and third connected to a capacitor, affect the currents and voltages. In a steady state, the voltage on the capacitor is related to spin accumulation in the channel. When the magnetization of one of the terminals is rotated, a transient current is triggered. This effect can be used for electrical detection of magnetization reversal dynamics of an electrode or for dynamical readout of the alignment of two magnetic contacts.Comment: Revised version, 8 pages, 3 figure

Spintronics for electrical measurement of light polarization

The helicity of a circularly polarized light beam may be determined by the spin direction of photo-excited electrons in a III-V semiconductor. We present a theoretical demonstration how the direction of the ensuing electron spin polarization may be determined by electrical means of two ferromagnet/semiconductor Schottky barriers. The proposed scheme allows for time-resolved detection of spin accumulation in small structures and may have a device application.Comment: Revised version, 8 two-column pages, 5 figures; Added: a comprehensive time dependent analysis, figures 3b-3c & 5, equations 6 & 13-16 and 3 references. submitted to Phys. Rev.

Spin and energy relaxation in germanium studied by spin-polarized direct-gap photoluminescence

Spin orientation of photoexcited carriers and their energy relaxation is investigated in bulk Ge by studying spin-polarized recombination across the direct band gap. The control over parameters such as doping and lattice temperature is shown to yield high polarization degree, namely larger than 40%, as well as a fine-tuning of the angular momentum of the emitted light with a complete reversal between right- and left-handed circular polarization. By combining the measurement of the optical polarization state of band-edge luminescence and Monte Carlo simulations of carrier dynamics, we show that these very rich and complex phenomena are the result of the electron thermalization and cooling in the multi-valley conduction band of Ge. The circular polarization of the direct-gap radiative recombination is indeed affected by energy relaxation of hot electrons via the X valleys and the Coulomb interaction with extrinsic carriers. Finally, thermal activation of unpolarized L valley electrons accounts for the luminescence depolarization in the high temperature regime

Indigenous Rangeland Management Practices and Resource Use Patterns by Agro-pastoralists in Nanton District, Ghana

Indigenous knowledge plays a pivotal role in the sustainable management of rangeland and the use of rangeland resources. The study was conducted with the main aim of identifying some indigenous rangeland and herd management strategies employed by agro-pastoralists in the area. Data were collected from 98 agro-pastoralists in 25 communities selected at random using structured questionnaires which contained a checklist of questions regarding indigenous rangeland and herd management practices. The study showed that the majority of the farmers (63%) practiced free grazing followed by rotational (31%) and zero-grazing (6%) systems. Majority of the farmers (77.6%) do not practice any form of herd management techniques. Whilst 12.2% practiced herd splitting, 10.2% confined their younger herds in enclosures during the rainy season where they are offered supplementary feeds. Among the factors responsible for rangeland degradation in the district were bush burning, deforestation, drought, and over-grazing. Traditional rangeland conservation practices adopted by farmers to conserve rangelands in the area were; early burning, no burning, and no felling of economic trees such as Adansonia digitata, Vitellaria paradoxa and Diospyros mespiliformis. Apart from the Fulani tribe who are pure pastoralists and do not necessarily have rights to own lands across the communities, all other farmers have unlimited access to other rangeland resources besides grazing their animals. These results suggest that a lot more effort and education are needed to enlighten farmers on the consequences of open grazing as majority of them are engaged in the practice.

Ariel - Volume 5 Number 3

Editor J.D. Kanofsky Entertainment Editors Robert Breckenridge Gary Kaskey Overseas Editor Mike Sinason Staff Ken Jaffe Bob Sklaroff Janet Weish David Jacoby Circulation Editor Jay Amsterdam Humorist Jim McCan

Reconfigurable nanoelectronics using graphene based spintronic logic gates

This paper presents a novel design concept for spintronic nanoelectronics that emphasizes a seamless integration of spin-based memory and logic circuits. The building blocks are magneto-logic gates based on a hybrid graphene/ferromagnet material system. We use network search engines as a technology demonstration vehicle and present a spin-based circuit design with smaller area, faster speed, and lower energy consumption than the state-of-the-art CMOS counterparts. This design can also be applied in applications such as data compression, coding and image recognition. In the proposed scheme, over 100 spin-based logic operations are carried out before any need for a spin-charge conversion. Consequently, supporting CMOS electronics requires little power consumption. The spintronic-CMOS integrated system can be implemented on a single 3-D chip. These nonvolatile logic circuits hold potential for a paradigm shift in computing applications.Comment: 14 pages (single column), 6 figure

Electrical expression of spin accumulation in ferromagnet/semiconductor structures

We treat the spin injection and extraction via a ferromagnetic metal/semiconductor Schottky barrier as a quantum scattering problem. This enables the theory to explain a number of phenomena involving spin-dependent current through the Schottky barrier, especially the counter-intuitive spin polarization direction in the semiconductor due to current extraction seen in recent experiments. A possible explanation of this phenomenon involves taking into account the spin-dependent inelastic scattering via the bound states in the interface region. The quantum-mechanical treatment of spin transport through the interface is coupled with the semiclassical description of transport in the adjoining media, in which we take into account the in-plane spin diffusion along the interface in the planar geometry used in experiments. The theory forms the basis of the calculation of spin-dependent current flow in multi-terminal systems, consisting of a semiconductor channel with many ferromagnetic contacts attached, in which the spin accumulation created by spin injection/extraction can be efficiently sensed by electrical means. A three-terminal system can be used as a magnetic memory cell with the bit of information encoded in the magnetization of one of the contacts. Using five terminals we construct a reprogrammable logic gate, in which the logic inputs and the functionality are encoded in magnetizations of the four terminals, while the current out of the fifth one gives a result of the operation.Comment: A review to appear in Mod. Phys. Lett.

Graphite and graphene as perfect spin filters

Based upon the observations (i) that their in-plane lattice constants match almost perfectly and (ii) that their electronic structures overlap in reciprocal space for one spin direction only, we predict perfect spin filtering for interfaces between graphite and (111) fcc or (0001) hcp Ni or Co. The spin filtering is quite insensitive to roughness and disorder. The formation of a chemical bond between graphite and the open $d$-shell transition metals that might complicate or even prevent spin injection into a single graphene sheet can be simply prevented by dusting Ni or Co with one or a few monolayers of Cu while still preserving the ideal spin injection property

Microsatellite gene diversity in coconut (Cocos nucifera L.) accessions resistants to lethal yellowing disease

One of the problems faced in coconut cultivation is the lethal yellowing disease. Experimental trials, conducted in endemic region, showed that the Vanuatu Tall and Sri-Lanka Green Dwarf genotypes weretolerant while the West African Tall appeared susceptible to the lethal yellowing disease. Genetic differences between these tolerant genotypes and the susceptible ones were evaluated using twelvemicrosatellite markers. This work aimed to use identified materials as reference to select suitable parents for gene mapping studies. A total of 58 alleles were detected at the 12 microsatellite loci. Thenumber of alleles varied from 3 to 7, with an average of 4.83 alleles. The Fst index revealed that 59.70% of the total allele variability explained differences between the three accessions. Genotypes of WestAfrican Tall, susceptible to the lethal yellowing disease, were less genetically clustered to the genotypes of the two tolerant accessions. This differentiation was based on specific alleles and frequency variation of shared allele in the three accessions. This molecular typology was useful as reference for large molecular screening of coconut genetic resources and the identification of suitableparents for the development of mapping populations for tagging the lethal yellowing resistance genes