Electrical Investigation of the Oblique Hanle Effect in Ferromagnet/Oxide/Semiconductor Contacts

We have investigated the electrical Hanle effect with magnetic fields applied at an oblique angle ({\theta}) to the spin direction (the oblique Hanle effect, OHE) in CoFe/MgO/semiconductor (SC) contacts by employing a three-terminal measurement scheme. The electrical oblique Hanle signals obtained in CoFe/MgO/Si and CoFe/MgO/Ge contacts show clearly different line shapes depending on the spin lifetime of the host SC. Notably, at moderate magnetic fields, the asymptotic values of the oblique Hanle signals (in both contacts) are consistently reduced by a factor of cos^2({\theta}) irrespective of the bias current and temperature. These results are in good agreement with predictions of the spin precession and relaxation model for the electrical oblique Hanle effect. At high magnetic fields where the magnetization of CoFe is significantly tilted from the film plane to the magnetic field direction, we find that the observed angular dependence of voltage signals in the CoFe/MgO/Si and CoFe/MgO/Ge contacts are well explained by the OHE, considering the misalignment angle between the external magnetic field and the magnetization of CoFe.Comment: 19 pages, 8 figure

Environmental Regulations in Private and Mixed Duopolies: Emission Taxes versus Green R&D Subsidies

In the presence of R&D spillovers, we compare environmental regulations between an emission taxes and green R&D subsidies in private and mixed duopoly markets. We show that the green R&D subsidy is better (worse) than the emission tax when the green R&D cost is low (high) irrespective of the R&D spillovers, whereas the existence of a public firm encourages the government to adopt the subsidy policy. We then show that the optimal policy choice depends on the level of the R&D cost and the degree of R&D spillovers. In particular, when the R&D cost is high and the spillover rate is (not) weak, the government should choose the emission tax and (not) privatize the public firm. However, when the R&D cost is low, such a privatization policy is not desirable to society irrespective of the R&D spillovers

Optimal Policy Combinations of Abatement Subsidy and Pollution Tax in Vertical Oligopolies

AbstractThis article investigates environmental regulations on eco-industry in vertical oligopolies, in which the upstream industry produces abatement goods reducing pollutants and the downstream industry produces consumption goods emitting pollutants. We devise the optimal combination of appropriate policy instruments and show that an optimal pollution tax should be used for the negative externality and output restrictions in final production, and an optimal abatement subsidy should incorporate the effect of upstream market restrictions on abatement activity. We also examine the welfare effect of the subsidy policy on the abatement technology in tax/subsidy combination