Experimental observation of switching in ferromagnetic nanoscale double disks

We investigated a system of two overlapping ferromagnetic permalloy disks, called a hysteron. For sufficiently small disk diameters the hysteron contains only one vortex which is displaced off the center of the disk hosting it. By swapping the vortex from one side of the disk to the other via an in-plane magnetic field, the magnetization in the appended disk is reversed. The magnetization reversal process based on these off-center magnetic vortex states was theoretically found to have low switching fields, as magnetization reversal does not require wall nucleation. Here we investigate hysterons experimentally by studying magnetization reversal and configuration by means of Lorentz transmission electron microscopy and electron holography. For the smallest hysterons with individual disk diameters below ${\approx}$200 nm we found the peculiar switching scheme suggested recently

Do Cooperatives Offer High Quality Products?

The present paper investigates the free-riding problem in determining product quality within cooperatives in a vertically related market. Whereas the individual member has to bear all costs associated with higher quality, the benefits of delivering higher quality have to be shared among all members. On the basis of a Mixed-Oligopoly model, we show that the free-rider problem in the supply of high-quality products, although important for the members of the cooperative, may not be strong enough to ensure that firms will always supply higher quality than cooperatives. Whether the cooperative can overcome the free-riding problem and supply a final product of high quality is shown to depend on the consumer's valuation of quality, the costs of producing high quality, the way in which the quality of the final product is determined from the quality levels of the inputs delivered as well as on the number of members of the cooperative.Agribusiness,

Product Quality in the Food Chain: Do Cooperatives Offer High Quality Products?

Cooperatives and investor-owned firms are alternative forms of business organisation that coexist and compete in many markets. The theoretical literature has identified a number of comparative advantages and disadvantages of cooperatives. Decentralized decision making within cooperatives may lead to quality coordination problems (free-riding on product quality), for example: whereas the individual member has to bear the full costs associated with higher quality, the benefits of delivering higher quality will be shared among all members. The present paper investigates this free-riding problem in determining product quality within a marketing cooperative in a vertically related market (food chain). On the basis of a mixed-oligopoly model, we show that the free-rider problem in the supply of high-quality products might be strong enough to ensure that cooperatives will never supply higher quality than investor-owned firms. Whether the cooperative can overcome the free-riding problem and supply a final product of high quality is shown to depend on the consumer’s valuation of quality, the costs of producing high quality, the way in which the quality of the final product is determined from the quality levels of the inputs delivered, the possibilities in controlling product quantity as well as on the number of members of the cooperative.product quality, cooperatives, food chain, competition, Agricultural and Food Policy, Food Consumption/Nutrition/Food Safety,

Local spin valve effect in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report on a local spin valve effect observed unambiguously in lateral all-semiconductor all-electrical spin injection devices, employing p+-(Ga,Mn)As/n+-GaAs Esaki diode structures as spin aligning contacts. We discuss the observed local spin-valve signal as a result of interplay between spin-transport-related contribution and tunneling anisotropic magnetoresistance of magnetic contacts. The magnitude of the spin-related magnetoresistance change is equal to 30 Ohm which is twice the magnitude of the measured non-local signal.Comment: submitted to Appl. Phys. Let

Tunneling Anisotropic Spin Polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices

We report here on anisotropy of spin polarization obtained in lateral all-semiconductor all-electrical spin injection devices, employing $p^{+}-$(Ga,Mn)As/$n^{+}-$GaAs Esaki diode structures as spin aligning contacts, resulting from the dependence of the efficiency of spin tunneling on the orientation of spins with respect to different crystallographic directions. We observed an in-plane anisotropy of $~8$ in case of spins oriented either along $[1\bar{1}0]$ or $[110]$ directions and $~25$ anisotropy between in-plane and perpendicular-to-plane orientation of spins.Comment: 9 pages, 3 figure

All-electrical measurements of direct spin Hall effect in GaAs with Esaki diode electrodes

We report on measurements of direct spin Hall effect in a lightly n-doped GaAs channel. As spin detecting contacts we employed highly efficient ferromagnetic Fe/(Ga,Mn)As/GaAs Esaki diode structures. We investigate bias and temperature dependence of the measured spin Hall signal and evaluate the value of total spin Hall conductivity and its dependence on channel conductivity and temperature. From the results we determine skew scattering and side jump contribution to the total spin hall conductivity and compare it with the results of experiments on higher conductive n-GaAs channels[Phys. Rev. Lett. 105,156602(2010)]. As a result we conclude that both skewness and side jump contribution cannot be fully independent on the conductivity of the channel.Comment: 14 pages, 4 figure

On the Relative Disadvantage of Cooperatives: Vertical Product Differentiation in a Mixed Oligopoly

We investigate the incentive to provide goods of high quality in a vertically related market for different types of business organizations, a farmer-owned cooperative and an investor-owned firm. Contrary to the firm, the cooperative is characterized by decentralized decision making, which gives rise to overproduction and problems coordinating the quality decisions of its members (free riding). Comparing both manufacturers acting as monopolists we show that the cooperative will never supply final goods of higher quality than the firm, and that the problem of quality coordination is mitigated if the cooperative succeeds in preventing overproduction. When a cooperative faces competition of an investor-owned firm (mixed duopoly), it will - except in one limit case - never produce final goods of a higher quality than the firm and will deliver lower quality in a number of scenarios

Density of States of GaAs-AlGaAs Heterostructures Deduced from Temperature Dependend Magnetocapacitance Measurements

Abstract We have analyzed the density of states of a two dimensional electron gas in a GaAs- AlGaAs hetereostructure by measuring the magnetocapacitance in magnetic fields up to 6 Tesla at temperatures below 10 K. The experimental data are well described by a Gaussian-like density of states where the linewidth à is proportional to B

Monte Carlo simulations reveal the straightening up of an end-grafted flexible chain with a rigid side chain

We have studied the conformational properties of a flexible end-grafted chain (length $N$) with a rigid side chain (length $S$) by means of Monte Carlo simulations. Depending on the lengths $N$ and $S$ and the branching site, $b$, we observe a considerable straightening of the flexible backbone as quantified via the gyration tensor. For $b=N$, i.e. when attaching the side chain to the free end of the flexible backbone, the effect was strongest