Switching Current vs. Magnetoresistance in Magnetic Multilayer Nanopillars

We study current-driven magnetization switching in nanofabricated magnetic trilayers, varying the magnetoresistance in three different ways. First, we insert a strongly spin-scattering layer between the magnetic trilayer and one of the electrodes, giving increased magnetoresistance. Second, we insert a spacer with a short spin-diffusion length between the magnetic layers, decreasing the magnetoresistance. Third, we vary the angle between layer magnetizations. In all cases, we find an approximately linear dependence between magnetoresistance and inverse switching current. We give a qualitative explanation for the observed behaviors, and suggest some ways in which the switching currents may be reduced.Comment: 3 pages, 4 figure

Current-Driven Magnetic Excitations in Permalloy-Based Multilayer Nanopillars

We study current-driven magnetization switching in nanofabricated Ni84Fe16/Cu/Ni84Fe16 trilayers at 295 K and 4.2 K. The shape of the hysteretic switching diagram at low magnetic field changes from 295 K to 4.2 K. The reversible behavior at higher field involves two phenomena, a threshold current for magnetic excitations closely correlated with the switching current, and a peak in differential resistance characterized by telegraph noise, with average period that decreases exponentially with current and shifts with temperature. We interpret both static and dynamic results at 295 K and 4.2 K in terms of thermal activation over a potential barrier, with a current dependent effective magnetic temperature.Comment: 4 pages, 4 Figure

Manipulating Current-Induced Magnetization Switching

We summarize our recent findings on how current-driven magnetization switching and magnetoresistance in nanofabricated magnetic multilayers are affected by varying the spin-scattering properties of the non-magnetic spacers, the relative orientations of the magnetic layers, and spin-dependent scattering properties of the interfaces and the bulk of the magnetic layers. We show how our data are explained in terms of current-dependent effective magnetic temperature.Comment: 6 pages, 6 figures, submitted to MMM'04 proceeding

crisscrossing Science Episode 042: Super Cold Computers for a Super Cool Future

In this episode, Chris Gaiser (professor of biology at Linfield College) and Mike Crosser (professor of physics at Linfield College) sit down with Norman Birge, a professor of physics from Michigan State University. Dr. Birge discusses his research into building computers with superconducting components. He has demonstrated, in principle, that these types of computers could be much more efficient than traditional computers because superconducting components will not generate heat. A lot of energy is used for computers currently in order to keep them from overheating during use (for instance, this is why your laptop has a built-in fan). A superconducting computer may solve this issue

Trade credit, risk sharing, and inventory financing portfolios

As an integrated part of a supply contract, trade credit has intrinsic connections with supply chain coordination and inventory management. Using a model that explicitly captures the interaction of firms' operations decisions, financial constraints, and multiple financing channels (bank loans and trade credit), this paper attempts to better understand the risk-sharing role of trade credit - that is, how trade credit enhances supply chain efficiency by allowing the retailer to partially share the demand risk with the supplier. Within this role, in equilibrium, trade credit is an indispensable external source for inventory financing, even when the supplier is at a disadvantageous position in managing default relative to a bank. Specifically, the equilibrium trade credit contract is net terms when the retailer's financial status is relatively strong. Accordingly, trade credit is the only external source that the retailer uses to finance inventory. By contrast, if the retailer's cash level is low, the supplier offers two-part terms, inducing the retailer to finance inventory with a portfolio of trade credit and bank loans. Further, a deeper early-payment discount is offered when the supplier is relatively less efficient in recovering defaulted trade credit, or the retailer has stronger market power. Trade credit allows the supplier to take advantage of the retailer's financial weakness, yet it may also benefit both parties when the retailer's cash is reasonably high. Finally, using a sample of firm-level data on retailers, we empirically observe the inventory financing pattern that is consistent with what our model predicts

Trade credit in supply chains: multiple creditors and priority rules

Priority rules determine the order of repayment to different creditors when the debtor cannot repay all of his debt. In this chapter, we study how different priority rules influence trade credit usage and supply chain efficiency under the risk-sharing role of trade credit. We find that with only demand risk, when the wholesale price is exogenous, trade credit with high priority can lead to high chain efficiency, yet trade credit with low priority allows more retailers to obtain trade credit and suppliers to gain higher profits. When the supplier has control of wholesale price, however, the supplier should extend unlimited trade credit, deeming priority rules irrelevant. When other non-demand risks, especially those with longer terms in nature, are present, we show several scenarios when the optimal trade credit policy should change according to different risks, and that in general, trade credit with low priority results in higher chain efficiency

Aspects of Discrete Breathers and New Directions

We describe results concerning the existence proofs of Discrete Breathers (DBs) in the two classes of dynamical systems with optical linear phonons and with acoustic linear phonons. A standard approach is by continuation of DBs from an anticontinuous limit. A new approach, which is purely variational, is presented. We also review some numerical results on intraband DBs in random nonlinear systems. Some non-conventional physical applications of DBs are suggested. One of them is understanding slow relaxation properties of glassy materials. Another one concerns energy focusing and transport in biomolecules by targeted energy transfer of DBs. A similar theory could be used for describing targeted charge transfer of nonlinear electrons (polarons) and, more generally, for targeted transfer of several excitations (e.g. Davydov soliton).Comment: to appear in the Proceedings of NATO Advanced Research Workshop "Nonlinearity and Disorder: Theory and Applications", Tashkent,Uzbekistan,October 1-6, 200

Universal conductance fluctuations in three dimensional metallic single crystals of Si

In this paper we report the measurement of conductance fluctuations in single crystals of Si made metallic by heavy doping (n \approx 2-2.5n_c, n_c being critical composition at Metal-Insulator transition). Since all dimensions (L) of the samples are much larger than the electron phase coherent length L_\phi (L/L_\phi \sim 10^3), our system is truly three dimensional. Temperature and magnetic field dependence of noise strongly indicate the universal conductance fluctuations (UCF) as predominant source of the observed magnitude of noise. Conductance fluctuations within a single phase coherent region of L_\phi^3 was found to be saturated at \approx (e^2/h)^2. An accurate knowledge of the level of disorder, enables us to calculate the change in conductance \delta G_1 due to movement of a single scatterer as \delta G_1 \sim e^2/h, which is \sim 2 orders of magnitude higher than its theoretically expected value in 3D systems.Comment: Text revised version. 4 eps figs unchange