A superconducting point contact is used to determine the spin polarization at the Fermi energy of several metals. Because the process of supercurrent conversion at a superconductor-metal interface (Andreev reflection) is limited by the minority spin population near the Fermi surface, the differential conductance of the point contact can reveal the spin polarization of the metal. This technique has been applied to a variety of metals where the spin polarization ranges from 35 to 90 percent: Ni0.8Fe0.2, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2.

Andreev reflection at a Pb/CrO(2) point contact has been used to determine the spin polarization of single-crystal CrO(2) films made by chemical vapor deposition. The spin polarization is found to be 0.96 +/- 0.01, which confirms that CrO(2) is a half-metallic ferromagnet, as theoretically predicted.

We have developed a simple method to measure the transport spin polarization of ferromagnetic materials. This technique relies on the fact that the Andreev reflection process at the interface between a superconductive and normal is influenced by the spin polarization P of the normal metal. In a very short time we have been able to measure the spin polarization of several metals: NixFe1−x, Ni, Co, Fe, NiMnSb, La0.7Sr0.3MnO3, and CrO2, whose spin polarization ranges from 35% to 90%. Our results compare well with other methods for measuring P.

Issues related to ''charge-spin coupling'' and the diffusive transport of nonequilibrium spin polarized electrons in nonmagnetic materials and at the interface between ferromagnetic and nonmagnetic materials are discussed theoretically. Equations that govern charge and spin transport in three dimensions are derived and appropriate boundary conditions are discussed. These results are applied to a numerical calculation of spin accumulation and diffusion in a two-dimensional Van der Pauw cross. A detailed model of spin transport at ferromagnetic-nonmagnetic metal interfaces is reviewed, the limiting cases of high and low interface conductance are treated, and the relevance of ''resistance mismatch'' for a variety of experimental systems is analyzed.Two fundamental properties reside with each conduction electron, the unit charge e and the unit magnetic moment B , the Bohr magneton, which is related to the quantum mechanical spin S by B ϭϪ(eប/mc)S, with m the electron mass and c the speed of light. The emerging field of Spintronics ͑Ref. 1͒ relies on ''charge-spin coupling:'' 2 characteristics of charge transport, such as voltage or current, can be modulated in a device structure by manipulating the spin, introducing new control parameters such as magnetic field, or new material properties such as magnetization. Distinct charge-spin coupling effects exist inside bulk materials and also at the interface between a ferromagnetic ͑F͒ and nonmagnetic ͑N͒ material.In a continuous ͑bulk͒ nonmagnetic system, the chargespin coupling that resides with individual electrons leads to the intuition that charge and spin are closely coupled for populations of carriers. This intuition is falsely reinforced by simple one-dimensional transport models where charge and spin flow along the same path. 3 For an ensemble of particles, in fact, the coupling is statistical and is generally weak. There are many possible spin distributions for any single charge distribution. Yet because of the statistics of large populations, the coupling of charge and spin results in substantial effects that can be used for device modulation.Boundary conditions for charge and spin transport are intrinsically different. 4 The electron charge is quantized and never changes, so that total charge is conserved in any conducting sample. By contrast, although electron spin is quantized, spin transport effects are based on spin orientation, a dynamic property. Spin orientation is not conserved in any sample, and the average orientation of a spin population is a continuous variable. Thus, ordinary electrodes on a conducting sample act as both sources and sinks for charge current. A ferromagnetic electrode can act as a source for spinpolarized current, but the sink for spin orientation is random, isotropic spin relaxation. 5 At a ferromagnet/nonmagnetic ͑F-N͒ material interface, the diffusion of polarized spins on both sides of the interface alters charge flow. Electronic interface properties such as resistance are changed, and the net transport of spin across the interfa...

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Articles you may be interested inSpherical cluster ensembles with fractal structure in LaSrMnO: New form of self-organization in solids Interplay of lattice strain and spin-polarization in ferromagnetic-insulator-ferromagnetic thin films: La 0.7 Ca 0.3 MnO 3 / LaAlO 3 / La 0.7 Sr 0.3 MnO 3A new method for determining the transport spin polarization, point contact tunneling from a low temperature superconductor into a ferromagnet, is used to determine the spin polarization of several LaSrMnO thin films and crystals. The Andreev process and its utility in measurements of spin-polarization are described. Preliminary results for the spin polarization of LSMO are presented.

A spin polarized current has been injected into high Tc superconductors resulting in a significant reduction in the superconductor’s critical current. Such injection may serve as the basis of a new class of superconducting devices for control, switching and amplification. Preliminary results using both Permalloy and CMR materials as injectors are presented.

Inorganic chemistryInorganic chemistry Z 0100 Charge and Spin Diffusion in Mesoscopic Metal Wires and at Ferromagnet/Nonmagnet Interfaces -[30 refs.]. -(JOHNSON, M.; BYERS, J.; Phys. Rev. B: Condens. Matter Mater. Phys. 67 (2003) 12, 112/1-112/7; Nav. Res. Lab., Washington, DC 20375, USA; Eng.) -Lindner 38-218