We present experimental results of unprecedented large magnetoresistance obtained in stable electrodeposited Ni–Ni nanocontacts 10–30 nm in diameter. The contacts exhibit magnetoresistance of up to 700% at room temperature and low applied fields and, therefore, act as very effective spin filters. These large values of the magnetoresistance are attributed to spin ballistic transport through a magnetic “dead layer” at the contact of width of about 1 nm or smaller. Nanometer sized, high sensitive magnetoresistive sensors could become key elements for magnetic storage in the terabit/in.2 range and in high density magnetic random access memories.

The structure of wurtzite and zinc blende InAs–GaAs (001) core–shell nanowires grown by molecular beam epitaxy on GaAs (001) substrates has been investigated by transmission electron microscopy. Heterowires with InAs core radii exceeding 11 nm, strain relax through the generation of misfit dislocations, given a GaAs shell thickness greater than 2.5 nm. Strain relaxation is larger in radial directions than axial, particularly for shell thicknesses greater than 5.0 nm, consistent with molecular statics calculations that predict a large shear stress concentration at each interface corner.

Space-charge-limited current is often observed in semiconductor nanowires due to carrier depletion and reduced electrostatic screening. We present a numerical study on geometric scaling of the space-charge-limited current in nanowires, in comparison with the thin film and bulk geometries, using an n+-n-n+-model. The model highlights the effects of the surroundings for thin films and nanowires and shows that the dielectric properties of the semiconductor have a negligible effect on the space-charge-limited transport for small dimensions. The distribution of equilibrium and injected charge concentration vary as the semiconductor dimensionality is reduced. For low doping, the ohmic current is controlled by charge diffusion from degenerate contacts rather than by the nanowire impurity concentration. The results of numerical calculations agree with a simple capacitance formalism which assumes a uniform charge distribution along the nanowire, and experimental measurements for InAs nanowires confirm these results. The numerical model also predicts that an asymmetric nanowire contact geometry can enhance or limit charge injection.

Our results prove the local origin of magnetoresistance in electrochemically deposited Ni nanocontacts. Experiments have been done using a complex setup for both in situ growth and ballistic magnetoresistance ͑BMR͒ measurements. Nanocontacts have been grown between two macroscopic Ni wires. In situ experiments with variation of the nanocontact diameter from 3 to 20 nm have been done using the same pair of wires. BMR values from 0.5% to 100% have been observed but no correlation of BMR value with the sample resistance, i.e., with the nanocontact cross section, has been found. These results show that the BMR in the nanometric size contact is determined by local geometrical and magnetic structures near the nanocontact rather than by the contact cross section itself. The hypothesis of existence of the intrinsic nonmagnetic dead layer in the ferromagnetic nanocontact is proposed to account for the BMR properties of the nanometric size contacts. Additionally, we report a BMR value of 200% in a Ni nanocontact ͑5 nm diameter͒ electrochemically grown between two nonmagnetic macroscopic gold wires. An external magnetic field has been used during the electrochemical deposition to fix the easy magnetic axis of the deposited Ni layer.Ballistic magnetoresistance ͑BMR͒ in ferromagnetic atomic size ͑less than 1 nm diameter͒ nanocontacts were first reported in 1999. 1 The physical origin of the large magnetoresistance ͑MR͒ values ͑up to 300% at room temperatures͒ is a modification of the spin-dependent transparency of the nanocontact by the external magnetic field that changes the orientation of magnetization in an area of a few nanometers near the contact. 2 The BMR is a local effect, i.e., local magnetization near the contact plays the dominant role. Atomic size contacts are stable for a few minutes only, which impairs technological applications. Subsequent investigations have shown very large BMR ͑up to 700%͒ at room temperatures for nanometric size ͑1-100 nm diameter͒ contacts. 3,4 These nanocontacts were electrochemically grown between two ferromagnetic wires and they are stable for days. Stable BMR structures can successfully compete with giant MR 5 and tunnel MR 6 structures for applications as local magnetic sensors or as reading magnetic heads. An important question, which is very significant for practical applications, is the role of the bulk ferromagnetic electrodes. The use of large ferromagnetic electrodes ͑5 mm long and 0.

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