Ni Gang

Hall Effect of (Co0.34Fe0.66)0.42(SiO2)0.58 Granular Films

The (Co0.34Fe0.66)0.42(SiO2)0.58 (volume fraction) granular films were fabricated by using the magnetron sputtering technique, and a saturated Hall resistivity ρxys of about 29 µΩcm was observed at room temperature, which was almost three orders of magnitude greater than that in the pure ferromagnetic sample. The measured linear dependence of resistivity ρxx versus log10T and magnetoresistance effect indicated that the the Co0.34Fe0.66 volume fraction in the films was near percolation threshold. The giant Hall effect in the (Co0.34Fe0.66)0.42(SiO2)0.58 granular film may originate from the percolation phenomenon.

Transport properties, microstructures and domain observation in Ag1-x-(Ni0.8Co0.2)x granular films

Abstract A series of Ag 1-x -(Ni 0.8 Co 0.2 ) x granular film samples were prepared by ion-beam cosputtering technique. Magnetoresistance was measured using conventional four terminal method at room temperature. A transition from giant magnetoresistance (GMR) to anisotropy magnetoresistance(AMR) has been observed in these samples as x rises, and the maximum of magnetoresistance ratio as large as −3% for x = 40 at .%. The VSM results of the samples show gradual changes from superparamagnetism to ferromagnetism as x increases. XRD, TEM and MFM were performed to investigate microstructures of these samples. The lined stripe domains have been observed in x = 75 at .% sample using MFM, but the domains gradually disappear as x decreases. It suggests that the transition from GMR to AMR result from enhanced interparticle interaction in the samples.

Dependence of tunnel resistance on the injection current of magnetic tunnel junctions

Anomalous transport behaviour, i.e. the dependence of the tunnel resistance on the injection current, has been discovered in Ta/Co/Al2O3/FeNi tunnel junctions. The zero-field voltage-current characteristic of the magnetic tunnelling junction obeys the transport principle of the normal tunnel junction at low injection current, but it exhibits a negative resistance behaviour when the injection current is raised to the break-over current level. The physics of the restorable electric breakdown has been initially studied.

Magnetization reversal mechanism of magnetic tunnel junctions

Using the ion-beam-sputtering technique, we have fabricated Fe/Al2O3/Fe magnetic tunnelling junctions (MTJs). We have observed double-peaked shapes of curves, which have a level summit and a symmetrical feature, showing the magnetoresistance of the junction as a function of applied field. We have measured the tunnel conductance of MTJs which have insulating layers of different thicknesses. We have studied the dependence of the magnetoresistance of MTJs on tunnel conductance. The microstructures of hard- and soft-magnetic layers and interfaces of ferromagnets and insulators were probed. Analysing the influence of MJT microstructures, including those having clusters or/and granules in magnetic and non-magnetic films, a magnetization reversal mechanism (MRM) is proposed, which suggests that the MRM of tunnelling junctions may be explained by using a group-by-group reversal model of magnetic moments of the mesoscopical particles. We discuss the influence of MTJ microstructures, including those with clusters or/and granules in the ferromagnetic and non-magnetic films, on the MRM.