Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1995-06-19
1997-09-16
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetometers
338 32R, G01R 3306, G01R 3309
Patent
active
056684738
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistive sensor. More particularly, the present invention relates to a magnetoresistive sensor including a layer system having a measuring layer, a bias layer, and an interlayer, and including measuring contacts on the layer system.
In ferromagnetic transition metals such as nickel (Ni), iron (Fe) or cobalt (Co), and in alloys containing these metals, the electrical resistance depends on the magnitude and direction of a magnetic field permeating the material. This effect is referred to as anisotropic magnetoresistance (AMR) or anisotropic magnetoresistive effect. This is physically based on the different scattering cross sections of electrons having different spins which correspondingly are referred to as majority electrons and minority electrons of the D band. A thin layer made of such a magnetoresistive material having a magnetization in the plane of the layer is generally used for magnetoresistive sensors. The change in resistance as the magnetization rotates with respect to the direction of the current may amount to several percent of the normal isotropic resistance.
Multilayer systems are known which comprise a plurality of ferromagnetic layers which are arranged in a stack and are separated from one another by metallic interlayers, and whose magnetizations in each case coincide with the plane of the layer. The respective layer thicknesses in this arrangement are chosen to be considerably smaller than the mean free path of the conduction electrons. In such layer systems there then arises, in the individual layers, in addition to the anisotropic magnetoresistive effect, the so-called giant magnetoresistive effect or giant magnetoresistance (Giant MR), which is due to the differential scattering of majority and minority conduction electrons in the bulk of the layers, especially in alloys, and at the interfaces between the ferromagnetic layers and the interlayers. This Giant MR is an isotropic effect and may be considerably larger than the anisotropic MR, with values of up to 70% of the normal isotropic resistance.
Two basic types of such Giant-MR multilayer systems are known. In the first type, the ferromagnetic layers are antiferromagnetically coupled to one another via the interlayers, so that those magnetizations of two adjacent ferromagnetic layers, which coincide with the planes of the layers, align themselves antiparallel with respect to one another in the absence of an external magnetic field. An example of this type of Giant-MR multilayer systems are iron-chromium superlattices (Fe--Cr superlattices) having ferromagnetic layers consisting of Fe and antiferromagnetic interlayers consisting of Cr. An external magnetic field causes the magnetizations of adjacent ferromagnetic layers to rotate against the antiferromagnetic coupling forces and to align themselves in parallel. This reorientation of the magnetizations by the magnetic field results in a steady decrease of the Giant MR, which decrease is a measure for the magnitude of the magnetic field. Once a saturation field strength H.sub.S is reached, no further change in the Giant MR takes place, because all magnetizations are then aligned in parallel with respect to one another. The Giant MR in this situation depends solely on the magnitude of the field strength ("Physical Review Letters", Vol. 61, No. 21, Nov. 21st 1988, pages 2472-2475).
This type of Giant-MR multilayer system comprising antiferromagnetically coupled ferromagnetic layers has also been the subject of theoretical calculations which show that the current coefficients and the transmission coefficients for spin-up electrons scattered at the interfaces and similar spin-down electrons depend on the angle between the magnetizations in adjacent ferromagnetic layers. According to these calculations, the Giant MR increases steadily as the angle between the two magnetizations increases from 0.degree. to 180.degree., and is greatest at an angle of 180.degree. ("Physical Review Letters", Vol. 63, No. 6, August 1989, pages
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Strecker Gerard R.
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