New Materials for High-sensitive Magnetoresistive Sensors with Wide Field of Application
Tech Area / Field
- INS-DET/Detection Devices/Instrumentation
8 Project completed
Senior Project Manager
Mitina L M
TsNIIChermet (Ferrous Metallurgy), Russia, Moscow
- Laboratoire de Science et Genie des Materiaux Metalliques, France, Nancy\nRoyal Institute of Technology / Institute of Physics, Sweden, Stockholm
Project summaryBasing on the experience of project participants in the field of military industry problems, particularly in creating of aiming, tracing and navigation systems, also the systems for identifying of moving objects, the task was stated to design the new class of ferromagnetic magnetoresistive materials with the magneto-resistance ratio higher than 8-10% at room temperature and magnetic field less than 10 ml. These materials make possible the creating of devices with extensive field of application and which will be beyond of competition in comparing with the existing similar devices. The comparison of the performance characteristics of sensors based on various principles shows that output signal of ferromagnetic sensors at room temperature and weak magnetic fields (Ј 50 mT) is many times higher than output level of semiconductor and Hail-effect magnitoresistors. However, there are problems in the field of magnetoresistive media (MRM) for sensors production. The project aim is in overcoming the said hrobiems.
At present, main candidate materials for MRM are the materials exhibiting the so called giant magnetoresistive effect (GMR-effect). The said effect achieves the value from 5 up to 100% at low temperatures and high magnetic fields. Among these materials the multilayered films (artificial modulated structures), granular-alloy films (with magnetic nanometric inclusions in nonmagnetic media), compounds with intrinsic GMR, and alloys with natural modulated structures. In the last case the dispersion of magnetic particles in nonmagnetic media achieved during the solid solution decomposition without layer-by-layer epithaxy growth (such as in the multilayered films) or coupled sputter deposition (such as in the granular films). In multilayered arid granular films and in chemical compounds with intrinsic GMR the largest value of QMR was achieved in high magnetic fields of the order 1 T and at low temperatures (4,2-77 K). Besides, the formation of MRM on the base of multilayered and granular structures are connected with the complex technology of the molecular beam epithaxy, ultra high vacuum, layer-by-layer sputtering from independent targets etc. MRM with the artificial modulated structures have a nonlinear (bell-shaped) raagnetoresistance characteristic and negative temperature coefficient of GMR.
Among the known variants of MRM fabrication the MRM with the natural modulated structures are most worthwhile from the technical and commercial point of view. The advantages of this variant in comparison with the best MRM-specomens are: more extensive range of magnetic field with linear GMR-characteristic; positive temperature coefficient of GMR as contrast with the negative temperature coefficient of artificial modulated structures; the very principle of natural modulated structure formation makes possible the applicability of ordinary methods of melt quenching, film sputtering and heat treatment, i.e. the using of relatively simple technology and industrial equipment.
At the same time, MRM with natural modulated structures have been investigated in very small degree. Relatively low MR ratio at low fields in the MRM with the natural modulated structures which was achieved up to now (alloys of Cunife type, 6.5% at 6000 ml) can be attributed to nonoptimal alloy composition. We have a know-how in the alloy composition and heat treatment regimes ensuring the achievement of natural modulated structure with large GMR-effect. In accordance with know-how one can to select such a combination of transition 3d- and 4f-metais that will provide obtaining zero values of magnetic anisotropy 琿■magnetostriction constants. Thus, magnetization process will be developed at low magnetic fields.
Adding the metalloid elements from III-V groups of Periodical system, there will be conditions for solid solution decomposition on the constituents with different kinds and magnitude of magnetic exchange interaction. So, it will give rise for GMR-effect such as in multilayered films. Zero values of anisotropy and magnetostriction constants (see above) will guarantee the appearance
the GMR in low field. In the course of project accomplishing we will develop MRM with the natural modulated structure and method of preparation for said media with the GMR-values of 8-10% in the fields of the order 10 ml.
The project objectives will be achieved with the using of melt quenching, high-frequency sputtering of thin films, heat treatment in magnetic field. Fine structure and magnetic structure of the alloys and films will be investigated by the transmission electron microscopy and X-rays diffraction, calorimetry, magnetic analysis, ferromagnetic resonance, magnetooptical Kerr-effect. Sensor designing and fabrication will be accomplished with the use of electron lithography and chemical etching. New sensors will be used for designing and fabrication of pilot specimens of following devices:
- a defectoscope for nondestructive testing of hidden defects in articles from magnetic and nonmagnetic materials (airframes, casing of ships, tube walls, autoclaves, tanks for chemically active substances etc.);
- devices for control of actual metal condition in the dangerous sites of structural parts of complex apparatus (nuclear energetic, plane and rocket industry, magistral pipelines etc);
- devices for measurement of rotary speed of motor of, videorecording unit and phase position of recording head rotor of videorecording unit;
- devices for measurement of the coating thickness from 5 to 1500 m, on the ferromagnetic substrate.
It will be possible the scientific 'collaboration with Prof. M.Muller from Technical University of Dresden (Germany) in the field of structural transitions in magnetic alloys.
1) Prof. M.Muller-Technical university of Dresden, Department of Maschine Building, Helmolltzstrasse 7, Berndt-Bau, D-01062 Dresden, Germany.
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