Giant Magneto Impedance
Microwave Frequency Giant Magneto-Impedance (GMI) Structures for Miniaturized Magnetic Sensing and Magnetically Controlled Devices
Tech Area / Field
8 Project completed
Senior Project Manager
Komarkov D A
IVTAN (High Temperatures) / Scientific Center for Applied Problems in Electrodynamics, Russia, Moscow
- University of California / Center for Magnetic Recording Research, USA, CA, San Diego\nICMAT / Magnatic Materials Group, Italy, Rome\nAllied Signal Chemicals Inc. / Amorphous Metals, USA, NJ, Morristown\nInstitute for Applied Magnetism / Salvador Velayos Laboratory, Spain, Madrid\nUniversity of Plymouth / School of Electronics, Communication and Electrical Engineering, UK, Devonshire, Plymouth
Project summaryThe goals of the proposal are:
a) to develop physical understanding of the GMI effect in thin film multilayer structures.
b) to study static and high frequency magnetic properties of submicron GMI structures in order to come up with a technology enabling to produce sensors with certain magneto-impedance properties.
c) to develop methods of fabrication and incorporation of multilayer GMI structures into electronic circuits of miniature magnetic sensors and microwave tunable devices.
A recent discovery of the Giant Magneto- Impedance (GMI) effect in magnetic amorphous wires with a slightly negative magnetostriction has given rise to a new direction in the magnetic sensor technology. Conventional magnetoresistive materials (for high accuracy magnetic sensing and magnetic recording) exhibit sensitivity and thermal stability considerably lower than those of the GMI materials. Moreover, the GMI has been found also in the multilayer film structures comprising a highly conductive layer sandwiched between two ferromagnetic ones. The GMI multilayered structures seem to be promising for nanotechnologies - an attractive option for designers of magnetic sensors and heads. Fabrication of the GMI film stacks is based upon using magnetron or ion-beam sputtering, or e- beam evaporation in conjunction with a photolithographic procedure followed by a vacuum thermal annealing under an external magnetic field.
The GMI multilayer structures allow to considerably increasing the number of the GMI applications. Investigations carried out at the SCAPE have shown that the GMI effect remains considerably high over a frequency range up to a few GHz. It indicates that the new GMI structures can satisfy requirements imposed on high-speed magnetic heads working at a frequency of a few hundred megahertz. To satisfy such a high reproducing speed one has to maintain at least 1 GHz carrier frequency, which is far below the upper frequency limit where the GMI ceases to exist.
Potential applications of the GMI structures
The most promising applications the GMI elements can find in non-destructive control and magnetic sensing technology. A further miniaturization, increase of carrier frequency, sensitivity and thermal stability of the sensors put forward new requirements for the GMI materials. The GMI structure proposed here meets all these requirements and surpasses the materials known earlier. For example, widely used magnetoresistive sensors have the limited sensitivity of 2 % per Oe, temperature instability and a hysteresis. The sensitivity of the GMI structure proposed here can reach 100 % /Oe, the structure itself is thermally stable and exhibits no magnetic hysteresis.
Magnetic properties of the GMI structures are described in general by a non-reciprocal permeability tensor highly sensitive to external magnetic field which allows to use them in microwave tunable devices for portable wireless communication and aircraft radars. Attentuators, shifters, modulators etc. – where a highly energetic microwave flux is controlled by a low driving magnetic field - is a list of such devices. Well-known materials for such applications are high-frequency ferrites. They possess a high anisotropy and a high saturation field resulting in a low sensitivity. Furthermore, their fabrication in the form of a single crystal implies expansive and complicated technique. The GMI structures proposed here have advanages over the ferrites in sensitivity, response speed and manufacturability: using a low cost technology they can be easily incorporated into a microsized strip-line chip.
Main stages and expected results:
1 year: A program simulating the GMI structures with optimum geometry and ac magneto-transport properties to satisfy the required sensing and microwave applications will be developed. A testing setup enabling to study the GMI properties over a wide range of the electric current frequencies and external magnetic fields will be constructed. A GMI sandwich having thickness of less than 0.1 micron and width of 1-100 microns with the value of impedance change of up to 100% for magnetic fields of less than 10 Oe and the frequency range of 0.5- 5000 MHz will be fabricated. The magnetic layer composition is supposed to be (FeCo)x(CrNbSiBCuLeg)1-x, where Leg stands for additives facilitating the formation of a fine nanocrystalline structure. As a low resistively layer Cu, Ag or Al will be used.
Anticipated results: Multilayered structures with desirable GMI properties and low reversal fields will be obtained.
2 year: A technology allowing fabricating GMI structures, to modify their properties and to incorporate them into miniature sensing and microwave devices will be developed. The devices will be tested over a frequency range of 0.5 - 5000 MHz. Performance of the devices at different temperatures will be studied as well.
The GMI structures incorporated into sensing and microwave devices having sensitivity of not less than 10% / Oe within working frequency range of up to 200 MHz and temperature stability of about 0.05 FS / °C will be obtained.
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