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Giant Magnetoimpedance Materials: Fundamentals and Applications Available online at www.sciencedirect.com Progress in Materials Science 53 (2008) 323–420 www.elsevier.com/locate/pmatsci Giant magnetoimpedance materials: Fundamentals and applications Manh-Huong Phan *, Hua-Xin Peng * Advanced Composites Centre for Innovation and Science (ACCIS), University of Bristol, Queen’s Building, University Walk, Bristol BS8 1TR, United Kingdom Received 1 April 2007; accepted 1 May 2007 Abstract Since the discovery of the magnetoimpedance (MI) effect just over a decade ago, international research interest into the giant magnetoimpedance (GMI) effect has been growing. This article aims to provide a comprehensive summary of the GMI topic, encompassing fundamental understanding of the GMI phenomena, the processing and properties of GMI materials and the design and appli- cation of GMI-based magnetic sensors. The paper starts with the definition of GMI and an assess- ment of the current theoretical understanding of the frequency dependence of GMI. Then a detailed description of processing methods for the production of amorphous and nanocrystalline GMI mate- rials in the form of wires, ribbons and thin films is given, with an examination of the advantages and disadvantages of each technique. Properties of existing GMI materials including magnetic, mechan- ical, electrical and chemical properties are described, and a correlation between domain structures and magnetic properties is established. The influences of measuring and processing parameters on the GMI effect are systematically analysed and the underlying physical origins of hysteretic and asymmetric phenomena of GMI are explained. This enables the selection of optimal conditions to design high-performance GMI-based sensors. After discussing the material selection criteria, a range of candidate materials are evaluated and nominated for the design of GMI-based sensors. Finally, a variety of potential applications of GMI-based magnetic sensors are presented with an outlook of future research development in this field. Ó 2007 Elsevier Ltd. All rights reserved. * Corresponding authors. Tel.: +44 (0) 117 92 87697; fax: +44 (0) 117 92 72771. E-mail addresses: [email protected] (M.-H. Phan), [email protected] (H.-X. Peng). 0079-6425/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.pmatsci.2007.05.003 324 M.-H. Phan, H.-X. Peng / Progress in Materials Science 53 (2008) 323–420 Contents 1. Introduction ..................................................... 326 2. Fundamental aspects of GMI ......................................... 327 2.1. What is ‘‘giant magnetoimpedance – GMI’’? . 327 2.2. Impedance of a magnetic conductor . 327 2.3. Theoretical models . 331 2.3.1. Quasistatic model ....................................... 331 2.3.2. Eddy current model ..................................... 332 2.3.3. Domain model ......................................... 332 2.3.4. Electromagnetic model ................................... 333 2.3.5. Exchange-conductivity model............................... 334 2.3.6. Other theoretical models .................................. 335 3. Processing techniques for the production of GMI materials .................... 336 3.1. Amorphous metallic wires . 336 3.1.1. Melt spinning .......................................... 336 3.1.2. In-rotating water spinning ................................. 336 3.1.3. Taylor-wire process. ................................... 337 3.1.4. Glass-coated melt spinning ................................ 338 3.1.5. Electrodeposition ....................................... 339 3.2. Amorphous metallic ribbons . 341 3.3. Magnetic thin films . 342 3.4. Nanocrystalline magnetic alloys . 342 3.5. Comparison of fabrication technologies. 344 3.6. Techniques for glass-cover removal. 345 4. Domain structure and properties of GMI materials.......................... 345 4.1. Domain structure . 345 4.1.1. Magnetic wires ......................................... 345 4.1.2. Magnetic ribbons and films ................................ 348 4.2. Magnetic properties. 349 4.2.1. Hysteresis loops ........................................ 349 4.2.2. Permeability ........................................... 353 4.2.3. Magnetisation processes .................................. 355 4.3. Mechanical properties . 356 4.4. Electrical properties. 358 4.5. Chemical properties. 359 5. Influence of measuring parameters on GMI . .............................. 360 5.1. Alternating current . 360 5.2. Magnetic field. 361 5.3. Measuring frequency . 363 5.4. Measuring temperature . 364 6. Influence of processing parameters on GMI . .............................. 365 6.1. Effect of glass coating on GMI . 365 6.1.1. Amorphous wires ....................................... 365 6.1.2. Nanocrystalline wires .................................... 367 6.2. Effect of sample geometry on GMI . 367 6.2.1. Sample length. ......................................... 367 6.2.2. Sample thickness ....................................... 368 6.2.3. Sample surface . 369 6.2.4. Sample axes . 369 6.3. Effect of annealing on GMI . 370 M.-H. Phan, H.-X. Peng / Progress in Materials Science 53 (2008) 323–420 325 6.3.1. Conventional annealing . ................................. 370 6.3.2. Field annealing......................................... 371 6.3.3. Current annealing ....................................... 372 6.3.4. Conventional stress annealing .............................. 373 6.3.5. Simultaneous stress and magnetic field annealing................. 373 6.3.6. Simultaneous stress and current annealing...................... 373 6.3.7. Laser annealing ........................................ 374 6.4. Effect of applied stress on GMI . 374 6.5. Effect of neutron irradiation on GMI . 375 6.6. Effect of hydrogen charging on GMI . 376 6.7. Effect of pH value on GMI . 376 6.8. Effect of magnetostriction on GMI. 377 6.9. Aftereffect of GMI . 377 6.10. Effect of LC-resonance circuit on GMI . 378 7. Hysteresis and asymmetry in GMI...................................... 379 7.1. Hysteresis in GMI. 379 7.2. Asymmetry in GMI. 380 7.2.1. Asymmetrical GMI due to dc bias current ..................... 381 7.2.2. Asymmetrical GMI due to ac bias field........................ 382 7.2.3. Asymmetrical GMI due to exchange bias ...................... 383 8. Selection of GMI materials for sensor applications .......................... 384 8.1. Criteria for selecting GMI materials . 384 8.2. Evaluation of GMI materials . 385 8.2.1. Rapidly quenched wires. ................................. 385 8.2.2. Electrodeposited wires. ................................. 387 8.2.3. Rapidly quenched ribbons ................................. 388 8.2.4. Magnetic thin films...................................... 390 8.2.5. Magnetic composites..................................... 392 8.2.6. Other materials......................................... 393 8.3. Nominated GMI materials for sensor applications . 393 9. GMI sensors and their applications ..................................... 395 9.1. Types of GMI sensors . 395 9.1.1. Magnetic field sensors . ................................. 395 9.1.2. Passive, wireless magnetic field sensors ........................ 396 9.1.3. Current sensors ........................................ 397 9.1.4. Stress sensors .......................................... 397 9.2. Applications of GMI sensors . 398 9.2.1. Target detection and processes control ........................ 398 9.2.2. Space research and aerospace applications...................... 399 9.2.3. Electronic compasses and automobile uses ..................... 399 9.2.4. High-density information storage ............................ 399 9.2.5. Traffic controls......................................... 400 9.2.6. Non-destructive crack detection ............................. 401 9.2.7. Biological detection...................................... 401 9.2.8. Magnetic anomaly detection and geomagnetism.................. 402 9.2.9. Stress sensing applications ................................. 402 9.3. GMI as a research tool . 403 10. Concluding remarks and future perspectives . ............................. 404 Acknowledgements................................................ 406 References . .................................................... 407 326 M.-H. Phan, H.-X. Peng / Progress in Materials Science 53 (2008) 323–420 1. Introduction Magnetic sensors play an essential role in modern technology. They are widely used in nearly all engineering and industrial sectors, such as high-density magnetic recording, nav- igation, military and security, target detection and tracking, antitheft systems, non- destructive testing, magnetic marking and labelling, geomagnetic measurements, space research, measurements of magnetic fields onboard spacecraft and biomagnetic measure- ments in the human body [1–3]. A wide range of magnetic sensors, such as induction sensors, fluxgate sensors, Hall- effect magnetic sensors, magneto-optical sensors, giant magnetoresistive (GMR) sensors, resonance magnetometers, and superconducting quantum interference device (SQUID) gradiometers, are now available [3]. A magnetic sensor directly converts the magnetic field into a voltage or resistance with, at most, a dc current supply, and the field sensi- tivity of a magnetic sensor plays a key role in determining its operating regime and potential applications. For instance, SQUID gradiometers with a high sensitivity of 10À10–10À4 Oe have been used for measuring field gradients or differences due to perma- nent dipole magnets in major applications
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