Giant Magnetoimpedance: Concepts and Recent Progress Marcelo Knobel * knobel@ifi. unicamp. br Laboratório de Materiais e Baixas Temperaturas (LMBT) Instituto de Física Gleb Wataghin (IFGW) Universidade Estadual de Campinas (UNICAMP) Campinas - SP - Brazil 5 th Conference on Magnetic Materials Measurements and Modeling (M 4) Symposium on Magnetic Sensor Materials and Devices This work is supported by FAPESP, CNPq (brazilian agencies) May 16 -17 2002 M-4 2002
Introduction The giant magnetoimpedance effect (GMI) consists in drastic changes of the complex impedance of soft magnetic materials upon the application of an external magnetic field. The GMI effect is strongly dependent on the frequency of the applied current and the magnetic anisotropies present in the material, which spawn a number of interesting new magnetic phenomena. One can roughly separate the research on GMI in approximately three aspects: (i) theory and basic research; (ii) applications; (iii) as a tool to investigate other magnetic parameters. In this talk, an updated review of all these aspects is given. M-4 2002
Presentation Outline Introduction Giant Magnetoimpedance Discovery Basic Concepts Experimental Results and Theories Quasistatic Models (Low Frequency Regime) Eddy Current Damping+Magnetic Resonance (Moderate Frequency Regime) Dynamic Effects, FMR features (High Frequency Regime) Examples on Amorphous Ribbons, Wires and Microwires; Nanocrystalline Materials; Crystalline Materials GMI as a Tool to Investigate Magnetic Properties Applications of GMI Conclusions M-4 2002 3
Acknowledgments C. Gómez-Polo, Universidad Publica de Navarra, Pamplona, Spain. M. Vázquez, CSIC, Madrid, Spain. L. Kraus, Czech Academy of Sciences, Prag, Czech Republic. J. P. Sinnecker, Universidade Federal do Rio de Janeiro, UFRJ, Brazil. M. L. Sartorelli, Universidade Federal de Santa Catarina, Florianópolis, Brazil. Fábio C. S. Silva, J. Schoenmaker, former students at LMBT, UNICAMP. Financial support: M-4 Conference, FAPESP and CNPq Conference M-4 2002 4
Collaborations M. Vázquez, A. Hernando, J. Velázquez, P. Marín, D. X. Chen, Instituto de Magnetismo Aplicado, Madrid, Spain. R. Valenzuela, Universidad Autonoma de Mexico, Mexico. M. L. Sánchez, B. Hernando, M. Tejedor, Universidad de Oviedo, Spain. H. Chiriac, Institute of Technical Physics, Iasi, Romania. R. Grössinger, R. Sato Turtelli, H. Sassik, TU Wien, Vienna, Austria. J. Gutierrez, J. M. Barandiarán, UPV, Bilbao, Spain. H. Sirkin, B. Arcondo, J. Moya, V. Cremaschi, Lab. Sólidos Amorfos, Universidad de Buenos Aires, Argentina. F. G. Gandra, C. Rettori, IFGW, UNICAMP, Brazil. M-4 2002 5
1935 ! GMI Discovery Huge and sensitive changes of the electrical impedance of soft magnetic materials upon the application of an external magnetic field. Magnetic Sensors (Amorphous Ribbons) 1991: Makhotkin et al. Amorphous Ribbons 1993 -1994: Machado, Martins and Rezende Amorphous Wires 1994: Panina and Mohri; Beach and Berkowitz; Velázquez, Vázquez, Chen and Hernando. Nanocrystalline Materials 1995: Knobel, Sánchez, Gómez-Polo, Marín, Vázquez and Hernando. Crystalline Fe-Si 1996: Carrara and Sommer. E. P. Harrison, G. L. Turney and H. Rowe, Nature 135, 961 (1935). M-4 2002 6
GMI: Evolution of Published Papers M-4 2002 7
GMI: Amorphous Wire Co 68. 25 Fe 4. 5 Si 12. 25 B 15 (Amorphous Wire) M. Knobel, M. L. Sartorelli and J. P. Sinnecker, Phys. Rev. B 55, R 3362 (1997). M-4 2002 8
Giant Magneto-Impedance (GMI) Origin: skin effect Impedance Z depends on the magnetic penetration depth m Dependence on magnetic circular permeability M-4 2002 9
Origin of GMI Skin Effect frequency High Permeability High frequency external field M-4 2002 10
THEORETICAL MODELS Main task: (Hex, f, i, . . . ) ? ? ? Low frequency regime (1 -10 k. Hz) : Quasistatic models (Machado and Rezende 1996, Atkinson and Squire 1997, 1998) Moderate frequency regime (10 k. Hz – few MHz): Eddy currents damping + magnetic resonance models (Panina and Mohri 1994, 1995) High frequency regime (dozen MHz - GHz): Dynamic effects, FMR features (Yelon et al 1996, Kraus 1998) M-4 2002 11
Double-Peak Behavior Field dependence of impedance Z (double peak behaviour) for a ribbon of composition (Fe 0. 053 Co 0. 947)70 Si 12 B 18 submited to a preannealing of one hour at 3600 C followed by one hour stressannealing at 340ºC (applied tensile stress of 400 MPa). M-4 2002
Low Frequency Regime: Quasistatic Models Minimization of free–energy density (Machado and Rezende 1996, Atkinson and Squire 1997, 1998) uniaxial anisotropy+magnetostatic (external field)+magnetostatic (transversal field)+magnetoelastic+domain wall M-4 2002
Simulation Parameters (L. Kraus, M. Knobel, et al. ISEM 97 Braunschweig): Co 70. 4 Fe 4. 6 Si 15 B 10 amorphous ribbon: Ha=1600 A/m; i=1 m. A; f=1 MHz; a=100 m; =900; =1. 5 10 -6 m; Rdc=8 ; Js=0. 5 T GMI i(r)/i(a) M-4 2002
Calculation of the current distribution Electromagnetic Description Solution of the Maxwell Equations Partial Differential Equations Simple Solutions Simple Geometries homogeneous magnetic wire isotropic Inhomogeneous Materials Complex Geometries Anisotropy Radial stress distribuiton on amoprhous wires (r) ELECTRIC FIELD E MAGNETIC FIELD B CURRENT DENSITY J Numerical Methods Iac H H Finite Element Method Fe Based Courtesy: J. P. Sinnecker circular easy axis radial M-4 2002
Courtesy: J. P. Sinnecker Current distribution of Simple Magnetic Wires (Mumetal) Frequency Dependence Field Dependence M-4 2002 16
Electroplated wires Co. P Cu How does the current flow ? Courtesy: J. P. Sinnecker M-4 2002
Finite Element Method one difficult problem Many simple problems Magnetic layer air Cu core Courtesy: J. P. Sinnecker M-4 2002
Current distribution of Electrodeposited Wires Frequency dependence 1 k. Hz Cu Co. P 100 Hz M-4 2002 19
Field distribution of Electrodeposited Wires Field Distribution Magnetic Induction M-4 2002 20
Current distribution of Electrodeposited Wires Field Dependence J. P. Sinnecker, K. R. Pirota, M. Vázquez and M. Knobel, J. Magn. Mater. (to be published) M-4 2002
Moderate Frequency Regime >> exchange lengh (Panina et al – 1995, Usov et al - 1998) Permeability tensor derived from magnetic resonance theory (neglecting exchange effects in the skin layer) Considerations: Domain structure; domain wall movements (eddy current losses): dw from effective medium approximation; magnetization rotation: rot from magnetic resonance theory. L. V. Panina, et al. IEEE Trans. Magn. 31, 1249 (1995) M-4 2002
High Frequency Regime Ferromagnetic resonance features (Yelon et al – 1996 , Ménard et al - 2000 , Kraus - 1999) Yelon et al - 1996 Connection between FMR and GMI A. Yelon, et al. Appl. Phys. Lett. 69 (20) 3084, 1996. M-4 2002
High Frequency Regime Simultaneous solution of: Landau – Lifschitz equation of motion precession Gilbert damping Bloch-Bloembergen damping Maxwell’s equations P. Ripka and L. Kraus, in: Magnetic Sensors and Magnetometers, Pavel Ripka (editor), Artech House (2001) M-4 2002 24
High Frequency Regime Ménard et al - 1998 Isotropic cilindrical wires axially saturated Landau-Lifshitz phenomenological damping term ( ) D. Ménard et al. J. Appl. Phys. 84, 2805 (1998). M-4 2002 25
High Frequency Regime Ménard et al - 2000 Anisotropic unsaturated cilindrical wires (Heff includes the anisotropy field) Comparison between theory Well defined uniaxial anisotropy, and experimental data single domain structure. Co. Fe. Si. B amorphous wire Next challange: distribution of anisotropy directions and to consider a domain structure (axially magnetized inner core in the case of wire) D. Ménard and A. Yelon. J. Appl. Phys. 88, 379 (2000). M-4 2002
High Frequency Regime Kraus - 1999 Planar conductor with uniaxial anisotropy L. Kraus, J. Magn. Mater. 195, 764 (1999). Easy axis orientation, Bloch-Bloembergen and Gilbert dampings, driving frequency, . . . Influence of easy axis direction Influence of exchange constant M-4 2002
Experimental Setup Hdc Iac Sample Courtesy: J. P. Sinnecker M-4 2002
Experimental Setup M-4 2002 29
Experimental Setup Current control Use of resistors Limited to rather low frequencies Inductive behavior of resistors at high frequencies M-4 2002 30
Experimental Setup Usual four-probe setup for measuring magnetoimpedance in the low frequency range. sample Lock-in Amplifier I = I 0 eiwt From current or voltage RF source R 1 Sample a RA R 2 to RF lock-in Setup for measuring magnetomimpedance at moderate RF frequencies. b M-4 2002 31
Experimental Setup Typical microwave cavity for measurement of the magnetoimpedance of magnetic wires at frequencies above 10 MHz. Sample Courtesy: R. L. Sommer M-4 2002 32
Recent Progress It is remarkably difficult to make a complete review of all published experimental data on GMI, because a huge amount of works have been published in the last few years. Conventional measurements are explored to test the validity of some theoretical models, while different geometries and techniques are employed to gather new insights about some unclear points. Furthermore, a great quantity of investigations deal with different kinds of materials subjected to a broad variety of annealings, which are performed in order to induce specific magnetic anisotropies, modifying the GMI response. Few selected examples will be shown in this talk. M-4 2002 33
Results: GMI vs. S (Fex. Co 1 -x)70 Si 12 B 18 (Amorphous Ribbons) M. Knobel, M. L. Sartorelli, J. Schoenmaker, J. Gutierrez and J. M. Barandiarán, Appl. Phys. Lett. 71 (15) 2208 (1997). M-4 2002 34
Nanocrystalline Materials Combined role of resistivity, permeability and induced anisotropies. Drastic reduction of Aftereffect (see below). Bad mechanical properties. M. Knobel, M. L. Sánchez, C. Gómez-Polo, A. Hernando, P. Marín and M. Vázquez, J. Appl. Phys. 79, 1646 (1996). Finemet wires M-4 2002 35
Glass Covered Microwires Hysteresis loops Co 68. 35 Fe 4. 4 Si 12. 25 B 15 microwire (metal diameter 27 m, glass coat thikness 7 m) stress-joule heated and respective HMI curves as functions of the current frequency. K. R. Pirota, L. Kraus, H. Chiriac and M. Knobel, J. Magn. Mater. L 243 Nov. (2000). M-4 2002
Fe 73. 5 Cu 1 Nb 3 Si 13. 5 B 9 amorphous films at microwave frequencies Frequency dependence of the resistance and reactance for the S 4 A sample (20 mm, annealed), for several static field strengths, showing FMR manifestation. Impedance versus field curves for S 4 (20 mm thickness) and S 4 A (annealed) samples. A. D. C. Viegas, A. M. H. de Andrade, R. L. Sommer, J. S. Jiang and C. L. Chien. J. Magn. Mater. 226 -230, 707 (2001) M-4 2002
Asymmetrical GMI Twisted wire (helical anisotropy): Iac+Idc Asymmetric arrangement of the dc magnetization L. V. Panina, et al. , J. Appl. Phys. 85 (8) 5444 (1999). Wire without torsion (circular anisotropy): Iac+coil Contribution of the cross-section magnetization process M-4 2002
Asymmetrical GMI High frequency biased field (circular anisotropy): Independent coil Also contribution from the cross-section magnetization process (off-diagonal components of impedance tensor) D. P. Makhonovski, et al. Appl. Phys. Lett. 77 (1) 121 (2000). M-4 2002
Asymmetrical GMI f = 0. 1 MHz Ha = 1 Oe Samples annealed in weak field parallel to the ribbon axis Explanation yet under discussion! (Chen et al - 2000, Kim et al. - 2000) C. G. . Kim, K. J. Jang, H. C. Kim, S. S. Yoon, J. Appl. Phys. 85 (8) 5447 (1999). M-4 2002
Granular Materials Fe. Ag granularalloy Impedance and transverse susceptibility (TS) measurements as functions of the external DC magnetic field. The peaks in both curves are in the same position and have been associated in both cases to efective anisotropy fields. J. M. Soares, J. H. de Araújo, F. A. O. Cabral, T. Dumelow, F. L. A. Machado and A. E. P. de Araújo, Appl. Phys. Lett. 80 (14) 2532 -2534 , M-4 2002
Other Systems M-4 2002
GMI as a Research Tool Material Property Authors and year Comment Fe. Co. Si. B wire Scalar circular permeability Beach, et al 1994 Fit of impedance vs frequency curve Magnetic penetration depth and circular permeability Knobel et al 1995 Real and Imaginary components of impedance as functions of field Rotational and domain wall contribution to Valenzuela et al Equivalent circuits - 1995 approach Saturation magnetostriciton constant Knobel et al 1996 Negative magnetostrictive samples Domain structure Ménard et al 1998 Glass-covered and after glass removal Ciureanu et al 1998 f 02 – H 0 plot at resoance frequency and field (straight line) Nanocrystalline Fe. Si. BCu. Nb wire Co. Fe. Si. B wire Polycrystaline Ni. Fe. Mo wires, amorphous Saturation Ni. Co- and Co. Fe-rich Magnetization (Ms) wires M-4 2002 43
GMI as a Research Tool Material Property Authors and year Comment Angular dependence of GMI Co-based Ribbon Easy axes distribution function Pirota et al – 1999 Fe. Co. Si. B wire Landau-Lifschitz damping parameter Ménard et al – 1999 Peak value of the wire impedance at resonance Ni. Co-rich wire Anisotropy field, saturation magnetization, giromagnetic ratio Britel et al. – 2000 Ferromagnetic resonance and antiresonance (110)[001]Fe. Si 3% Magnetization dynamics (reversible and irreversible parts) Carara et al – 2000 Low frequency range experiment (100 Hz – 100 k. Hz) Fe. Nb. B ribbons Anisotropy field in function of Fe content Ryu et al – 2000 Hk decreases with Fe content Co. P microtubes electrodeposited on Cu wires Domain structure Garcia et al – 2001 Combined with magnetic force microscopy M-4 2002 44
Effect of Stress on GMI AC-20 M. Knobel, M. L. Sánchez, A. Hernando and M. Vázquez, J. Magn. Mater. 169, 89 (1997). M-4 2002
Evaluation of s through GMI measurements (Less than 3% difference with SAMR method. Estimation of internal stresses from c, 270 MPa) M. Knobel, C. Gómez-Polo and M. Vázquez, J. Magn. Mater. 160, 243 (1996). M-4 2002 46
Angular Dependence of GMI Resonance condition: (for small frequencies ((w / g)2 << Ms. HK): y = 0 and H 0 » HK) Equilibrium angle : K. R. Pirota, et al. , Phys. Rev. B 60 6685 (1999). M-4 2002
Maxwell’s Equations + Landau–Lifschitz equation of motion secular equation propagation constants impedance tensor Zzz component f = 500 k. Hz Defining: HK = HK e x n F(H 0, HK) = Z/Rdc that has a sharp peak for H 0 = HK Parameters: Js = 0. 6 T, HK = 520 A/m = 6. 5 Oe, g = 2. 1, a = 0. 027, r = 1. 22 m. Wm, A = 3 10 -12 J/m, and t = 13. 7 mm M-4 2002 K. R. Pirota, L. Kraus, M. Knobel, P. G. Pagliuso, and C. Rettori, Phys. Rev. B 60 6685, 1999. Angular Dependence of GMI 48
Measurements of Ferromagnetic Resonance and Antiresonance Kittel Conditions: M. R. Britel, D. Ménard, L. G. Melo, P. Ciureanu, A. Yelon, Appl. Phys. Lett. 77 (17), 2737 (2000) M-4 2002
Modelization through Fourier Harmonic Contribution Simple Rotational Model Calculated circular hysteresis loops, M - H , (K = 19. 9 J/m 3) for H = 0. 3 Oe (solid line) and H = - 0. 3 Oe (dot line). C. Gómez-Polo, M. Vázquez and M. Knobel, Appl. Phys. Lett. 78 246 (2001) M-4 2002 50
Modelization through Fourier Harmonic Contribution Comparison between the calculated (solid line) and experimental (symbols) axial field (H) dependence of impedance components , Z = R +i X, (f = 50 k. Hz, Iac = 5 m. A) for the Joule heated wire at j = 24. 3 A/mm 2 with a dc biased current Idc = 2. 5 m. A (R: ( ); X (+)). C. Gómez-Polo, M. Vázquez and M. Knobel, Appl. Phys. Lett. 78 246 (2001) M-4 2002 51
Modelization through Fourier Harmonic Contribution Second harmonic voltage, V 2 f, as a function of the axial field, H, for the as -cast (x: Hk = 16 A/m), and Joule heated wires at j = 19. 9 ( : Hk = 30 A/m) and 24. 3 (o: Hk = 50 A/m) A/mm 2 (f = 50 k. Hz). C. Gómez-Polo, et al. , Physica B 299, 322 (2001) Calculated axial field (H) dependence of the second harmonic contribution to the magnetic permeability, , 2 f, for Hk = (x)16, ( ) 30 and (o) 50 A/m. M-4 2002
Applications Many applications of GMI have been proposed so far. By choosing an appropriate material, and performing specific thermal treatments it is possible to tailor special impedance responses, depending on the desired application. The high sensitivity of GMI to external dc field, drive current frequency and tensile stress makes soft magnetic materials specially convenient for sensor applications. Therefore, from the application point of view, many uses of GMI materials have been idealized and developed, with very interesting perspectives. M-4 2002 53
GMI: Applications Sensor Head Length Resolution Response Power Speed Consumption Hall Sensor 10 – 100 m 0. 5 Oe/ 1 k. Oe. FS 1 MHz 10 m. W MR Sensor 10 – 100 m 0. 1 Oe/ 100 Oe. FS 1 MHz 10 m. W GMR Sensor 10 – 100 m 0. 01 Oe/ 20 Oe. FS 1 MHz 10 m. W Fluxgate Sensor 10 – 20 mm 1 Oe/ 3 Oe. FS 5 k. Hz 1 W SQUID Sensor 10 – 20 mm 50 p. Oe/ 1 Oe. FS 5 k. Hz MI Sensor 1 – 2 mm 1 Oe/ 3 Oe. FS 1 MHz 10 m. W SI Sensor 1 – 5 mm 0. 1 Gal/30 Gal. FS 10 k. Hz 5 m. W K. Mohri, T. Uchiyama, L. P. Shen, Y. Honkura and H. Aoyama, International Workshop on Magnetic Wires, June 2001, San Sebastián, Spain. To be published in JMMM. M-4 2002
GMI: Applications Thin Film Magneto Impedance Sensor using micro plating process Materials for the study of the Institute of Electrical Engineers of Japan. MAG-00 -24, p 79 -84 (2000) Authors Copyright Akio Takayama, Akiyo Yuguchi, Tamio Umehara The Institute of Electrical Engineers of Japan We have developed an integrated thin film MI sensor head constructed with a combination of a thin film Ni. Fe MI element and : thin film bias and negative feedback coils using a micro-plating technology, in order to solve the problems of the amorphous wire : MI head. Ni. Fe composition (magnetostriction coefficient) of the thin film MI element is closely related to its MI characteristics, and has a great influence on stability of the sensor performances. Therefore, the relationship between Ni. Fe composition and MI characteristics was investigated in this study. We have also fabricated a differential type sensor module using a pair of the thin film MI sensor heads, and investigated its sensor performance. http: //www. minebea-ele. com/en/newproduct/J_6000. html#ronbun 03 M-4 2002
GMI: Applications Field Detection Characteristics of Differential Magnetic Sensor Using Integrated Thin-film MI Sensor Heads Journal of the Magnetics Society of Japan. 24, p 763 -766, (2000) Authors : A. Takayama, T. Umehara, A. Yuguchi, H. Kato, K. Mohri, T. Uchiyama Copyright : The Magnetics Society of Japan A thin-film MI element made using thin-film integration technology is suitable to fabricate a very small, highly reliable MI sensor head. We developed an integrated thin-film MI sensor head constructed with a combination of a thin-film Ni. Fe MI element and thin-film bias and negative feedback coils using micro-plating technology, in order to solve the problems of an amorphous wire MI head. We also fabricated a differential sensor module using a CMOS multivibrator and a pair of the thin-film MI sensor heads. The differential sensor module using a pair of the thin-film MI heads showed a sensitivity of 25 m. V/A/m (2. 0 V/Oe) with an amplifier having an amplification factor of 10 and good linearity without hysteresis. The sensor module has a thermal drift of less than 0. 008%/FS˚C at 0 A/m and 0. 028%/FS˚C at 80 A/m, at temperatures from -25 C to 75 C, and also has good stability in field detection characteristics. http: //www. minebea-ele. com/en/newproduct/J_6000. html#ronbun 03 M-4 2002
GMI: Applications Using micro plating technology, they have developed thin film MI sensor heads that have integrated Ni. Fe thin film MI elements, thin film bias coils, and thin film negative feedback coils. The magnetic field sensitivity achieved with MI elements is extremely high, at 0. 41% A/m (33%/Oe) 33%/Oe In the manufacture of differential MI sensor modules using highly sensitive thin film MI elements, when the output voltage of the sensor uses a magnitude 10 amp, it has been possible to obtain a value of 25 m. V/A/m (2. 0 V/Oe). In addition, they have been able to confirm excellent magnetic sensor characteristics with no hysteresis. Temperature characteristics, particularly in the zero magnetic field, are extremely favorable, with near-zero drift and stable magnetic field sensitivity characteristics. It is thought that MI sensors have a wide range of potential applications, such as geomagnetic sensors for CRTs and Intelligent Transport Systems (ITS), or for use as paper currency sensors. http: //www. minebea-ele. com/en/newproduct/J_0000. html M-4 2002
GMI: Applications http: //www. minebea-ele. com/en/newproduct/J_0000. html M-4 2002
GMI: Applications The Japan Science and Technology Corporation (JST) selected the following theme as new commission-basis development task and announced the enterprises to be commissioned with their development: Automobile-loaded magnetic impedance sensors "Automobile-loaded magnetic impedance sensors" given high environment resistance by strengthening the junction between the sensor head and electronic parts and compensating for the temperature stability of the high-frequency circuit is a research result of Professor Kaneo Mohri of Dept. of Electrical Engineering, Graduate School of Engineering , Nagoya University. Its development for practical use is to be commissioned to Aichi Steel Corporation (based in Tokai City, Aichi Prefecture) with the development period of 4 years and development expenditures of 600 million yen. Since a magnetic sensor is not affected by splashes of water and mud, dust and exhaust gas in its dective properties, it is used for various measurement applications including the measurement of rotation number of an axle and loaded on automobiles. However, the conventional-type magnetic sensor requires to compensate for lack of sensitivity in the precise mechanism for mechanical positioning. The magnetic impedance effects were discovered by the above-mentioned researcher, and the application development of the sensor which uses the effects has been advanced as the smallsized and low electricity-consumption sensor having the sensitivity 100 times or more as high as that of the conventional type. However, the type junction between amorphous wire the sensor head and electric terminal have destructible by mechanical oscillation. And the high-frequency circuit have been unstable to drastic temperature fluctuations, and it has been unable to utilize its properties sufficiently under such a harsh environment as being loaded on automobiles. 1999/03/04, http: //www. mext. go. jp/english/news/1999/03/990314. htm M-4 2002 59
GMI: Applications Aichi Steel Establishes Company to Develop Magnetic Impedance Sensors Nagoya, February 14, 2001 - Aichi Steel (Yuji Shibata, President) announced today at the Trade and Industry Press Club that it had established a new company, Aichi Micro Intelligent Corporation (Akiyoshi Morita, President & CEO), to research and market magnetic impedance (MI) sensors. MI sensors, which are 10, 000 times more sensitive than conventional magnetic sensors, were developed on consignment from the Japan Science and Technology Corporation. Now that a sample of a MI sensor is ready, a pilot plant has begun producing 20, 000 units per month. Aichi Steel says that the new sensor will achieve cost performance superior to traditional magnetic sensors. Dr. Ken Takemoto, professor emeritus, University of Tohoku and Dr. Kaneo Mohri, professor, University of Nagoya are responsible for this technological innovation. Dr. Takemoto invented the amorphous magnetic wire and the latter discovered the MI effect of amorphous magnetic wire. The MI sensor is based on these technologies. This MI sensor technology can be applied to automobile sensors because of its compact size and cost reduction. Moreover, it will be used in magnetic induction type non-attendance operating systems and ITS systems. This is a world-class Japanese invention. Dr. Mohri will be the director of the new company. He is the first professor of a national university to concurrently assume the title of director of a private company. Aichi Micro Intelligent, which has 20 million yen in starting capital and plans to have 15 employees, will conduct research with Japanese, American, and European users to develop products that use the MI sensor. The new company's projected sales volume is three billion yen per year, within five years http: //www. aichi-steel. co. jp/ENGLISH/TOPICS/topics 140. htm M-4 2002 60
M-4 2002 http: //www. nuee. nagoya-u. ac. jp/labs/mohrilab/world 2000. html http: //www. aichi-steel. co. jp/SPINFO/MAGAT/MI/MI_frame. html GMI: Applications 61
GMI Applications 20 December 2001 First Applied Product of the Amorphous Wire MI Sensor－ The Milli-Gaussmeter" Minute Magnetic Field Measuring Device enters the market *Trademark registration pending "Milli-Gaussmeter" Due to the superb characteristics of the MI sensor, this new product has measuring precision of 0. 1 milligauss. Other advantages brought by the MI sensor are low energy consumption, high responsiveness, portability and the ability to be used under harsh conditions. One of the products being introduced is a 3 -dimensional measurement device. This is the first time ever that pinpoint 3 -dimensional measurement has been made possible. Potential users include researchers in the biological and environmental fields, as well researchers investigating new sensing systems. It is also great appeal to many science enthusiasts. ttp: //www. aichi-steel. co. jp/ENGLISH/TOPICS/topics 151. htm M-4 2002 62
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GMI: Applications M-4 2002 64
GMI: Applications Alliance with Macnica to Expand Market in Infocommunications to Mass-produce Micro-mini, High Sensitive MI Sensor Modules for Mobile Phones A long-awaited Magnetic Checker: Dental Magnet Tester Released (Applied for trademark ) http: //www. aichi-steel. co. jp/ENGLISH/TOPICS/topics. htm M-4 2002 65
ht tp : / / w w w. ai c hi m i. c GMI: Applications M-4 2002 66
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GMI: Applications M-4 2002 70
GMI Sensors: PIG http: //mail. fis. puc-rio. br/emagnd/pig. html Non-destructive testing of oil pipelines (Brazil) (Fernando Machado) M-4 2002 71
GMI Sensors H. Hauser, L. Kraus, P. Ripka, IEEE Instr. Meas. Magazine, June 2001, p. 28, http: //www. newscientist. com/hottopics/sciencedebates/ M-4 2002 72
GMI Sensors H. Hauser, L. Kraus, P. Ripka, IEEE Instr. Meas. Magazine, June 2001, p. 28, http: //www. newscientist. com/hottopics/sciencedebates/ M-4 2002 73
GMI Stress Sensor AC-20 Amorphous Wire M. L. Sánchez, M. Knobel and D. -X. Chen, in: Nanostructured and Non-Crystalline Materials, Eds. M. Vázquez e A. Hernando, World-Scientific (Singapure), pp. 592 -597 (1995). M-4 2002
GMI Stress Sensor M-4 2002 75
Non-linear response M-4 2002 76
Impedance Relaxation Wires Co 68. 25 Fe 4. 5 Si 12. 25 B 15 amorphous wire M. Knobel, M. L. Sartorelli and J. P. Sinnecker, Phys. Rev. B 55, R 3362 (1997). M-4 2002 77
Hysteretic GMI J. P. Sinnecker, P. Tiberto, G. V. Kurlyandskaia, E. H. C. P. Sinnecker, M. Vázquez and A. Hernando, J. Appl. Phys. 84, 5814 (1998) M-4 2002 78
Conclusions Owing to the rapid development of theories and applications, supported by systematic experimental investigations, it is possible to predict a fruitful future to the GMI effect. Theories and Basic Research: Although each day the GMI phenomenon is better uderstood, there are still many points that remain to be clarified. Systematic experimental studies, supported by theoretical models, are being presently developed, in order to understand all basic aspects of this interesting effect. GMI as a tool: Once theories become more and more acurate, it will be possible to use the GMI effect as an additional tool to study soft magnetic materials, including the distribution of quenched-in and induced anisotropies, magnetoelastic behaviour, ferromagnetic resonance and anti-resonance, domain structure. Applications: There already working prototipes and devices in the market that make use of GMI, with several advantages when compared with other available sensors. The progress on models and experimental data will lead to improved materials from the applications viewpoint, mainly highly-sensitive magnetic sensors. M-4 2002 79
Conclusions There are still many unsolved problems and questions that remain to be clarified during this challanging route to understand develop better application oriented soft magnetic materials. Basic Research tool Applications An open road yet to explore. . . http: //www. ifi. unicamp. br/~knobel M-4 2002 80
The End M-4 2002 81
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