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Nearly 20 years of magnetic amorphous wire—an overview
Journal of Magnetism and Magnetic Materials 249 (2002) 1–2
Nearly 20 years of magnetic amorphous wire—an overview Floyd B. Humphrey Electrical and Computer Engineering, Boston University, 8 Saint Mary’s Street, Boston, MA 02215, USA
Abstract Amorphous magnetic wire became available about 20 years ago. During that time, many interesting characteristics attributed to the wire have been investigated. They are unique to the wire geometry, its method of fabrication and to its amorphous nature. The early history of the wire is reviewed as well as the various changes of interest as it has grown from a novelty to an established interest. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Amorphous magnetic wire; Wire geometry; Method of fabrication; History of wire
In-water quenched, amorphous magnetic metal wire [1] has been available for nearly two decades [2]. During most of this time, samples of the wire have been readily available from UNITIK [2], so that it was possible to try ideas for applications quickly using very modest resources. A widespread global interest in the unique properties of the wire was created with many potential uses of the wire being explored especially in the field of electronic devices and sensors. Early on, the demonstration of a jitterless pulse generator element [3] utilized the most curious, although not necessarily the most useful, characteristic. Re-entrant longitudinal magnetic flux reversal was observed in wire greater than about 7 cm long. Re-entrant reversal is when a magnetic sample does not exhibit a minor longitudinal hysteresis loop. When the drive field in the loop tracer is below a certain threshold, usually called H; there is practically no flux change. Above this threshold, about half the flux changes at the same field. This threshold field is very sharp, reproducible and stable. It was found in both positive and negative magnetostrictive ascast and die-drawn, tension annealed wire of all
diameters from 125 to 10 mm diameter. Many applications and devices followed utilizing the re-entrant reversal; they are listed in a review by Va! zquez et al. [4]. The re-entrant reversal disappears when the wire is annealed making magnetostriction and stress key ingredients to the understanding of the magnetic character. Wire, since it can easily be pulled and twisted, quickly became the sample of choice for those interested in magneto-elastic characteristics of magnetic metals [5,6]. Kerr domain studies demonstrated the complexity of the problem since both positive and negative magnetostrictive wire was available. For example, on the surface ‘‘Bamboo’’ domains were seen in negative magnetostrictive wire and explained by relating them to the assumed stress; however, the same domains were seen on positive magnetostrictive die-drawn wire leaving the model in doubt [7]. The electrical studies were equally complex. The axial hysteresis loop of the magnetostrictive wire with about half the flux responding to very low fields and the other half requiring modestly high
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 0 4 9 4 - 8
2
F.B. Humphrey / Journal of Magnetism and Magnetic Materials 249 (2002) 1–2
fields suggests two magnetic phases. After a quick look at the surface domain pattern, a shell–core model was introduced. The suggestion was made that residual stress from the quenching process created a region of high radial anisotropy in a shell surrounding the soft, axially magnetized core. Since the shell accounted for about one-half the flux, it amounted to 30% of the wire diameter and it was surrounding 70% of the wire as a soft core. This shell–core model has persisted even though the exact nature of the shell and core has changed. Details that are consistent with all the many experiments have been slow in appearing. Only very recently has a model been proposed that explains most of what is seen [8]. By twisting the magnetostrictive wire, the longitudinal flux can be coupled to the circumferential flux that links the wire itself. This Matteucci effect [9] allows the wire to be driven longitudinally producing an output voltage observed between each end of the wire. The ability to drive the reversal using a current through the wire (circumferential field) set the stage for a major change of interest that has dominated the literature during the second decade. It became clear that the impedance of the wire could be controlled using small external fields. Named ‘‘Magneto-impedance’’ (MI), it created fresh interest in wire [10]. Complexity remained since explanations now were effected by the frequency of the excitation [11]. Moreover, wire no longer had a monopoly on useful structures since ‘‘Wire’’ could be made in many different ways, e.g., directly from the melt [12] or from thin magnetic metal films using photo lithographic methods [13]. Wire makers were also busy making a glass-covered wire [14] that changed the stress pattern by substituting a glass coating for the water quenching. More variables were added to the mix providing more
different materials for (hopefully) more applications. A recent workshop [15] has continued to expand the scope of wire technology. Hopes are high for applications of ‘‘Magnetic Nanowires’’ and arrays of ‘‘Nanowires’’ as well as other similar structures that appear in the workshop. It is clear that interest in understanding the wire and wire-like structures continues to be high and continues to expand with the hope that applications will justify this interest.
References [1] T. Matsumoto, I. Ohnaka, A. Inoue, M. Hagiwara, Scr. Metal. 15 (1981) 293. [2] UNITIKA Corp., Kyoto, Japan. [3] K. Mohri, F.B. Humphrey, J. Yamasaki, K. Okamura, IEEE Trans. Magn. Magn 20 (1984) 1409. ! [4] M. V!azquez, C. Gomez-Polo, D.X. Chen, A. Hernando, IEEE Trans. Magn. 30 (1994) 907. [5] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, J. Magn. Magn. Mater. 132 (1994) 10. [6] D. Atkinson, P.T. Squire, IEEE Trans. Magn. 30 (1994) 4782. [7] M. Takajo, J. Yamasaki, F.B. Humphrey, IEEE Trans. Magn. 29 (1993) 3484. [8] J. Yamasaki, M. Takajo, F.B. Humphrey, Domain structure of Amorphous wires, Proceedings of the Wire Workshop, Nagoya, Japan, May 26–27, 1999. [9] H. Takamure, J. Yamasaki, K. Mohri, I. Ogasawara, J. Magn. Soc. Jpn. 13(2) (1989). [10] K. Mohri, K. Bushida, M. Noda, Y. Yoshida, L.V. Panina, T. Uchiyama, IEEE Trans. Magn. 30 (1995) 2455. [11] D. Menard, A. Yelon, J. Appl. Phys. 88 (2000) 379. [12] P. Ciureanu, P. Rudkowski, G. Rudkowska, D. Menard, M. Britel, W.F. Currie, J.O. Stroem-Olsen, A. Yelon, J. Appl. Phys. 79 (1996) 5136. [13] M. Senda, O. Ishii, Y. Koshimoto, T. Tomoguki, IEEE Trans. Magn. 30 (1994) 4611. [14] H. Chiriac, T.A. Ovari, C.S. Marinescu, J. Appl. Phys. 83 (1998) 6584. [15] International Workshop on Magnetic Wires, San Sebastian, Spain, June 20–23, 2001.
Nearly 20 years of magnetic amorphous wire—an overview Floyd B. Humphrey Electrical and Computer Engineering, Boston University, 8 Saint Mary’s Street, Boston, MA 02215, USA
Abstract Amorphous magnetic wire became available about 20 years ago. During that time, many interesting characteristics attributed to the wire have been investigated. They are unique to the wire geometry, its method of fabrication and to its amorphous nature. The early history of the wire is reviewed as well as the various changes of interest as it has grown from a novelty to an established interest. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Amorphous magnetic wire; Wire geometry; Method of fabrication; History of wire
In-water quenched, amorphous magnetic metal wire [1] has been available for nearly two decades [2]. During most of this time, samples of the wire have been readily available from UNITIK [2], so that it was possible to try ideas for applications quickly using very modest resources. A widespread global interest in the unique properties of the wire was created with many potential uses of the wire being explored especially in the field of electronic devices and sensors. Early on, the demonstration of a jitterless pulse generator element [3] utilized the most curious, although not necessarily the most useful, characteristic. Re-entrant longitudinal magnetic flux reversal was observed in wire greater than about 7 cm long. Re-entrant reversal is when a magnetic sample does not exhibit a minor longitudinal hysteresis loop. When the drive field in the loop tracer is below a certain threshold, usually called H; there is practically no flux change. Above this threshold, about half the flux changes at the same field. This threshold field is very sharp, reproducible and stable. It was found in both positive and negative magnetostrictive ascast and die-drawn, tension annealed wire of all
diameters from 125 to 10 mm diameter. Many applications and devices followed utilizing the re-entrant reversal; they are listed in a review by Va! zquez et al. [4]. The re-entrant reversal disappears when the wire is annealed making magnetostriction and stress key ingredients to the understanding of the magnetic character. Wire, since it can easily be pulled and twisted, quickly became the sample of choice for those interested in magneto-elastic characteristics of magnetic metals [5,6]. Kerr domain studies demonstrated the complexity of the problem since both positive and negative magnetostrictive wire was available. For example, on the surface ‘‘Bamboo’’ domains were seen in negative magnetostrictive wire and explained by relating them to the assumed stress; however, the same domains were seen on positive magnetostrictive die-drawn wire leaving the model in doubt [7]. The electrical studies were equally complex. The axial hysteresis loop of the magnetostrictive wire with about half the flux responding to very low fields and the other half requiring modestly high
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 0 4 9 4 - 8
2
F.B. Humphrey / Journal of Magnetism and Magnetic Materials 249 (2002) 1–2
fields suggests two magnetic phases. After a quick look at the surface domain pattern, a shell–core model was introduced. The suggestion was made that residual stress from the quenching process created a region of high radial anisotropy in a shell surrounding the soft, axially magnetized core. Since the shell accounted for about one-half the flux, it amounted to 30% of the wire diameter and it was surrounding 70% of the wire as a soft core. This shell–core model has persisted even though the exact nature of the shell and core has changed. Details that are consistent with all the many experiments have been slow in appearing. Only very recently has a model been proposed that explains most of what is seen [8]. By twisting the magnetostrictive wire, the longitudinal flux can be coupled to the circumferential flux that links the wire itself. This Matteucci effect [9] allows the wire to be driven longitudinally producing an output voltage observed between each end of the wire. The ability to drive the reversal using a current through the wire (circumferential field) set the stage for a major change of interest that has dominated the literature during the second decade. It became clear that the impedance of the wire could be controlled using small external fields. Named ‘‘Magneto-impedance’’ (MI), it created fresh interest in wire [10]. Complexity remained since explanations now were effected by the frequency of the excitation [11]. Moreover, wire no longer had a monopoly on useful structures since ‘‘Wire’’ could be made in many different ways, e.g., directly from the melt [12] or from thin magnetic metal films using photo lithographic methods [13]. Wire makers were also busy making a glass-covered wire [14] that changed the stress pattern by substituting a glass coating for the water quenching. More variables were added to the mix providing more
different materials for (hopefully) more applications. A recent workshop [15] has continued to expand the scope of wire technology. Hopes are high for applications of ‘‘Magnetic Nanowires’’ and arrays of ‘‘Nanowires’’ as well as other similar structures that appear in the workshop. It is clear that interest in understanding the wire and wire-like structures continues to be high and continues to expand with the hope that applications will justify this interest.
References [1] T. Matsumoto, I. Ohnaka, A. Inoue, M. Hagiwara, Scr. Metal. 15 (1981) 293. [2] UNITIKA Corp., Kyoto, Japan. [3] K. Mohri, F.B. Humphrey, J. Yamasaki, K. Okamura, IEEE Trans. Magn. Magn 20 (1984) 1409. ! [4] M. V!azquez, C. Gomez-Polo, D.X. Chen, A. Hernando, IEEE Trans. Magn. 30 (1994) 907. [5] P.T. Squire, D. Atkinson, M.R.J. Gibbs, S. Atalay, J. Magn. Magn. Mater. 132 (1994) 10. [6] D. Atkinson, P.T. Squire, IEEE Trans. Magn. 30 (1994) 4782. [7] M. Takajo, J. Yamasaki, F.B. Humphrey, IEEE Trans. Magn. 29 (1993) 3484. [8] J. Yamasaki, M. Takajo, F.B. Humphrey, Domain structure of Amorphous wires, Proceedings of the Wire Workshop, Nagoya, Japan, May 26–27, 1999. [9] H. Takamure, J. Yamasaki, K. Mohri, I. Ogasawara, J. Magn. Soc. Jpn. 13(2) (1989). [10] K. Mohri, K. Bushida, M. Noda, Y. Yoshida, L.V. Panina, T. Uchiyama, IEEE Trans. Magn. 30 (1995) 2455. [11] D. Menard, A. Yelon, J. Appl. Phys. 88 (2000) 379. [12] P. Ciureanu, P. Rudkowski, G. Rudkowska, D. Menard, M. Britel, W.F. Currie, J.O. Stroem-Olsen, A. Yelon, J. Appl. Phys. 79 (1996) 5136. [13] M. Senda, O. Ishii, Y. Koshimoto, T. Tomoguki, IEEE Trans. Magn. 30 (1994) 4611. [14] H. Chiriac, T.A. Ovari, C.S. Marinescu, J. Appl. Phys. 83 (1998) 6584. [15] International Workshop on Magnetic Wires, San Sebastian, Spain, June 20–23, 2001.