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Recent developments in soft magnetic materials
Journal of Magnetism and Magnetic Materials 0 North-Holland Publishing Company
RECENT DEVELOPMENTS
7 (1978)
308-311
IN SOFT MAGNETIC MATERIALS
*
C.W. CHEN Ames Laboratory-USDOE and Department of Materials Iowa State University, Ames, Iowa 50011, USA
Science and Engineering,
Two recent developments in soft magnetic materials are reviewed. New 3% Si-Fe laminations will enable transformers to operate at higher inductions with greater efficiency and less noise. Meanwhile, bubble memory technology has been firmly established to bridge the capacity-data retrieval time gap between semiconductor memories and the electromechanical machines.
N [S]. Despite the composition similarity, HI-B offers the following advantages over the old products when used in the transformer cores: (1) an increase in premeability from 1820 to 1920 at 800 A/m (10 Oe); (2) a decrease in total energy (core) loss by 7-20% at the induction level B = 1.5 T (15000 G); (3) a decrease in exciting VA by 20-55%; and (4) a decrease in noise output by 2-7 db (A scare) [2]. Thus, transformers made of HI-B laminations can operate at higher efficiencies with less noise and less heating in metal fittings due to flux leakage. The greatest attraction of HI-B is that, as a combination of (1) and (2) the new sheets enable transformers to operate at B = 1.7 T (core loss reported at 1.66 W/kg at 60 Hz for 0.35 mm laminations), or even 1.8 T instead of the conventional 1.5 T. Physically the HI-B sheets are superior to the old products for two main reasons. The first is the better development of the Goss texture by using AlN particles as a grain-growth inhibitor in addition to MnS. Consequently, the (1 lO)[OOl] texture is more perfect with only 3” average deviation of the [OOl ] axis from the rolling direction [6]. The high degree of texture increases permeability and lowers hysteresis loss. Significantly the AlN particles are only involved in promoting the Goss-texture formation because the Anal annealing of the sheets at 1200°C in a dry hydrogen and nitrogen atmosphere removes most of AlN from the lattice [8]. Hence the final sheets are not harmed by the previously dispersed AlN particles as far as the magnetic performance of HI-B is concerned. The
The past decade has witnessed important developments in Soft magnetic materials. While new ferrites and the potential use of amorphous alloys as soft magnets will be discussed by others at the Conference, this paper deals with the advancement of transformer laminations and the emergence of a new memory technology based on magnetic bubbles. Since 1940, magnetic sheets used in transformers have been exclustively the -3% Si-Fe laminations with the (1 lO)[OOl ] preferred orientation, known as the Goss texture [ 11. For nearly 30 years the preparation of the Goss-textured Si-Fe sheets and their magnetic performances in transformers have remained static with few minor changes. In 1968, the Nippon Steel Corporation announced a new kind of textured Si-Fe laminations under the trade name ORIENTCORE HI-B [2]. The reception of HI-B was initially slow with skepticism. As a result of Nippon’s promotion and some users’ evaluations [3,4], however, HI-B has now gained 80% of the Japanese market of textured S.-Fe sheets as well as world-wide acceptance. The HI-B licensees include ARMCO, USA; ATH, West Germany; BSC, UK, Chotillon, France; Cockerill, Belgium and People’s Republic of China. Besides 0.002% acid-soluble Al, the HI-B sheets contain similar solutes and impurities to the old products, which are typically 3% Si,.O.O05% acid-insoluble Al, 0.003%, C, 0.002% S, 0.08% Mn, and 0.0006% * This work was supported by the US Energy Research and Development Administration, Division of Physical Research.
308
C. W. Chen /Recent development of soft magnetic materials
309
Table 1
Comparison between the improved and old Goss-textured 3% Si-Fe laminations of 0.30 mm thickness Old laminations Processing: Final reduction by cold rolling
Heat treatments after final reduction
Grain-growth inhibitor Surface coating: Structure and composition
Induced tensile stress in the Si-Fe sheet Grain structure: Grain diameter Average deviation of the [ 001) axis from the rolling direction Magnetic properties: Permeability at 10 Oe Induction at 800 A/m (10 Oe) Linear magnetostriction with surface coating intact [ 3 ] Total energy loss at 60 HZ, (i)B= 1.5T (ii)B= 1.7T
80% in two steps, each -4O%, separated by an anneal at 800-1000°C in a reducing atmosphere at 800°C for a few min. in wet hydrogen, then at 1200°C in dry hydrogen MnS
85-93% in one step
at 850°C for 2 min. in wet hydrogen and nitrogen, then at 1200°C for 20 h in dry hydrogen and nitrogen AlN plus MnS
one layer of glass (mainly 35% SiO2 and 17% MgO)
two layers - an inorganic deposited on a glass (mainly 24% SiO2,21% Al203 and 16% MgO) film
0.1-0.2
0.3-0.5 kg/mm2
kg/mm’
2-4 mm 7”
7-9 mm 3”
1820 1.82 T
1920 1.92 T
-0.66 x 10-e
-0.30 x 10-e
1.04 W/kg -
0.81 W/kg 1.45 W/kg
second reason is based on a new surface coating, which consists of a glass film and an inorganic insulator. Besides electrical insulation, the coating also serves other functions: (a) inducing a larger (0.3-0.5 kg/mm2 vs. 0.1-0.2 kg/mm’ in the old sheets [6]) tensile stress, thereby keeping the magnetostriction at a lower value (see data in table 1); (b) reducing the eddy-current loss more than necessary to compensate that caused by the larger grain size; and (c) acting as an “absorber” for the removal of Al203 from the %-Fe matrix. A detailed comparison between HI-B and the old sheets is given in table 1. Magnetic bubbles represent the latest dynamic development in the long history of soft magnetic
materials [ 11. It was only a decade ago that Bobeck [9] conceived the great potential of bubble domains as vehicles for data storage and processing. Today bubble memory technology has been firmly established as is reflected by the recent installation of a bubble machine in one of Bell Telephone switching offices in Detroit [lo]. The machine, called the 13A Voice Announcement System (VAS), contains four serial shift register garnet chips, each with a storage capacity of 68 121 bits. It has 32 pins for external connections and measures 3.05 X 5.59 X 1.52 cm high. The 272 484bit machine is used to record and announce “callassist” messages. The rapid emergence of bubble technology is made
310
C. W. Chen /Recent
development
possible through spectacular advances in bubble physics, materials and device design. Theoretical analyses [ 1l-l 31 soon revealed that bubble materials must satisfy many stringent conditions in device operation [ 11. First, the material must be prepared in thin films with an uniaxial anisotropy induced normal to the film surface. To support bubbles and to minimize the bubble size, limits are imposed on the quality factor and the film thickness. To attain high bubble mobility and to avoid dynamic conversion, optimum values are suggested for the gyromagnetic ratio, the Gilbert damping parameter and the exchange stiffness. Finally, to maintain low coercivity and to ensure reliable performance of the device, the film must display composition homogeneity, thickness uniformity, low density of “magnetic defects”, low coefficient of magnetostriction, insensitivity of saturation magnetization to temperature in the 0-100°C range, and small collapse field. Under these conditions only two types of bubble materials survived the screening: the uniaxial garnets and the amorphous Cd-M alloys, where M is Co or Fe. The Cd-Co films doped with MO show a potential advantage of supporting small (
of soft magnetic materials Table 2
Bubble size, wn Circuit period, pm Storage density, bits/cm2 Data rate. bits/s
Present
Future
1977
1980
1984
l-2 I 6 X lo6 0.8 x lo6
0.3 2 5x107 5 x 106
0.1 0.7 4x10s 1 x 107
memories with more attractive features are being prepared in various laboratories. The bubble size can be reduced to 1 pm and the bit density can be raised to 250 000 bits per chip as compared with 3 pm and 68 000 bits per chip in the 13A. Garnet chips with some of these features are being marketed by Texas Instruments, Rockwell International and other companies. With further progress in materials, lithography and device design, especially in the propagation structure and chip organization, bubble memory technology is expected to advance very rapidly. A forecast recently made by Bobeck [lo] is summarized in table n
L.
The 13A VAS is described as nonvolatile (meaning no loss of information in the case of power failure), insensitive to shock, vibration and radiation and requiring low power to operate. It can access stored information in less than 2 ms, slow by random access semiconductor memory standard but ten times faster than the highest-performance disk memories. Partly for the intermediate access time, the bubble memories promise to bridge the capacity-data retrieval time gap between semiconductor memories and ferrite cores on one extreme of the spectrum and magnetic tapes, drums and disks on the other. As the bubble technology matures with reduced costs and increases in storage capacity beyond lo8 bits/cm2, the bubble technology will challenge the disk files, especially those using fixed heads [ 161 and eventually change the present memory hierarchy because the same bubble chip can perform memory, data manipulation and data processing [17]. References [l]
C.W. Chen, Magnetism and Metallurgy of Soft Magnetic Materials (North-Holland, Amsterdam, 1977). [2] S. Taguchi, T. Yamamoto and A. Sakakura, IEEE Trans. Magn., MAC&10 (1974) 123.
C. W. Chen /Recent development of soft magnetic materials [3] SM. Pegler, AIP Conf. Proc. no. 24 (1975) 718. [4] M.F. Littman, AIP Conf. Proc. no. 24 (1975) 721. [5] S. Taguchi and A. Sakakura, J. Appl. Phys. 40 (1969) 1539. [6] T. Yamamoto, S. Taguchi, A. Sakakura and T. Nozawa, IEEE Trans. Magn., MAC-8 (1972) 677. [7] F. Matsumoto, K. Kuroki and Sakakura, AIP Conf. Proc. no. 24 (1975) 716. [ 81 K. Takashima, T. Sato and F. Matsumoto, AIP Conf. Proc. no. 29 (1976) 566. [9] A.H. Bobeck, Bell Syst. Tech. J. 46 (1967) 1901.
311
[ 101 A.H. Bobeck, The Development of Bubble Memory Devices, paper presented at Electra 77 (April 1977). [ll] A.A. Thiele, Bell Syst. Tech. J. 50 (1971) 725. [12] H. Callen and R.M. Joseph, J. Appl. Phys. 42 (1971) 1977. [ 13) J.C. Slonczewski, J.C. Malozemoff and 0. Voegeli, AIP Conf. Proc. no. 10 (1972) 458. [ 141 M.H. Kryder, K.Y. Ahn and J.V. Powers, IEEE Trans. Magn., MAG-11 (1975) 1145. [ 151 J.W. Nielsen, IEEE Trans. Magn. MAG-12 (1976) 327. [16] C.D. Mee, IEEE Trans. Magn., MAC-12 (1976) 1. [ 171 H. Chang, Proc. National Computer Conf. (1974) 847.
RECENT DEVELOPMENTS
7 (1978)
308-311
IN SOFT MAGNETIC MATERIALS
*
C.W. CHEN Ames Laboratory-USDOE and Department of Materials Iowa State University, Ames, Iowa 50011, USA
Science and Engineering,
Two recent developments in soft magnetic materials are reviewed. New 3% Si-Fe laminations will enable transformers to operate at higher inductions with greater efficiency and less noise. Meanwhile, bubble memory technology has been firmly established to bridge the capacity-data retrieval time gap between semiconductor memories and the electromechanical machines.
N [S]. Despite the composition similarity, HI-B offers the following advantages over the old products when used in the transformer cores: (1) an increase in premeability from 1820 to 1920 at 800 A/m (10 Oe); (2) a decrease in total energy (core) loss by 7-20% at the induction level B = 1.5 T (15000 G); (3) a decrease in exciting VA by 20-55%; and (4) a decrease in noise output by 2-7 db (A scare) [2]. Thus, transformers made of HI-B laminations can operate at higher efficiencies with less noise and less heating in metal fittings due to flux leakage. The greatest attraction of HI-B is that, as a combination of (1) and (2) the new sheets enable transformers to operate at B = 1.7 T (core loss reported at 1.66 W/kg at 60 Hz for 0.35 mm laminations), or even 1.8 T instead of the conventional 1.5 T. Physically the HI-B sheets are superior to the old products for two main reasons. The first is the better development of the Goss texture by using AlN particles as a grain-growth inhibitor in addition to MnS. Consequently, the (1 lO)[OOl] texture is more perfect with only 3” average deviation of the [OOl ] axis from the rolling direction [6]. The high degree of texture increases permeability and lowers hysteresis loss. Significantly the AlN particles are only involved in promoting the Goss-texture formation because the Anal annealing of the sheets at 1200°C in a dry hydrogen and nitrogen atmosphere removes most of AlN from the lattice [8]. Hence the final sheets are not harmed by the previously dispersed AlN particles as far as the magnetic performance of HI-B is concerned. The
The past decade has witnessed important developments in Soft magnetic materials. While new ferrites and the potential use of amorphous alloys as soft magnets will be discussed by others at the Conference, this paper deals with the advancement of transformer laminations and the emergence of a new memory technology based on magnetic bubbles. Since 1940, magnetic sheets used in transformers have been exclustively the -3% Si-Fe laminations with the (1 lO)[OOl ] preferred orientation, known as the Goss texture [ 11. For nearly 30 years the preparation of the Goss-textured Si-Fe sheets and their magnetic performances in transformers have remained static with few minor changes. In 1968, the Nippon Steel Corporation announced a new kind of textured Si-Fe laminations under the trade name ORIENTCORE HI-B [2]. The reception of HI-B was initially slow with skepticism. As a result of Nippon’s promotion and some users’ evaluations [3,4], however, HI-B has now gained 80% of the Japanese market of textured S.-Fe sheets as well as world-wide acceptance. The HI-B licensees include ARMCO, USA; ATH, West Germany; BSC, UK, Chotillon, France; Cockerill, Belgium and People’s Republic of China. Besides 0.002% acid-soluble Al, the HI-B sheets contain similar solutes and impurities to the old products, which are typically 3% Si,.O.O05% acid-insoluble Al, 0.003%, C, 0.002% S, 0.08% Mn, and 0.0006% * This work was supported by the US Energy Research and Development Administration, Division of Physical Research.
308
C. W. Chen /Recent development of soft magnetic materials
309
Table 1
Comparison between the improved and old Goss-textured 3% Si-Fe laminations of 0.30 mm thickness Old laminations Processing: Final reduction by cold rolling
Heat treatments after final reduction
Grain-growth inhibitor Surface coating: Structure and composition
Induced tensile stress in the Si-Fe sheet Grain structure: Grain diameter Average deviation of the [ 001) axis from the rolling direction Magnetic properties: Permeability at 10 Oe Induction at 800 A/m (10 Oe) Linear magnetostriction with surface coating intact [ 3 ] Total energy loss at 60 HZ, (i)B= 1.5T (ii)B= 1.7T
80% in two steps, each -4O%, separated by an anneal at 800-1000°C in a reducing atmosphere at 800°C for a few min. in wet hydrogen, then at 1200°C in dry hydrogen MnS
85-93% in one step
at 850°C for 2 min. in wet hydrogen and nitrogen, then at 1200°C for 20 h in dry hydrogen and nitrogen AlN plus MnS
one layer of glass (mainly 35% SiO2 and 17% MgO)
two layers - an inorganic deposited on a glass (mainly 24% SiO2,21% Al203 and 16% MgO) film
0.1-0.2
0.3-0.5 kg/mm2
kg/mm’
2-4 mm 7”
7-9 mm 3”
1820 1.82 T
1920 1.92 T
-0.66 x 10-e
-0.30 x 10-e
1.04 W/kg -
0.81 W/kg 1.45 W/kg
second reason is based on a new surface coating, which consists of a glass film and an inorganic insulator. Besides electrical insulation, the coating also serves other functions: (a) inducing a larger (0.3-0.5 kg/mm2 vs. 0.1-0.2 kg/mm’ in the old sheets [6]) tensile stress, thereby keeping the magnetostriction at a lower value (see data in table 1); (b) reducing the eddy-current loss more than necessary to compensate that caused by the larger grain size; and (c) acting as an “absorber” for the removal of Al203 from the %-Fe matrix. A detailed comparison between HI-B and the old sheets is given in table 1. Magnetic bubbles represent the latest dynamic development in the long history of soft magnetic
materials [ 11. It was only a decade ago that Bobeck [9] conceived the great potential of bubble domains as vehicles for data storage and processing. Today bubble memory technology has been firmly established as is reflected by the recent installation of a bubble machine in one of Bell Telephone switching offices in Detroit [lo]. The machine, called the 13A Voice Announcement System (VAS), contains four serial shift register garnet chips, each with a storage capacity of 68 121 bits. It has 32 pins for external connections and measures 3.05 X 5.59 X 1.52 cm high. The 272 484bit machine is used to record and announce “callassist” messages. The rapid emergence of bubble technology is made
310
C. W. Chen /Recent
development
possible through spectacular advances in bubble physics, materials and device design. Theoretical analyses [ 1l-l 31 soon revealed that bubble materials must satisfy many stringent conditions in device operation [ 11. First, the material must be prepared in thin films with an uniaxial anisotropy induced normal to the film surface. To support bubbles and to minimize the bubble size, limits are imposed on the quality factor and the film thickness. To attain high bubble mobility and to avoid dynamic conversion, optimum values are suggested for the gyromagnetic ratio, the Gilbert damping parameter and the exchange stiffness. Finally, to maintain low coercivity and to ensure reliable performance of the device, the film must display composition homogeneity, thickness uniformity, low density of “magnetic defects”, low coefficient of magnetostriction, insensitivity of saturation magnetization to temperature in the 0-100°C range, and small collapse field. Under these conditions only two types of bubble materials survived the screening: the uniaxial garnets and the amorphous Cd-M alloys, where M is Co or Fe. The Cd-Co films doped with MO show a potential advantage of supporting small (
of soft magnetic materials Table 2
Bubble size, wn Circuit period, pm Storage density, bits/cm2 Data rate. bits/s
Present
Future
1977
1980
1984
l-2 I 6 X lo6 0.8 x lo6
0.3 2 5x107 5 x 106
0.1 0.7 4x10s 1 x 107
memories with more attractive features are being prepared in various laboratories. The bubble size can be reduced to 1 pm and the bit density can be raised to 250 000 bits per chip as compared with 3 pm and 68 000 bits per chip in the 13A. Garnet chips with some of these features are being marketed by Texas Instruments, Rockwell International and other companies. With further progress in materials, lithography and device design, especially in the propagation structure and chip organization, bubble memory technology is expected to advance very rapidly. A forecast recently made by Bobeck [lo] is summarized in table n
L.
The 13A VAS is described as nonvolatile (meaning no loss of information in the case of power failure), insensitive to shock, vibration and radiation and requiring low power to operate. It can access stored information in less than 2 ms, slow by random access semiconductor memory standard but ten times faster than the highest-performance disk memories. Partly for the intermediate access time, the bubble memories promise to bridge the capacity-data retrieval time gap between semiconductor memories and ferrite cores on one extreme of the spectrum and magnetic tapes, drums and disks on the other. As the bubble technology matures with reduced costs and increases in storage capacity beyond lo8 bits/cm2, the bubble technology will challenge the disk files, especially those using fixed heads [ 161 and eventually change the present memory hierarchy because the same bubble chip can perform memory, data manipulation and data processing [17]. References [l]
C.W. Chen, Magnetism and Metallurgy of Soft Magnetic Materials (North-Holland, Amsterdam, 1977). [2] S. Taguchi, T. Yamamoto and A. Sakakura, IEEE Trans. Magn., MAC&10 (1974) 123.
C. W. Chen /Recent development of soft magnetic materials [3] SM. Pegler, AIP Conf. Proc. no. 24 (1975) 718. [4] M.F. Littman, AIP Conf. Proc. no. 24 (1975) 721. [5] S. Taguchi and A. Sakakura, J. Appl. Phys. 40 (1969) 1539. [6] T. Yamamoto, S. Taguchi, A. Sakakura and T. Nozawa, IEEE Trans. Magn., MAC-8 (1972) 677. [7] F. Matsumoto, K. Kuroki and Sakakura, AIP Conf. Proc. no. 24 (1975) 716. [ 81 K. Takashima, T. Sato and F. Matsumoto, AIP Conf. Proc. no. 29 (1976) 566. [9] A.H. Bobeck, Bell Syst. Tech. J. 46 (1967) 1901.
311
[ 101 A.H. Bobeck, The Development of Bubble Memory Devices, paper presented at Electra 77 (April 1977). [ll] A.A. Thiele, Bell Syst. Tech. J. 50 (1971) 725. [12] H. Callen and R.M. Joseph, J. Appl. Phys. 42 (1971) 1977. [ 13) J.C. Slonczewski, J.C. Malozemoff and 0. Voegeli, AIP Conf. Proc. no. 10 (1972) 458. [ 141 M.H. Kryder, K.Y. Ahn and J.V. Powers, IEEE Trans. Magn., MAG-11 (1975) 1145. [ 151 J.W. Nielsen, IEEE Trans. Magn. MAG-12 (1976) 327. [16] C.D. Mee, IEEE Trans. Magn., MAC-12 (1976) 1. [ 171 H. Chang, Proc. National Computer Conf. (1974) 847.