- Email: [email protected]
Surface treatment of Finemet for reduction of power loss
Journal of Magnetism and Magnetic Materials 160 (1996) 287-288
N
~H
ELSEVIER
Journalof magnetism and magnetic materials
Surface treatment of Finemet for reduction of power loss B. Weidenfeller, W. R i e h e m a n n * lnstitut fiir Werkstoflkulzde und Werkst()ff'techt2ik, Agricolastr. 6, D 38678 Clausthal-Zellerfeld, Germany Abstract
J
Dynamical hysteresis loops of untreated and surface treated Finemet were measured in the frequency range from 20 to 60000 Hz at 0.9 T. Micro hardness indentations led to an increase of static loss caused by new pinning centres for domain walls whereas the dynamic loss in the frequency range from 40 to 50000 Hz were reduced by a domain refinement. Kevwords: Surface treatment: Finemet: Loss improvement; Domain refinement; Frequency dependence
1. Introduction
The power loss of grain oriented iron silicon steel sheets can be reduced by introducing surface defects [1-3]. Usually these defects lead to an increase of hysteresis loss while the dynamic loss is substantially decreased by domain refinement. In the case of the excellent soft magnetic material Finemet [4], which is produced by heat treatment at 580°C for I h of amorphous melt spun Fe73.sCu i Nb3Si t3.sB,), the fraction of dynamic loss is very high [5] and increases with increasing frequency. This leaves a plenty of scope for further improvement of the magnetic properties by domain refinement. 2. Experimental
The amorphous material of Fe73.sCutNb3Si13.sB9 was supplied by Vacuumschmelze (Hanau) in form of tapes 14.9 mm wide and 21 0.m thick. For magnetic measurements strips 110 mm long and 3 mm wide were cut out of these tapes. Because of the embrittlement of the nanocrystallized material the domain refining techniques such as scratching and laser scribing generally must be applied to the amorphous alloy before winding up a magnetic core. As domain refining technique a set of micro hardness indentations, 12 ixm deep and 60 txm diagonal, with 5 mm distance in strip direction and 0.15 mm in perpendicular direction was produced on the amorphous sample. This anangement of surface holes was chosen like that already used in an earlier investigation where surface defects were produced on coated grain oriented iron silicon steel sheets using Nd:YAG laser radiation [6]. The strips with the
Corresponding author. Fax: +49-5323-72-3148; email: riehemann @iww.tu-clausthal.de.
micro hardness indentations were annealed in quartz tubes under argon atmosphere at 4 × 10 4 Pa at 580°C for 1 h before they were quenched in cold water. The magnetic properties were measured in the frequency range between 20 Hz and 50 kHz with a digital hysteresis recorder which is described in more detail elsewhere [7]. 3. Results and discussion
The relative change A p ~ p in the frequency dependent power loss P ( f ) of the untreated nanocrystallized sample and the power loss of the nanocrystallized specimen with micro hardness indentations shows the effect of the surface treatment (Fig. 1). Negative values signify a reduction of power loss by micro hardness indentations. The static hysteresis loss which has been estimated by extrapolation of losses Ph = P ( . / ' ~ 0) were increased by the micro hardness indentations by 8%. Analogous to laser scribing of grain oriented iron silicon steels this can be explained by additional pinning centres to domain walls. At low frequencies the curve of the fractional loss change (Fig. 1) indicates increasing power loss due to higher hysteresis loss in surface treated sheets. In the frequency range between 40 H z - 1 2 kHz the losses are reduced by the surface treatment. The fractional loss depending on frequency has a minimum at 250 Hz, where the improvement of the loss is approximately 5%. This is probably due to a domain refinement promoted by surface treatment, which is well known for surface treated grain oriented iron silicon steels (cf. Refs. [8-10]) and is explained in the same way for Finemet, namely that in the frequency range of improvement the decrease of dynamic loss by domain refinement is higher than the increase of the static loss. At very high frequencies the loss improvement vanishes because new domain walls are nucleated with increasing frequency [1 I, 12].
0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PI1 S0304-8 85 3(96)001 43-6
B. Weidenfeller, W. Riehemann / Journal of Magnetism and Magnetic Materials 160 (1996) 287 288
288 °°5 I O.OZ-~ 8.05
Fig. 2. Using Eq. (1) and Eq. (2) the number of movable domain walls n~t of the surface treated sample is higher than the number of movable domain walls n for the untreated sample. This shows domain refinement to be the responsible mechanism for the improvement of losses. With higher frequencies the effect of domain refinement decreases due to the higher excess field at higher frequencies [14] that can create movable domain walls.
~ ....... , ",
0.02 0.01
901 ~
x
." o
-O.O2,O 0 05
c ,"
0.04 -
005
4. C o n c l u s i o n s
..m"
:o
1oo
loos FREQUENCY
/c'coo"
18,8,30{},
(az)
Fig. 1. Relative change of power loss due to micro hardness indentations at a polarization of J0 = 0.9 T.
Assuming magnetization reversal of thin sheets by planar 180 ° domain walls the magnetization theory of Williams et al. [13] leads to
a(f)
Pdyn(f) -
- 1.63--,
-
ec,(f)
(1)
d
with the average domain width a and the sample thickness d. Pdy.(f) is the frequency dependent part of the power loss P ( f ) and Pct the so-called classical loss (cf. [1]). If b is the sample width the number of moving 180 ° domain walls is given by:
n(f) = b/a(f).
(2)
Assuming the power loss to be caused by simultaneous motion of planar 180 ° domain walls their numbers were calculated from the measured power losses. The relative increase ( n s t - n ) / n of the number of domain walls by surface treatment nst in comparison to the number of domain walls of the untreated material n can be seen in
1.o t
........
'
.
.
.
.
.
o
I
,3 5 ~
"
~
c
\q Q
oo Q
9.8
lo
....
1'6o
.....
/~oc
1C000
100000
FREQUENCv (,~z)
Fig. 2. Relative increase (nst - n)/n of the number of movable 180° domain walls by surface treatment n~t in comparison to the number of domain walls of the untreated material n calculated from the power losses versus frequency at a polarization of 0.9 T.
The experiments show that a surface treatment which produces holes in the amorphous alloy before nanocrystallization can improve the magnetic properties of Finemet. The improvement can be explained by domain refinement analogous to similar experiments with grain oriented iron silicon steels. As already known for grain oriented iron silicon steels the surface holes in Finemet also increase the hysteresis loss by introducing new pinning centres for domain walls. This restricts the frequency range where an improvement is possible. In order to optimize improvement, future work will have to device treatments introducing a minimum of new pinning centres for domain walls and a maximum number of new domains. Likewise the surface treatment method must be improved for example by using lasers for surface treatment. Acknowledgement: The authors wish to thank Dr. H.R. Hilzinger, Vakuumschmelze, Hanau, for providing them with amorphous Finemet tapes. References
[1] B. Weidenfeller and W. Riehemann, J. Magn. Magn. Mater. 133 (1994) 177. [2] T. Nozawa, T. Yamamoto, Y. Matsuo and Y. Ohya, IEEE Trans. Magn. 15 (1979) 972. [3] P. Beckley, D. Snell and C. Lockhard, J. Appl. Phys. 57 (1985) 4212. [4] Y. Yoshizawa, S. Oguma and K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [5] C. Wittwer, W. Riehemann and W. Heye, J. Magn. Magn. Mater. 133 (1994) 287. [6] B. Weidenfeller, W. Riehemann and B.L. Mordike, Las. Eng. 3 (1994) 87. [7] M. Pott-Langemeyer, W. Riehemann and W. Heye, Anal. Fisica B 86 (1990) 232. [8] T. Iuchi, S. Yamaguchi, T. Ichiyama, M. Nakamura, T. Ichimoto and K. Kuroki, J. Appl. Phys. 53 (1982) 2410. [9] G.C. Rauch and R.F. Krause, J. Appl. Phys. 57 (1985) 4209. [10] M. Nakamura, K. Hirose, T. Nozawa and M. Matsuo, IEEE Trans. Magn. 23 (1987) 3074. [11] T.R. Haller and J.J. Kramer, J. Appl. Phys. 41 (1970) 1034. [12] T.R. Haller and J.J. Kramer, J. Appl. Phys. 4i (1970) 1036. [13] H.J. Williams, W. Shockley and C. Kittel, Phys. Rev. 80 (1950) 1090. [14] M. Pott-Langemeyer, W. Riehemann and W. Heye, J. Magn. Magn. Mater. 112 (1992) 284.
N
~H
ELSEVIER
Journalof magnetism and magnetic materials
Surface treatment of Finemet for reduction of power loss B. Weidenfeller, W. R i e h e m a n n * lnstitut fiir Werkstoflkulzde und Werkst()ff'techt2ik, Agricolastr. 6, D 38678 Clausthal-Zellerfeld, Germany Abstract
J
Dynamical hysteresis loops of untreated and surface treated Finemet were measured in the frequency range from 20 to 60000 Hz at 0.9 T. Micro hardness indentations led to an increase of static loss caused by new pinning centres for domain walls whereas the dynamic loss in the frequency range from 40 to 50000 Hz were reduced by a domain refinement. Kevwords: Surface treatment: Finemet: Loss improvement; Domain refinement; Frequency dependence
1. Introduction
The power loss of grain oriented iron silicon steel sheets can be reduced by introducing surface defects [1-3]. Usually these defects lead to an increase of hysteresis loss while the dynamic loss is substantially decreased by domain refinement. In the case of the excellent soft magnetic material Finemet [4], which is produced by heat treatment at 580°C for I h of amorphous melt spun Fe73.sCu i Nb3Si t3.sB,), the fraction of dynamic loss is very high [5] and increases with increasing frequency. This leaves a plenty of scope for further improvement of the magnetic properties by domain refinement. 2. Experimental
The amorphous material of Fe73.sCutNb3Si13.sB9 was supplied by Vacuumschmelze (Hanau) in form of tapes 14.9 mm wide and 21 0.m thick. For magnetic measurements strips 110 mm long and 3 mm wide were cut out of these tapes. Because of the embrittlement of the nanocrystallized material the domain refining techniques such as scratching and laser scribing generally must be applied to the amorphous alloy before winding up a magnetic core. As domain refining technique a set of micro hardness indentations, 12 ixm deep and 60 txm diagonal, with 5 mm distance in strip direction and 0.15 mm in perpendicular direction was produced on the amorphous sample. This anangement of surface holes was chosen like that already used in an earlier investigation where surface defects were produced on coated grain oriented iron silicon steel sheets using Nd:YAG laser radiation [6]. The strips with the
Corresponding author. Fax: +49-5323-72-3148; email: riehemann @iww.tu-clausthal.de.
micro hardness indentations were annealed in quartz tubes under argon atmosphere at 4 × 10 4 Pa at 580°C for 1 h before they were quenched in cold water. The magnetic properties were measured in the frequency range between 20 Hz and 50 kHz with a digital hysteresis recorder which is described in more detail elsewhere [7]. 3. Results and discussion
The relative change A p ~ p in the frequency dependent power loss P ( f ) of the untreated nanocrystallized sample and the power loss of the nanocrystallized specimen with micro hardness indentations shows the effect of the surface treatment (Fig. 1). Negative values signify a reduction of power loss by micro hardness indentations. The static hysteresis loss which has been estimated by extrapolation of losses Ph = P ( . / ' ~ 0) were increased by the micro hardness indentations by 8%. Analogous to laser scribing of grain oriented iron silicon steels this can be explained by additional pinning centres to domain walls. At low frequencies the curve of the fractional loss change (Fig. 1) indicates increasing power loss due to higher hysteresis loss in surface treated sheets. In the frequency range between 40 H z - 1 2 kHz the losses are reduced by the surface treatment. The fractional loss depending on frequency has a minimum at 250 Hz, where the improvement of the loss is approximately 5%. This is probably due to a domain refinement promoted by surface treatment, which is well known for surface treated grain oriented iron silicon steels (cf. Refs. [8-10]) and is explained in the same way for Finemet, namely that in the frequency range of improvement the decrease of dynamic loss by domain refinement is higher than the increase of the static loss. At very high frequencies the loss improvement vanishes because new domain walls are nucleated with increasing frequency [1 I, 12].
0304-8853/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PI1 S0304-8 85 3(96)001 43-6
B. Weidenfeller, W. Riehemann / Journal of Magnetism and Magnetic Materials 160 (1996) 287 288
288 °°5 I O.OZ-~ 8.05
Fig. 2. Using Eq. (1) and Eq. (2) the number of movable domain walls n~t of the surface treated sample is higher than the number of movable domain walls n for the untreated sample. This shows domain refinement to be the responsible mechanism for the improvement of losses. With higher frequencies the effect of domain refinement decreases due to the higher excess field at higher frequencies [14] that can create movable domain walls.
~ ....... , ",
0.02 0.01
901 ~
x
." o
-O.O2,O 0 05
c ,"
0.04 -
005
4. C o n c l u s i o n s
..m"
:o
1oo
loos FREQUENCY
/c'coo"
18,8,30{},
(az)
Fig. 1. Relative change of power loss due to micro hardness indentations at a polarization of J0 = 0.9 T.
Assuming magnetization reversal of thin sheets by planar 180 ° domain walls the magnetization theory of Williams et al. [13] leads to
a(f)
Pdyn(f) -
- 1.63--,
-
ec,(f)
(1)
d
with the average domain width a and the sample thickness d. Pdy.(f) is the frequency dependent part of the power loss P ( f ) and Pct the so-called classical loss (cf. [1]). If b is the sample width the number of moving 180 ° domain walls is given by:
n(f) = b/a(f).
(2)
Assuming the power loss to be caused by simultaneous motion of planar 180 ° domain walls their numbers were calculated from the measured power losses. The relative increase ( n s t - n ) / n of the number of domain walls by surface treatment nst in comparison to the number of domain walls of the untreated material n can be seen in
1.o t
........
'
.
.
.
.
.
o
I
,3 5 ~
"
~
c
\q Q
oo Q
9.8
lo
....
1'6o
.....
/~oc
1C000
100000
FREQUENCv (,~z)
Fig. 2. Relative increase (nst - n)/n of the number of movable 180° domain walls by surface treatment n~t in comparison to the number of domain walls of the untreated material n calculated from the power losses versus frequency at a polarization of 0.9 T.
The experiments show that a surface treatment which produces holes in the amorphous alloy before nanocrystallization can improve the magnetic properties of Finemet. The improvement can be explained by domain refinement analogous to similar experiments with grain oriented iron silicon steels. As already known for grain oriented iron silicon steels the surface holes in Finemet also increase the hysteresis loss by introducing new pinning centres for domain walls. This restricts the frequency range where an improvement is possible. In order to optimize improvement, future work will have to device treatments introducing a minimum of new pinning centres for domain walls and a maximum number of new domains. Likewise the surface treatment method must be improved for example by using lasers for surface treatment. Acknowledgement: The authors wish to thank Dr. H.R. Hilzinger, Vakuumschmelze, Hanau, for providing them with amorphous Finemet tapes. References
[1] B. Weidenfeller and W. Riehemann, J. Magn. Magn. Mater. 133 (1994) 177. [2] T. Nozawa, T. Yamamoto, Y. Matsuo and Y. Ohya, IEEE Trans. Magn. 15 (1979) 972. [3] P. Beckley, D. Snell and C. Lockhard, J. Appl. Phys. 57 (1985) 4212. [4] Y. Yoshizawa, S. Oguma and K. Yamauchi, J. Appl. Phys. 64 (1988) 6044. [5] C. Wittwer, W. Riehemann and W. Heye, J. Magn. Magn. Mater. 133 (1994) 287. [6] B. Weidenfeller, W. Riehemann and B.L. Mordike, Las. Eng. 3 (1994) 87. [7] M. Pott-Langemeyer, W. Riehemann and W. Heye, Anal. Fisica B 86 (1990) 232. [8] T. Iuchi, S. Yamaguchi, T. Ichiyama, M. Nakamura, T. Ichimoto and K. Kuroki, J. Appl. Phys. 53 (1982) 2410. [9] G.C. Rauch and R.F. Krause, J. Appl. Phys. 57 (1985) 4209. [10] M. Nakamura, K. Hirose, T. Nozawa and M. Matsuo, IEEE Trans. Magn. 23 (1987) 3074. [11] T.R. Haller and J.J. Kramer, J. Appl. Phys. 41 (1970) 1034. [12] T.R. Haller and J.J. Kramer, J. Appl. Phys. 4i (1970) 1036. [13] H.J. Williams, W. Shockley and C. Kittel, Phys. Rev. 80 (1950) 1090. [14] M. Pott-Langemeyer, W. Riehemann and W. Heye, J. Magn. Magn. Mater. 112 (1992) 284.