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Induced transverse magnetic anisotropy and domain structure in Co-based amorphous ribbons
~
ELSEVIER
Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
journalof magnetism ~ l ~ and magnetic materials
Induced transverse magnetic anisotropy and domain structure in Co-based amorphous ribbons R. Kolano a,,, M. Ku~mifiski b, W. Gawior a, N. W6jcik a a Institute of Non-Ferrous Metals, Sowifiskiego 5, 44-100 Gliwice, Poland b Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Abstract The influence of transverse magnetic field annealing on a domain structure, the value of the induced transverse magnetic anisotropy Ku, coercivity and magnetic remanence of Co71.sFe2.5Mn2Mo1Si9B14 amorphous ribbons of different widths (6, 11, 15 mm) has been investigated. Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J / m 3 were obtained for the transverse magnetic field H T = 160 k A / m . On the other hand, only partial reorientation of the easy axis was developed for smaller values of H T. In the initial magnetizing field range, the magnetization process proceeds by reversible rotation of the magnetization vector for H T = 160 k A / m . Domain wall movements are predominant for H T = 8 and
40 kA/m.
1. Introduction Until now, a large number of papers on induced transverse magnetic anisotropy in near-zero magnetostrictive Co-based amorphous ribbons have been reported. Most of them contain results of investigation about kinetics of the transverse field annealing process [1-3]. On the other hand, only few papers present the problem of induced transverse magnetic anisotropy in connection with domain structure observations. The experimental dependence of the average domain width on the anisotropy constant K u was established in Ref. [4]. A relationship between the magnetization process and domain structure in the stress-annealed Co70.3 Fe4.7SilsB10 glass ribbons was investigated in Ref. [5]. In this work, the transverse magnetic field annealing effect on the domain structure, induced anisotropy Ku, magnetic r e m a n e n c e Br, coercivity H c and the
* Corresponding author. Tel: +48 (32) 380412; fax: +48 (32) 316933.
initial magnetic permeability of Co71.sFezsMn2MolSi9 B14 amorphous ribbons of different widths were studied.
2. Experimental The near-zero magnetostrictive amorphous Co71.5 FezsMn2MolSi9B14 ribbons, 6, 11 and 15 mm wide and about 30 Ixm thick, were melt-spun by the planar flow casting (PFC) method. Amorphicity of ribbons was tested by X-ray diffraction. Samples for magnetic annealing had the form of 2 0 x 15 x6(11,15) mm toroidal cores and 30 mm long stripes, cut from ribbons. The magnetic annealing was made in two steps. In the first step, the samples were heated to 570 K and annealed at this temperature for 5 min. In the second step the samples were cooled to room temperature at a rate of 3 K / r a i n in a transverse magnetic field H T = 8-160 k A / m . The air surface domain structures of stripes of widths d = 6, 11, 15 mm as a function of H T were observed by means of the magneto-optical Kerr effect [6]. The dc and ac magnetic remanence B r and coercivity H c were measured along the ribbon casting
0304-8853/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-8853(94)00127-D
322
R. Kolano et al. /Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
Table 1 Physical and dc magnetic properties of the as-quenched ribbon Bso (T)
Br (T)
Hc (A/m)
Tc (K)
Tx (K)
P ( ~ cm)
0.78-0.79
0.73-0.74
0.5-0.6
670
750
115
initial m a g n e t i c p e r m e a b i l i t y / x i was m e a s u r e d at H = 0.16 A / m . For H T = 8 - 4 0 k A / m , the induced transverse-anisotropy value K u was calculated from the increase in m a g n e t i z a t i o n due to a n n e a l i n g with respect to t h a t b e f o r e a n n e a l i n g [8]. F o r higher H x = 8 0 160 k A / m , K u was evaluated from the relationship:
Ku ( h a r d ) direction ( R D ) by the c o m m u t a t i o n m e t h o d , a n d by the M a g n e t - P h y s i k Dr. Steingroever G m b H comp u t e r system R E M A C O M P [7], using t h e sinusoidal induction excitation, respectively. T h e stripe and core
//KMs 2 '
(1)
w h e r e H K d e n o t e s the s a t u r a t i o n field, d e t e r m i n e d by extrapolation of the n e a r - l i n e a r m a g n e t i z a t i o n curve to the f e r r o m a g n e t i c saturation, w h e n the m a g n e t i c field is applied parallel to the r i b b o n axis.
b)
b)
c)
l° 2.5 mm
I° 2.5 m m
Fig. 1. Domain structures C071.5Fe2.5Mn2MolSi9BI4 stripes of different widths (d) for transverse magnetic field annealing at H w = 160 k A / m (a) d = 15 mm (only 12 mm is shown), (b) d = l l mm,(c) d = 6 m m .
Fig. 2. Domain structures C071.sFe2.sMn2MolSi9B14 stripes of different widths (d) for transverse magnetic field annealing at H T = 40 kA/m. (a) d = 15 mm (only 12 mm is shown), (b) d = l l mm,(c) d = 6 m m .
R. Kolano et al. / Journal of Magnetism and Magnetic Materials 133 (1994) 321-324 3. R e s u l t s a n d d i s c u s s i o n
6000 ]
T h e initial physical a n d m a g n e t i c (dc) p r o p e r t i e s of t h e Co 7~.5Fe 2.5M n 2 M o ~Si 9 B ~4 a m o r p h o u s a s - q u e n c h e d ribbons are collected in T a b l e 1. Fig, 1 shows the d o m a i n structures in the d e m a g n e tizing state of t h e different width samples, a n n e a l e d at H T = 160 k A / m . Such a n a r r a n g e m e n t of d o m a i n s proves the near-full r e o r i e n t a t i o n of the stripe easy axis from the longitudinal to the transverse direction. Moreover, the n a r r o w e r stripes have smaller average d o m a i n widths. F o r d = 6 a n d 11 m m (Fig. lb,c), an increase in the n u m b e r of t h e edge d o m a i n s is clearly seen. T h e s e are caused by the h i g h e r d e m a g n e t i z i n g
~
H=
>,
5000
323
4000 ~ °
. . . .
". . . .o. .
"•'"
" ,O--
'~'
•
'~
.,t
o
o
~,
--
.
~
i~
A,,
.
.
~
i i ~ 160 kA/m
~
.
.
80 kA/m
"
•
O
3000 [
2000
"
1000 t 0
*
~'
~r
40 kA/m
~::~
r" :m I--SE! ~_:::::~::::~3.SkAJrn
2
4
/ 0
6 f [kHz]
8
10
12
TillYymb~ls for 5mm ~ opffn symboqs for 1 5 ~ m [
Fig. 4. Frequency dependence of amorphous C071.sFe2.sMn2 MolSigBI4 ribbons of initial permeability /zi, measured at 0.16 A / m , after field annealing at different H T.
b)
c) A RD
2.5mm I
factor. F u r t h e r m o r e , the o b s e r v e d d e f o r m a t i o n of t h e d o m a i n walls p r o b a b l y results from i n h o m o g e n e i t y of H T a n d defects in the r i b b o n surface. In c o m p a r i s o n with H T = 160 k A / m for H x = 120 a n d 80 k A / m , n o essential c h a n g e s in the d o m a i n s t r u c t u r e were observed. O n the o t h e r h a n d , Fig. 2 shows drastic c h a n g e s in the d o m a i n s t r u c t u r e after a n n e a l i n g at H T = 40 k A / m . T h e s h a p e of d o m a i n walls a n d t h e i r irregular distribution indicate t h a t such an external transverse m a g n e t i c field does n o t c o m p e n s a t e an action of the d e m a g n e t i z ing field. T h e effect arises and the d o m a i n s b e c o m e smaller with decreasing stripe widths (Fig. 2b, c). T h e very i n t e r e s t i n g d o m a i n structure shown in Fig. 3 was o b s e r v e d o n the samples a n n e a l e d at H T = 8 k A / m . W e believe t h a t this kind of structure a p p e a r s only in the n e a r - z e r o magnetostrictive a m o r p h o u s ribbons. In
6000
120
5000
100
4000
80
~ 3000
60
2000
4o ~,
1000
20
0 I
0
20
40
0 60 80 100 120 140 160 H T [kA/m]
5mm -~15mm-~Ku Fig. 3. Domain structures Co71.sFe2.5Mn2MolSi9B14 stripes of different widths (d) for the transverse magnetic field annealing at H I = 8 kA/m. (a) d = 1 5 mm (only 12 mm is shown), (b) d = 11 mm, (c) d = 6 mm.
~
I
Fig. 5. Initial permeability P-i (Hrn = 0.16 A / m , f = 5 kHz) and induced transverse magnetic anisotropy K u dependence on transverse magnetic field H T.
324
R. Kolano et al. /Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
0.5
14 12
0.4
10 E 'O
1-
0.3 E
8 \ \ Br (De) ",,~ t1~
6
_ ~'-
Hc (AC)
0.2 '~
4 0.1
2 0 0
20
40
: * - i °--, :--- 0 60 80 100 120 140 160 H T [kA/m]
Fig. 6. dc and ac ( f = 1 kHz) magnetic remanence B r and coercivity H e versus transverse magnetic field H T.
the centre of the samples (particularly for widths of 15 and 11 mm; Fig. 3a,b) the orientation of the domains is parallel to the direction of H x. However, near the edges of stripes, the orientation changes gradually towards the longitudinal direction, reflecting an increasing contribution of the primary (longitudinal) asquenched anisotropy. This effect is stronger in the narrower stripes (Fig. 3b, c). Based on Ref. [9], the value of the transverse demagnetization field at a distance of 0.1 mm from the edge of stripe was estimated to be 9.6 k A / m which is very close to H T = 8 k A / m . Because this demagnetizing field disappears very quickly with the distance from the edge, we assume that for 2 mm from the edge it disappears completely. Thus, the demagnetization field value and its behaviour can explain the results in Fig. 3. Fig. 4 shows the frequency dependence of the initial magnetic permeability /ff,i for the different H x and stripe widths. For H T = 160 k A / m , /d,i is nearly constant due to the magnetization process, which proceeds by reversible rotation of the magnetization vector in small areas of the sample, as suggested in Ref. [2] and experimentally confirmed in Ref. [10]. O n the other hand, at H x = 8 and 40 k A / m /z i drops very strongly for f = 0 - 2 kHz, indicating that domain wall movement is the main mechanism of the magnetization process in this frequency range. D o m a i n structure differences are also responsible for the higher permeability of the 15 mm wide stripes. The initial permeability and the transverse induced
anisotropy as a function of H T for the 6 and 15 mm wide stripes are shown in Fig. 5. As can be seen, the curves tend to saturation with increase of H x, but only the 15 mm wide stripes reach the saturation of P,i for the highest values (120-160 k A / m ) of H x. The practically important H x functions of the static (dc) and dynamic (ac) remanence B r and coercivity H c are shown in Fig. 6. They define a range of hysteresis loop parameters, which can be obtained by applying the transverse magnetic field during heat treatment process. From Figs. 5 and 6, it is obvious that the smallest B r and H c result from the highest value of g u•
4. Conclusions Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J / m 3 are obtained for a transverse magnetic field of 160 k A / m . Moreover, narrower stripes have smaller average domain widths. On the other hand, only partial reorientation of the easy axis is developed for lower transverse magnetic field values. For H x = 160 k A / m , the magnetization process proceeds by reversible rotation of the magnetization vector. But for H T = 8 and 40 k A / m , the magnetization process by moving of domain wall movements predominate,
References [1] [2] [3] [4] [5] [6]
[7] [8] [9] [10]
H. Kronmiiller, Phys. Stat. Solidi (b) 118 (1983) 661. T. Jagielifiski, J. Appl. Phys. 53 (1982) 7855. Y. Ochiai, K. Aso et al., J. Appl. Phys. 53 (1982) 7858. J.D. Livingston, W.G. Morris and T. Jagielifiski, IEEE Trans. Magn. 19 (1983) 1916. K. Zfiv~ta, O.V. Nielsen and K. Jurek, J. Magn. Magn. Mater. 117 (1992) 61. M. Ku~mifiski, J. Fink-Finowicki and A. Siemko, Proc. Nat. Conf. on Magnetic Measurements'92, Prague, Czech Republic, 1992. S. Siebert, Magnet-Physik Dr. Steingroever GmbH News 3 (1992) 1. J. Gonzfilez and K. Kulakowski, J. Magn. Magn. Mater. 82 (1989) 94. M.A. Rozenblat, Zurn. Techn. Fiz. 24 (1954) 637 (in Russian). T. Sawa, S. Hashimoto and K. Inomoto, IEEE Trans. Magn. 23 (1987) 3509.
ELSEVIER
Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
journalof magnetism ~ l ~ and magnetic materials
Induced transverse magnetic anisotropy and domain structure in Co-based amorphous ribbons R. Kolano a,,, M. Ku~mifiski b, W. Gawior a, N. W6jcik a a Institute of Non-Ferrous Metals, Sowifiskiego 5, 44-100 Gliwice, Poland b Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
Abstract The influence of transverse magnetic field annealing on a domain structure, the value of the induced transverse magnetic anisotropy Ku, coercivity and magnetic remanence of Co71.sFe2.5Mn2Mo1Si9B14 amorphous ribbons of different widths (6, 11, 15 mm) has been investigated. Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J / m 3 were obtained for the transverse magnetic field H T = 160 k A / m . On the other hand, only partial reorientation of the easy axis was developed for smaller values of H T. In the initial magnetizing field range, the magnetization process proceeds by reversible rotation of the magnetization vector for H T = 160 k A / m . Domain wall movements are predominant for H T = 8 and
40 kA/m.
1. Introduction Until now, a large number of papers on induced transverse magnetic anisotropy in near-zero magnetostrictive Co-based amorphous ribbons have been reported. Most of them contain results of investigation about kinetics of the transverse field annealing process [1-3]. On the other hand, only few papers present the problem of induced transverse magnetic anisotropy in connection with domain structure observations. The experimental dependence of the average domain width on the anisotropy constant K u was established in Ref. [4]. A relationship between the magnetization process and domain structure in the stress-annealed Co70.3 Fe4.7SilsB10 glass ribbons was investigated in Ref. [5]. In this work, the transverse magnetic field annealing effect on the domain structure, induced anisotropy Ku, magnetic r e m a n e n c e Br, coercivity H c and the
* Corresponding author. Tel: +48 (32) 380412; fax: +48 (32) 316933.
initial magnetic permeability of Co71.sFezsMn2MolSi9 B14 amorphous ribbons of different widths were studied.
2. Experimental The near-zero magnetostrictive amorphous Co71.5 FezsMn2MolSi9B14 ribbons, 6, 11 and 15 mm wide and about 30 Ixm thick, were melt-spun by the planar flow casting (PFC) method. Amorphicity of ribbons was tested by X-ray diffraction. Samples for magnetic annealing had the form of 2 0 x 15 x6(11,15) mm toroidal cores and 30 mm long stripes, cut from ribbons. The magnetic annealing was made in two steps. In the first step, the samples were heated to 570 K and annealed at this temperature for 5 min. In the second step the samples were cooled to room temperature at a rate of 3 K / r a i n in a transverse magnetic field H T = 8-160 k A / m . The air surface domain structures of stripes of widths d = 6, 11, 15 mm as a function of H T were observed by means of the magneto-optical Kerr effect [6]. The dc and ac magnetic remanence B r and coercivity H c were measured along the ribbon casting
0304-8853/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-8853(94)00127-D
322
R. Kolano et al. /Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
Table 1 Physical and dc magnetic properties of the as-quenched ribbon Bso (T)
Br (T)
Hc (A/m)
Tc (K)
Tx (K)
P ( ~ cm)
0.78-0.79
0.73-0.74
0.5-0.6
670
750
115
initial m a g n e t i c p e r m e a b i l i t y / x i was m e a s u r e d at H = 0.16 A / m . For H T = 8 - 4 0 k A / m , the induced transverse-anisotropy value K u was calculated from the increase in m a g n e t i z a t i o n due to a n n e a l i n g with respect to t h a t b e f o r e a n n e a l i n g [8]. F o r higher H x = 8 0 160 k A / m , K u was evaluated from the relationship:
Ku ( h a r d ) direction ( R D ) by the c o m m u t a t i o n m e t h o d , a n d by the M a g n e t - P h y s i k Dr. Steingroever G m b H comp u t e r system R E M A C O M P [7], using t h e sinusoidal induction excitation, respectively. T h e stripe and core
//KMs 2 '
(1)
w h e r e H K d e n o t e s the s a t u r a t i o n field, d e t e r m i n e d by extrapolation of the n e a r - l i n e a r m a g n e t i z a t i o n curve to the f e r r o m a g n e t i c saturation, w h e n the m a g n e t i c field is applied parallel to the r i b b o n axis.
b)
b)
c)
l° 2.5 mm
I° 2.5 m m
Fig. 1. Domain structures C071.5Fe2.5Mn2MolSi9BI4 stripes of different widths (d) for transverse magnetic field annealing at H w = 160 k A / m (a) d = 15 mm (only 12 mm is shown), (b) d = l l mm,(c) d = 6 m m .
Fig. 2. Domain structures C071.sFe2.sMn2MolSi9B14 stripes of different widths (d) for transverse magnetic field annealing at H T = 40 kA/m. (a) d = 15 mm (only 12 mm is shown), (b) d = l l mm,(c) d = 6 m m .
R. Kolano et al. / Journal of Magnetism and Magnetic Materials 133 (1994) 321-324 3. R e s u l t s a n d d i s c u s s i o n
6000 ]
T h e initial physical a n d m a g n e t i c (dc) p r o p e r t i e s of t h e Co 7~.5Fe 2.5M n 2 M o ~Si 9 B ~4 a m o r p h o u s a s - q u e n c h e d ribbons are collected in T a b l e 1. Fig, 1 shows the d o m a i n structures in the d e m a g n e tizing state of t h e different width samples, a n n e a l e d at H T = 160 k A / m . Such a n a r r a n g e m e n t of d o m a i n s proves the near-full r e o r i e n t a t i o n of the stripe easy axis from the longitudinal to the transverse direction. Moreover, the n a r r o w e r stripes have smaller average d o m a i n widths. F o r d = 6 a n d 11 m m (Fig. lb,c), an increase in the n u m b e r of t h e edge d o m a i n s is clearly seen. T h e s e are caused by the h i g h e r d e m a g n e t i z i n g
~
H=
>,
5000
323
4000 ~ °
. . . .
". . . .o. .
"•'"
" ,O--
'~'
•
'~
.,t
o
o
~,
--
.
~
i~
A,,
.
.
~
i i ~ 160 kA/m
~
.
.
80 kA/m
"
•
O
3000 [
2000
"
1000 t 0
*
~'
~r
40 kA/m
~::~
r" :m I--SE! ~_:::::~::::~3.SkAJrn
2
4
/ 0
6 f [kHz]
8
10
12
TillYymb~ls for 5mm ~ opffn symboqs for 1 5 ~ m [
Fig. 4. Frequency dependence of amorphous C071.sFe2.sMn2 MolSigBI4 ribbons of initial permeability /zi, measured at 0.16 A / m , after field annealing at different H T.
b)
c) A RD
2.5mm I
factor. F u r t h e r m o r e , the o b s e r v e d d e f o r m a t i o n of t h e d o m a i n walls p r o b a b l y results from i n h o m o g e n e i t y of H T a n d defects in the r i b b o n surface. In c o m p a r i s o n with H T = 160 k A / m for H x = 120 a n d 80 k A / m , n o essential c h a n g e s in the d o m a i n s t r u c t u r e were observed. O n the o t h e r h a n d , Fig. 2 shows drastic c h a n g e s in the d o m a i n s t r u c t u r e after a n n e a l i n g at H T = 40 k A / m . T h e s h a p e of d o m a i n walls a n d t h e i r irregular distribution indicate t h a t such an external transverse m a g n e t i c field does n o t c o m p e n s a t e an action of the d e m a g n e t i z ing field. T h e effect arises and the d o m a i n s b e c o m e smaller with decreasing stripe widths (Fig. 2b, c). T h e very i n t e r e s t i n g d o m a i n structure shown in Fig. 3 was o b s e r v e d o n the samples a n n e a l e d at H T = 8 k A / m . W e believe t h a t this kind of structure a p p e a r s only in the n e a r - z e r o magnetostrictive a m o r p h o u s ribbons. In
6000
120
5000
100
4000
80
~ 3000
60
2000
4o ~,
1000
20
0 I
0
20
40
0 60 80 100 120 140 160 H T [kA/m]
5mm -~15mm-~Ku Fig. 3. Domain structures Co71.sFe2.5Mn2MolSi9B14 stripes of different widths (d) for the transverse magnetic field annealing at H I = 8 kA/m. (a) d = 1 5 mm (only 12 mm is shown), (b) d = 11 mm, (c) d = 6 mm.
~
I
Fig. 5. Initial permeability P-i (Hrn = 0.16 A / m , f = 5 kHz) and induced transverse magnetic anisotropy K u dependence on transverse magnetic field H T.
324
R. Kolano et al. /Journal of Magnetism and Magnetic Materials 133 (1994) 321-324
0.5
14 12
0.4
10 E 'O
1-
0.3 E
8 \ \ Br (De) ",,~ t1~
6
_ ~'-
Hc (AC)
0.2 '~
4 0.1
2 0 0
20
40
: * - i °--, :--- 0 60 80 100 120 140 160 H T [kA/m]
Fig. 6. dc and ac ( f = 1 kHz) magnetic remanence B r and coercivity H e versus transverse magnetic field H T.
the centre of the samples (particularly for widths of 15 and 11 mm; Fig. 3a,b) the orientation of the domains is parallel to the direction of H x. However, near the edges of stripes, the orientation changes gradually towards the longitudinal direction, reflecting an increasing contribution of the primary (longitudinal) asquenched anisotropy. This effect is stronger in the narrower stripes (Fig. 3b, c). Based on Ref. [9], the value of the transverse demagnetization field at a distance of 0.1 mm from the edge of stripe was estimated to be 9.6 k A / m which is very close to H T = 8 k A / m . Because this demagnetizing field disappears very quickly with the distance from the edge, we assume that for 2 mm from the edge it disappears completely. Thus, the demagnetization field value and its behaviour can explain the results in Fig. 3. Fig. 4 shows the frequency dependence of the initial magnetic permeability /ff,i for the different H x and stripe widths. For H T = 160 k A / m , /d,i is nearly constant due to the magnetization process, which proceeds by reversible rotation of the magnetization vector in small areas of the sample, as suggested in Ref. [2] and experimentally confirmed in Ref. [10]. O n the other hand, at H x = 8 and 40 k A / m /z i drops very strongly for f = 0 - 2 kHz, indicating that domain wall movement is the main mechanism of the magnetization process in this frequency range. D o m a i n structure differences are also responsible for the higher permeability of the 15 mm wide stripes. The initial permeability and the transverse induced
anisotropy as a function of H T for the 6 and 15 mm wide stripes are shown in Fig. 5. As can be seen, the curves tend to saturation with increase of H x, but only the 15 mm wide stripes reach the saturation of P,i for the highest values (120-160 k A / m ) of H x. The practically important H x functions of the static (dc) and dynamic (ac) remanence B r and coercivity H c are shown in Fig. 6. They define a range of hysteresis loop parameters, which can be obtained by applying the transverse magnetic field during heat treatment process. From Figs. 5 and 6, it is obvious that the smallest B r and H c result from the highest value of g u•
4. Conclusions Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J / m 3 are obtained for a transverse magnetic field of 160 k A / m . Moreover, narrower stripes have smaller average domain widths. On the other hand, only partial reorientation of the easy axis is developed for lower transverse magnetic field values. For H x = 160 k A / m , the magnetization process proceeds by reversible rotation of the magnetization vector. But for H T = 8 and 40 k A / m , the magnetization process by moving of domain wall movements predominate,
References [1] [2] [3] [4] [5] [6]
[7] [8] [9] [10]
H. Kronmiiller, Phys. Stat. Solidi (b) 118 (1983) 661. T. Jagielifiski, J. Appl. Phys. 53 (1982) 7855. Y. Ochiai, K. Aso et al., J. Appl. Phys. 53 (1982) 7858. J.D. Livingston, W.G. Morris and T. Jagielifiski, IEEE Trans. Magn. 19 (1983) 1916. K. Zfiv~ta, O.V. Nielsen and K. Jurek, J. Magn. Magn. Mater. 117 (1992) 61. M. Ku~mifiski, J. Fink-Finowicki and A. Siemko, Proc. Nat. Conf. on Magnetic Measurements'92, Prague, Czech Republic, 1992. S. Siebert, Magnet-Physik Dr. Steingroever GmbH News 3 (1992) 1. J. Gonzfilez and K. Kulakowski, J. Magn. Magn. Mater. 82 (1989) 94. M.A. Rozenblat, Zurn. Techn. Fiz. 24 (1954) 637 (in Russian). T. Sawa, S. Hashimoto and K. Inomoto, IEEE Trans. Magn. 23 (1987) 3509.