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Thermal stability of softmagnetism and magnetic properties of Co-TM-Zr (TM = Nb, Ta)
1609
Journal of Magnetism and Magnetic Materials 54-57 (1986) 1609 1610 THERMAL Co-TM-Zr
STABILITY OF SOFTMAGNET1SM ( T M = Nb, T a )
Y. O M A T A , A. K U R O E
AND MAGNETIC
PROPERTIES
OF
a n d N. K A M I N A K A
Central Research Laboratoo', Matsushita Electric Industrial Co.. Ltd. 3-15 yagumo-nakamachi, Moriguchi Osaka, Japan
Thermal stability of softmagnetism of practical amorphous Co Nb-Zr and Co Ta-Zr films were investigated by kinetics of the relaxation of magnetism. The origin of the superiority of Co-Ta-Zr was discussed. Spin wave stiffness constants of these materials were determined by magnetization and FMR measurement. 1. Introduction Softmagnetic properties of amorphous alloys often vary by an annealing below the crystallization temperature due to structural changes [1]. Thermal stability of softmagnetism on C o - T M Zr(TM = Nb, Ta), which is popular as the practical softmagnetic alloys [2,3], was investigated by kinetics of the relaxation of magnetism. In addition, some magnetic properties on these alloys were studied. By means of magnetization and F M R measurements, spin wave stiffness constants were determined. 2. Experimental Amorphous C o - N b - Z r and C o - T a - Z r films were prepared by conventional rf-sputtering evaporation. The experimental details are similar to those reported in ref. [2]. The Film composition was analyzed by an I.C.P. analyzer. Curie temperature (T~) and saturation magne-tization (4"~M,) were measured with a vibrating sample magnetometer (VSM). A differential thermal analyzer was used to determine the crystallization temperature (Tx), and the amorphous structure was checked with X-rays. The initial permeability (/~i) of the films were measured with a vector-impedance meter at the field of 1 mOe. The F M R measurement was done at 9.24 G H z with magnetic field applied perpendicular to the film plane to check the standing spin wave resonance(SWR). 3. Results and discussions Composition of films were found to be Cos2Nbl3Zr5 and Co82Ta14Zr4 in atomic percent. Saturation magnetization, Curie temperature and crystallization temperature were summarized in table 1. To clarify the influence of structural relaxation and crystallization on softmagnetism, isothermal annealings were carried out at various temperature below Tx. Fig. la shows the /~, change of these two films versus the time for isothermal annealing at 480°C. Though these films include a similar concentration of (TM + Zr), Co T a - Z r film shows a better thermal stability than Co N b - Z r film. In both cases deterioration of t~i is abrupt and therefore the transition annealing-time " t r " was defined, where /Li becomes below 500. Then the 0304-8853/86/$03.50
time-temperature-transformation diagram was obtained by similar isothermal annealings at various temperatures (480, 500, 510, 520°C) as shown in fig. lb. " t r " at each temperature was shown with a solid line on each film. At the same time, a linear relationship was found between I / T and ln(tr) with almost the same slope in these two materials in fig. lc. This indicates that the/*i change seems to be a first-order rate reaction process, which is identical to the case of stress relief in metallic glass [4]. And then, the activation energy in this process is found to be almost the same for the two materials. The temperature obtained by extrapolating the solid lines to the vertical axis in the T T T diagram (fig. lb) is fairly close to Tx of each material determined by differential thermal analizer. So the deterioration of /*i seems to be mainly caused by beginning of crystallization and this is substantially supported by X-ray diffraction data. Furthermore, any structural relaxation possibly happened before the very beginning of crystallization does not cause significant deterioration on softmagnetism of such C o - T M - Z r alloy. In order to study the influence of structural relaxation on magnetic properties, F M R was observed. The change of standing spin wave resonance(SWR) was checked before and after short-time heating within a a few minutes. Results are shown in fig. 2. F M R spectra of as sputtered Co T a - Z r consists of more than one mode. On the other hand, the spectra of C o - N b - Z r is uniform. After heating at 480°C, both of F M R spectrum show clear SWR mode as can be seen in fig. 2. It is considered that heating below TX modified the atomic chemical short range order [5]. Maybe the disappearance of the complex mode of C o - T a - Z r spectra was caused by this ordering in structural relaxation [6]. The spectra of Co N b - Z r after heating is more distinct than that of Table 1 The properties of samples T~ (°C) Cos2Nb13Zr 5 480 Co~2Ta14Zr4 468
Tx (°C)
4"~Ms DFM R * (G) (meV A 2)
(meV A 2)
560 605
7550 6660
59.5 79.3
• FMR data were measured at 20°C.
'~ E l s e v i e r S c i e n c e P u b l i s h e r s B.V.
71.0 106
DMag
1610
E Omata et al. / Softrnagnetism of Co- T M - Zr
Co-To-Zr
10~ .
.
.
.
.
.
.
.
.
.
.
.
~10 2
.
Temp--480"C i\
! \
4L/" /"
1Q
(c) x10-3
Annecdincl
Time
1.25
(rain.)
1.30 1.35 1/1- (K")
(b) C.~o-Ta-Zr Co-Nb-Zr -o--'~'~-- ~ ~ - ~ .
.
.
~ L o w ~i •
: °_0~:...~_..,__.~__- -_--._
.
H,gh Hi r e g i o n - - ~ ~ 1~' - - * ~ ' ~ " - * ~ lJ~> 500
F-
p~ -*
|
16
region <500
I
10 2 Time (min)
1'0 3
10 4
Fig. 1. (a) Thermal stability of initial permeability in isothermal annealing at 480°C. Transition annealing-tmae; "'tr'" was defined as the time where /~i becomes below 500; (b) time-temperature-transformation diagram. Solid lines show "tr" at each temperature (triangle marks). Down-side of each line means the high ~i region (/~i > 500). O, ~zi > 500; o,/~i < 500 (Co-Nb-Zr). [], /~, > 500; l , ~i < 500 (Co-Ta-Zr); (c) 1 / T versus In (tr) plot of Co-TM-Zr. C o - T a - Z r a n d this suggests that the relaxation speed of C o - T a - Z r is lower t h a n that of C o - N b - Z r . In conclusion, the facts described above suggest that the relaxation process a n d speed before crystallization seems to determine the difference of stability of softm a g n e t i s m between C o - N b - Z r a n d C o - T a - Z r while activation energy derived from fig. l c is similar. 4. Spin wave stiffness constant S W R modes follow well the quadratic dispersion law o n b o t h materials. F r o m the classical relation, the spin
(a) Co- Nb-Zr after heating
~U
(b)
~
Co-Ta-Zr
J
d__E
dt
!
[/[
F--
TO000
H (Oe)
1I000
10000
I10O0
H (Oe)
Fig. 2. Standing spin wave spectrum of Co-'Nb-Zr (a) and C o - T a - Z r (b) at 20°C. Up-side and down-side are after shorttime heating at 480°C and as sputtered, respectively.
wave stiffness constant D was investigated by the following equation. H 0 - 1t,, = ( D / g t x B ) ( ~ r / t ) 2 n 2,
where H 0 a n d H , are resonance fields for the uniform a n d n t h mode, respectively, t is the film thickness and n is the n u m b e r of the mode. (n = 0, 1, 2, 3 .... mode n u m b e r s were estimated to get the best fit.) Calculated D values were described in table 1. O n the other h a n d D values were determined from the coefficient of T 3/2 in the relation of low temperature magnetization. ; M = M0(1 - B T 3/2 + ... ), where T < T J 3 . B is related with D by B = 2 . 6 1 2 [ g # B / M o ] ( k B / 4 ~ r D ) 3/2 and for the g factor the value observed from the F M R m e a s u r e m e n t was used. The results were also described in table 1. Some disagreements in table 1 may be due to the existence of oxidation layer a n d the temperature dependence of the stiffness constant [7]. The authors t h a n k Dr. F. Kobayashi for his encouragement a n d support in this work. [1] H.S. Chen and E. Coleman, Appl. Phys. Lett. 28 (1976) 245. [2] H. Sakakima, IEEE Trans. Magn. MAG-19 (1983) 131. [3] Y. Hoshi, H. Kazama, M. Nose and S. Yamanaka, IEEE Trans. Magn. MAG-19 (1983) 1958. [4] N.A. Pratten and M.G. Scott, Rapidly Quenched Metals 111 (The Metals Society, London, 1978). [5] T. Egami, Mater. Res. Bull. 13 (1978) 557. [6] M. Tarhouni, R. Krishnan, M. Tessier and J. Sztern, J. Magn. Magn. Mat. 34 (1983) 1581. [7] B. Hoekstra, R.P. Van Stapele and J.M. Robert, J. Appl. Phys. 48 (1977) 382.
Journal of Magnetism and Magnetic Materials 54-57 (1986) 1609 1610 THERMAL Co-TM-Zr
STABILITY OF SOFTMAGNET1SM ( T M = Nb, T a )
Y. O M A T A , A. K U R O E
AND MAGNETIC
PROPERTIES
OF
a n d N. K A M I N A K A
Central Research Laboratoo', Matsushita Electric Industrial Co.. Ltd. 3-15 yagumo-nakamachi, Moriguchi Osaka, Japan
Thermal stability of softmagnetism of practical amorphous Co Nb-Zr and Co Ta-Zr films were investigated by kinetics of the relaxation of magnetism. The origin of the superiority of Co-Ta-Zr was discussed. Spin wave stiffness constants of these materials were determined by magnetization and FMR measurement. 1. Introduction Softmagnetic properties of amorphous alloys often vary by an annealing below the crystallization temperature due to structural changes [1]. Thermal stability of softmagnetism on C o - T M Zr(TM = Nb, Ta), which is popular as the practical softmagnetic alloys [2,3], was investigated by kinetics of the relaxation of magnetism. In addition, some magnetic properties on these alloys were studied. By means of magnetization and F M R measurements, spin wave stiffness constants were determined. 2. Experimental Amorphous C o - N b - Z r and C o - T a - Z r films were prepared by conventional rf-sputtering evaporation. The experimental details are similar to those reported in ref. [2]. The Film composition was analyzed by an I.C.P. analyzer. Curie temperature (T~) and saturation magne-tization (4"~M,) were measured with a vibrating sample magnetometer (VSM). A differential thermal analyzer was used to determine the crystallization temperature (Tx), and the amorphous structure was checked with X-rays. The initial permeability (/~i) of the films were measured with a vector-impedance meter at the field of 1 mOe. The F M R measurement was done at 9.24 G H z with magnetic field applied perpendicular to the film plane to check the standing spin wave resonance(SWR). 3. Results and discussions Composition of films were found to be Cos2Nbl3Zr5 and Co82Ta14Zr4 in atomic percent. Saturation magnetization, Curie temperature and crystallization temperature were summarized in table 1. To clarify the influence of structural relaxation and crystallization on softmagnetism, isothermal annealings were carried out at various temperature below Tx. Fig. la shows the /~, change of these two films versus the time for isothermal annealing at 480°C. Though these films include a similar concentration of (TM + Zr), Co T a - Z r film shows a better thermal stability than Co N b - Z r film. In both cases deterioration of t~i is abrupt and therefore the transition annealing-time " t r " was defined, where /Li becomes below 500. Then the 0304-8853/86/$03.50
time-temperature-transformation diagram was obtained by similar isothermal annealings at various temperatures (480, 500, 510, 520°C) as shown in fig. lb. " t r " at each temperature was shown with a solid line on each film. At the same time, a linear relationship was found between I / T and ln(tr) with almost the same slope in these two materials in fig. lc. This indicates that the/*i change seems to be a first-order rate reaction process, which is identical to the case of stress relief in metallic glass [4]. And then, the activation energy in this process is found to be almost the same for the two materials. The temperature obtained by extrapolating the solid lines to the vertical axis in the T T T diagram (fig. lb) is fairly close to Tx of each material determined by differential thermal analizer. So the deterioration of /*i seems to be mainly caused by beginning of crystallization and this is substantially supported by X-ray diffraction data. Furthermore, any structural relaxation possibly happened before the very beginning of crystallization does not cause significant deterioration on softmagnetism of such C o - T M - Z r alloy. In order to study the influence of structural relaxation on magnetic properties, F M R was observed. The change of standing spin wave resonance(SWR) was checked before and after short-time heating within a a few minutes. Results are shown in fig. 2. F M R spectra of as sputtered Co T a - Z r consists of more than one mode. On the other hand, the spectra of C o - N b - Z r is uniform. After heating at 480°C, both of F M R spectrum show clear SWR mode as can be seen in fig. 2. It is considered that heating below TX modified the atomic chemical short range order [5]. Maybe the disappearance of the complex mode of C o - T a - Z r spectra was caused by this ordering in structural relaxation [6]. The spectra of Co N b - Z r after heating is more distinct than that of Table 1 The properties of samples T~ (°C) Cos2Nb13Zr 5 480 Co~2Ta14Zr4 468
Tx (°C)
4"~Ms DFM R * (G) (meV A 2)
(meV A 2)
560 605
7550 6660
59.5 79.3
• FMR data were measured at 20°C.
'~ E l s e v i e r S c i e n c e P u b l i s h e r s B.V.
71.0 106
DMag
1610
E Omata et al. / Softrnagnetism of Co- T M - Zr
Co-To-Zr
10~ .
.
.
.
.
.
.
.
.
.
.
.
~10 2
.
Temp--480"C i\
! \
4L/" /"
1Q
(c) x10-3
Annecdincl
Time
1.25
(rain.)
1.30 1.35 1/1- (K")
(b) C.~o-Ta-Zr Co-Nb-Zr -o--'~'~-- ~ ~ - ~ .
.
.
~ L o w ~i •
: °_0~:...~_..,__.~__- -_--._
.
H,gh Hi r e g i o n - - ~ ~ 1~' - - * ~ ' ~ " - * ~ lJ~> 500
F-
p~ -*
|
16
region <500
I
10 2 Time (min)
1'0 3
10 4
Fig. 1. (a) Thermal stability of initial permeability in isothermal annealing at 480°C. Transition annealing-tmae; "'tr'" was defined as the time where /~i becomes below 500; (b) time-temperature-transformation diagram. Solid lines show "tr" at each temperature (triangle marks). Down-side of each line means the high ~i region (/~i > 500). O, ~zi > 500; o,/~i < 500 (Co-Nb-Zr). [], /~, > 500; l , ~i < 500 (Co-Ta-Zr); (c) 1 / T versus In (tr) plot of Co-TM-Zr. C o - T a - Z r a n d this suggests that the relaxation speed of C o - T a - Z r is lower t h a n that of C o - N b - Z r . In conclusion, the facts described above suggest that the relaxation process a n d speed before crystallization seems to determine the difference of stability of softm a g n e t i s m between C o - N b - Z r a n d C o - T a - Z r while activation energy derived from fig. l c is similar. 4. Spin wave stiffness constant S W R modes follow well the quadratic dispersion law o n b o t h materials. F r o m the classical relation, the spin
(a) Co- Nb-Zr after heating
~U
(b)
~
Co-Ta-Zr
J
d__E
dt
!
[/[
F--
TO000
H (Oe)
1I000
10000
I10O0
H (Oe)
Fig. 2. Standing spin wave spectrum of Co-'Nb-Zr (a) and C o - T a - Z r (b) at 20°C. Up-side and down-side are after shorttime heating at 480°C and as sputtered, respectively.
wave stiffness constant D was investigated by the following equation. H 0 - 1t,, = ( D / g t x B ) ( ~ r / t ) 2 n 2,
where H 0 a n d H , are resonance fields for the uniform a n d n t h mode, respectively, t is the film thickness and n is the n u m b e r of the mode. (n = 0, 1, 2, 3 .... mode n u m b e r s were estimated to get the best fit.) Calculated D values were described in table 1. O n the other h a n d D values were determined from the coefficient of T 3/2 in the relation of low temperature magnetization. ; M = M0(1 - B T 3/2 + ... ), where T < T J 3 . B is related with D by B = 2 . 6 1 2 [ g # B / M o ] ( k B / 4 ~ r D ) 3/2 and for the g factor the value observed from the F M R m e a s u r e m e n t was used. The results were also described in table 1. Some disagreements in table 1 may be due to the existence of oxidation layer a n d the temperature dependence of the stiffness constant [7]. The authors t h a n k Dr. F. Kobayashi for his encouragement a n d support in this work. [1] H.S. Chen and E. Coleman, Appl. Phys. Lett. 28 (1976) 245. [2] H. Sakakima, IEEE Trans. Magn. MAG-19 (1983) 131. [3] Y. Hoshi, H. Kazama, M. Nose and S. Yamanaka, IEEE Trans. Magn. MAG-19 (1983) 1958. [4] N.A. Pratten and M.G. Scott, Rapidly Quenched Metals 111 (The Metals Society, London, 1978). [5] T. Egami, Mater. Res. Bull. 13 (1978) 557. [6] M. Tarhouni, R. Krishnan, M. Tessier and J. Sztern, J. Magn. Magn. Mat. 34 (1983) 1581. [7] B. Hoekstra, R.P. Van Stapele and J.M. Robert, J. Appl. Phys. 48 (1977) 382.