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Magnetic and structural properties of Fe films deposited by ion-beam sputtering with a high-energy assisted process
ELSEVIER
Thin Solid Films 281-282 (1996) 484-487
Magnetic and structural properties of Fe films deposited by ion-beam sputtering with a high-energy assisted process S. Iwatsubo a.*, T. Takahashi b, M. Naoe
C
a Central
Research Institute, Toyama Industrial Technology Center, 150Futagami, Takaoka, Toyama 933, Japan h FaCility of Engineering, Toyama University, 3190 Gofuk», Toyama 930, Japan C Faculty a/Engineering. Tokyo Institute ofTeclmology, 2·/2·1, Osokayama, Meguro-ku. Tokyo 152, Japan
Abstract The microstructure and lhe magnetic properties of polycrystalline Fe films were investigated in detail by controlling the condition of the ion-beam sputtering with an Ar-assisted process, Fe films were deposited at a sputtering-beam voltage, Vs, in the range of 300-1800 V. The soft magnetic properties ofthe Fefilms significantly improved with increasing Vs, when the saturation magnetization, 47TMs' and thecoercivity, He, were 16-21.5 kG and 5 Oe, respectively. This improvement was caused bythe decrease of the crystallite size. Inorder to control the Fe crystallite size, Fe films were deposited when the Ar-assisted beam voltage, VA' was in the range of 80-2000 V, with the condition that the Ar to Fearrival ratios were I: 1 (RA = ) and 1:0.1 (RA =0.1). Fe films with excellent soft magnetic properties, such as 41t'Ms ofabout 21.5 kG and He of 2.5 Oe, were deposited on the substrate and bombarded bya VA of 200 V at R", :::: I and a VA of 400V at RA =0.1. The result implies that bombardment byArions, with the proper energy and flux, assists the improvement of the softmagnetic properties. Keywords: Iron; Sputtering; Ion bombardment; Magnetic properties and measurements
1. Introduction
Recently, it has been reported that Fe-based alloy films show excellent soft magnetic properties and high thermal stability, so they have attracted strong interesi for use as magnetic recording heads in high recording density applications. However, in the case of a thin film, their magnetic properties may be affected by a small amount of impurities contained iII the film [1]. According to reports on the preparation process of films or the purity of the Fe target, values of 47TM's and He can vary significantly. Therefore, it is necessary to control the film deposition parameters during preparation, in order to attain the soft magnetic properties. The ion-beam sputtering method isadequate for the above requirement [2,3]. Bombarding ions, with an Ar-assisted process, change the IDea! temperature on the film surface or damage the film. surface. In this study, the relationship between the magnetic and the structural properties and the size of the crystallites in the films has been investigated in detail bycontrolling theconditions ofthe ion-beam sputtering with a high-energy Ar-assisted process.
... Corresponding author. 0040-6090/96/$15.00 © 1996 Elsevier Science SA All rights reserved Pll S0040·6090( 96) 08680·4
2. Experiments
Fig. 1 shows theschematic diagram of the ion-beam sputtering apparatus used in this study. Specimen films were deposited onwater-cooled glass substrates byion-beam sput\
\ \~ as (Ar)
-
I
. .. ., Sputtering ionsource I Substrate holder ,, ',
- ,..~<, "~ \ ,
\
AI ion'..
~
I
,
v.s
\
\
~
..
~
'
I
".
,
/
,
.. - . / / \, \. .. /
~
~
/ ISubstnllc /
'
;;
I
I
:
:t ,
I
~
f
I I
;
~
:
I
'
' I !. I
, !~
,
I
I
. i .' .. : :
•
'
I
Ar ion
Electron
I
Neutralizer filament
I'
, Gasassisted ionsource Gas (Ar) Fig, I. A schematic diagram of the ion-beam sputtering apparatus with a gas-assisted ionsource.
485
S, lwarsubo et al./Thill Solid Films 28/-282 (/996) 484-487
tering from an Fe target of 99.9% purity. Both of the ion sources are Kaufman-type. The residual gas pressure in the chamber was 6 X 10- 5 Pa. Pure Argas was introduced asthe sputtering gas through the sputtering-ion source up to 3.6 X 10- 3 Pa, when the gas flow rate was 2 seem. Vs was controlled in the range 300-1800 V. The total sputteringbeam current was fixed at 50 rnA. For the At-assisted ion source, VA was varied in therange 80-2000 V. The current density of the assisted ions on the substrate surface was adjusted to0.49 and 0.049 A m- 2; these were calculated from the deposition rate (3.3 nm min - I) at Vs =1200V. The films thicknesses were 300-350 nm. The 47TMs and He values were measured by a vibrating sample magnetometer. The crystal structure was analyzed by X-ray diffractometry, and the composition of the films was measured by ESCA and RBS.
3. Results and discussion 3.1. Microstructure Fig. 2 shows 8-20 X-ray diffraction patterns of as-deposited Fe films as a function of the parameter, VS I in the range 300-1800 V. The films deposited at a Vs value of 300 V exhibited the sharpest diffraction peak, butthese films contain a large amount of carbon. Therefore, this case must be neglected when considering the relationship between the sputtering particles energy andthe microstructure. Except for the same case, broad X-fay diffraction peaks from the (110) planes and (200) planes of (X-Fe were observed. The peak intensity of the (200) plane showed a tendency to decrease as Vs increased. Thepeak intensity of the ( 110) plane had a minimum value at a Vs value of 1200 V. With an increase of Vs, there was a shift from a (200) orientation to a (110)
orientation. The ( 110) peaks above Vs values of900 V were not symmetrical, which suggests that the microstructure of the films was not homogeneous. Fig. 3 shows 8-20X-ray diffraction diagrams ofas-deposited Fe films as a function of the At-assisted beam voltage, VA' when the arrival ratio of Fe to Ar was 1: I. In Fig. 3, a value of 0 V for VA means that the film is deposited without an Ar-assisted process. For the. films deposited with the Arassisted process, the X-ray diffraction peaks from the (110), (211) and (220) planes of ·!X··Fe were observed. The peak intensity of the (200) plane from the films from the Arassisted process was very weak, On the other hand, the films deposited at VA values of 200 V have a maximum value at the (110) peak intensity. Moreover, the (220) peak, which is the half-lattice distance of the (110) plane, was only observed at VA valuer! of 200 V. Peak angles of the (1 to) plane in the films were constant at about 44.4 o. The (110) peaks of the films f..om the Ar-assisted process were symmetrical. These results show that the microstructure of the films was more homogeneous than without an Ar-assisted process, and the orientation of the crystallization in the films was controlled. In the films deposited with theAr-assisted process, and the condition that the ratio of the arrival rate of Fe to Ar was i:O.l, similar X-ray diffraction diagrams were observed. When VA was 400 V, the (110) peak intensity was at its maximum, and the ( 110) peaks of the films were symmetrical. Fig. 4 shows the dependence of the crystallite size, (D), calculated by FWHM of the (ItO) peak of the X-ray diagrams and the (200) I ( 110) peak ratio on VA' When the films were deposited with the Ar-assisted process, and the conditionsRA = 1and RA =0.1 applied, (D) was increased incomparison with the Ar-assisted process. The (200)I ( 110) peak ratio had a minimum value at a VA value of 200 V when RA = I and at a value of VA of 400 V when RA =0.1. The
Vs" (110) 1800V j,.
1211)
:-, ... >
~ ----~:43
44
44
45
46
45 46
1200) (220)
! 20
40
60 80 29 (Deg.)
100
~(200)~ 120
Fig. 2. The X-ray diffraction patterns as a function ofthe sputtering-beam voltage. Vs.
20'
40
60
80
100
120
29 (Deg.)
Fig, 3.The X-ray diffraction patterns asa function ofthe Ar-assisted beam voltage. VA'
S./walsubo et al./ Thill Solid Fi/ms 28/-282 (/996)484-487
486
121""'1"'1''rn''-..,.............-.............-- 1000
RA-1 " 100 RA-O.l'
.
,0
8
10
'Ec
'oJ
~v
......
S'
0 CJ..
~
1
0. 4
~ m a.
&
". '0
"-, -0-'
~
2 0.01
0 100
1000
VA (V)
Fig. 4. Thedependence of thecrystallite size (of theX-ray diffraction) andthe (200) I ( 11 0) peak ratio on theAr-assisted voltage, VA'
bombardment energy of the Arions and an amount ofthe Ar icns changed the orientation ofthe crystallization inthe films. 3.2. Magnetic properties Fig. 5 shows the dependence of 4'1TMs and He for the Fe films when Vs isinthe range 300-1800 V. He was measured inthe direction of the hard axis, which was perpendicular to the incidence angle of the sputtering particles. The value of He drastically changed from 5 De to 35 De when Vs was varied inthe range 300-1800 V. He decreased monotonically as Vs increased until Vs was 1200 V. Considering the fact that the deposition rate was saturated at Vs above 1200 V, a large amount ofrecoiled Arwas generated inthe region above 1500 V.Therefore, He for the Fe films damaged by recoiled Ar, was increased. The 47TMs of the films had a minimum value of 16 kG at a Vs value of300 V. On the other hand, the 47TMs ofthe films for Vs values in the range 600-1800 V was about 2t'.5 kG, which isthe known saturation magnetization ofpure bulk Fe. The Fefilm prepared at a Vs value of 300 V contained about 20 atomic% carbon, according to results from ESCA and
O/S.
25
20
~
w
....
_
..
20
40
...... 15
~
30 Qi"
Q.
:E
u
:E
~
500
OO:RA=0.1
cr.. •.. , 10
d
'
Qi'
10
Q. 0
J:
't:J
5
• o
ell:A A- 1
II)
20 J:
10 5.0
20
_,_
15
0.0
25
50
C1l
~
RBS. This carbon came from the grids of the sputtering-ion sources. The usc of a low-energy beam, for example a Vs value of 300 V and a beam current of 50 rnA, was a heavy load for the Kaufman-type ion sources. InFefilms deposited when Vs values were in the range 600-1800 V, examination of the concentration of the impurities showed that there was carbon and oxygen (of several %, measured using ESCA) , and there was 0.02% Ar and 0.001% tungsten (measured using RBS). As a result of these properties, pure Fethin films with soft magnetic properties were prepared by maintaining values of the Vs of Ar at 1200 V. Therefore, in order to improve the magnetic properties, we investigated the relationship between the arrival rate ratio of Fe sputtered particles and that of Ar ions atthe surface ofthe growing thin films during deposition. Fe films were deposited when VA values were in the range ~o-2000 V, with the condition that the ratios of the arrival rate ofFeand Ar were J:I and 1:0.1, respectively. Fig. 6 shows the dependence of the values of 47TMs and He of the Fe films on the values of VA' when RA was 1 and O. I. In the case when RA was 1, the He of the films had a minimum value of 2.5 De at a VA value of 200 V. In the region when values of VA were in the range 80-200 V, the He ofthe films decreased as VA increased. Inthe region when VA was greater than 200 V, the He of the films increased as VA increased. In the case when RA was OJ, the He of the films had a value ofabout 2 Deat VA values above 400 V. In the region when VA values were in the range 80-400 V, the He of the films decreased as VA increased, and the increase was greater than that without the Ar-assisted process. In the region when VA was greater than 400 V, the He of the films was constant. On the other hand, the4'7TMs values ofthe films had a maximum value of 21.5 kG atthe points of maximum value of the (Ito) peak intensity. The proper energy of Ar ions necessary to obtain excellent soft magnetic films was shifted from 200 V to above 400 V by the Fe to Ar arrival rate. These results show that bombardment toobtain excellent
10
1000
1500
0 2000
Vs (V)
Fig. 5. The dependence of the saturation magnetization ' 47TM5' and the • • coerctvity, He. on thesputtering-beam voltage, Vs.
a
0
100
1000
VAM
Fig. ~ '. The dependence of the saturation magnetization, 47TMs• and the coercivity, He. on the Ar-assisted beam voltage. VA. when the Fe to Ar arrival rate ratios wereI:I (RA = 1) and 1:0.1 (R" =0.1).
S. lwatsubo !'t af./Thin Solid Films L8I-282 (1996) 484--487
soft magnetic films needed the proper amount and energy of Ar ions.
487
ity, including the orientation ofthe crystallization inthe films, and itreduced the movement resistance ofthe magnetic walls, thus enhancing the soft magnetic properties of Fe.
4. Conclusion
References
The films bombarded by Arions with proper kinetic energy at VA values in the range 200-400 V had a 47TMs value of 21.5 kG and a He value less than 2.5 De. Bombardment by the proper amount of Ar ions with moderate energy on the growing film surface improved the microscopic homogene-
[ 1] Y.K. Kim and M.Oliveria, J. Appl. Phys. 74(2) ( 1993) 1233. [2] M. Naoe, Y. Yamaga and N. Terada, IEEE Trans. Magll., MAG·21 (1985) 1900. [3J M. Naoe, N. Terada. Y. Hoshi and S. YamanaJca,IEE£ Tram. A..'1g/l., MAG·20(l984);p.1311 andp.1451.
Thin Solid Films 281-282 (1996) 484-487
Magnetic and structural properties of Fe films deposited by ion-beam sputtering with a high-energy assisted process S. Iwatsubo a.*, T. Takahashi b, M. Naoe
C
a Central
Research Institute, Toyama Industrial Technology Center, 150Futagami, Takaoka, Toyama 933, Japan h FaCility of Engineering, Toyama University, 3190 Gofuk», Toyama 930, Japan C Faculty a/Engineering. Tokyo Institute ofTeclmology, 2·/2·1, Osokayama, Meguro-ku. Tokyo 152, Japan
Abstract The microstructure and lhe magnetic properties of polycrystalline Fe films were investigated in detail by controlling the condition of the ion-beam sputtering with an Ar-assisted process, Fe films were deposited at a sputtering-beam voltage, Vs, in the range of 300-1800 V. The soft magnetic properties ofthe Fefilms significantly improved with increasing Vs, when the saturation magnetization, 47TMs' and thecoercivity, He, were 16-21.5 kG and 5 Oe, respectively. This improvement was caused bythe decrease of the crystallite size. Inorder to control the Fe crystallite size, Fe films were deposited when the Ar-assisted beam voltage, VA' was in the range of 80-2000 V, with the condition that the Ar to Fearrival ratios were I: 1 (RA = ) and 1:0.1 (RA =0.1). Fe films with excellent soft magnetic properties, such as 41t'Ms ofabout 21.5 kG and He of 2.5 Oe, were deposited on the substrate and bombarded bya VA of 200 V at R", :::: I and a VA of 400V at RA =0.1. The result implies that bombardment byArions, with the proper energy and flux, assists the improvement of the softmagnetic properties. Keywords: Iron; Sputtering; Ion bombardment; Magnetic properties and measurements
1. Introduction
Recently, it has been reported that Fe-based alloy films show excellent soft magnetic properties and high thermal stability, so they have attracted strong interesi for use as magnetic recording heads in high recording density applications. However, in the case of a thin film, their magnetic properties may be affected by a small amount of impurities contained iII the film [1]. According to reports on the preparation process of films or the purity of the Fe target, values of 47TM's and He can vary significantly. Therefore, it is necessary to control the film deposition parameters during preparation, in order to attain the soft magnetic properties. The ion-beam sputtering method isadequate for the above requirement [2,3]. Bombarding ions, with an Ar-assisted process, change the IDea! temperature on the film surface or damage the film. surface. In this study, the relationship between the magnetic and the structural properties and the size of the crystallites in the films has been investigated in detail bycontrolling theconditions ofthe ion-beam sputtering with a high-energy Ar-assisted process.
... Corresponding author. 0040-6090/96/$15.00 © 1996 Elsevier Science SA All rights reserved Pll S0040·6090( 96) 08680·4
2. Experiments
Fig. 1 shows theschematic diagram of the ion-beam sputtering apparatus used in this study. Specimen films were deposited onwater-cooled glass substrates byion-beam sput\
\ \~ as (Ar)
-
I
. .. ., Sputtering ionsource I Substrate holder ,, ',
- ,..~<, "~ \ ,
\
AI ion'..
~
I
,
v.s
\
\
~
..
~
'
I
".
,
/
,
.. - . / / \, \. .. /
~
~
/ ISubstnllc /
'
;;
I
I
:
:t ,
I
~
f
I I
;
~
:
I
'
' I !. I
, !~
,
I
I
. i .' .. : :
•
'
I
Ar ion
Electron
I
Neutralizer filament
I'
, Gasassisted ionsource Gas (Ar) Fig, I. A schematic diagram of the ion-beam sputtering apparatus with a gas-assisted ionsource.
485
S, lwarsubo et al./Thill Solid Films 28/-282 (/996) 484-487
tering from an Fe target of 99.9% purity. Both of the ion sources are Kaufman-type. The residual gas pressure in the chamber was 6 X 10- 5 Pa. Pure Argas was introduced asthe sputtering gas through the sputtering-ion source up to 3.6 X 10- 3 Pa, when the gas flow rate was 2 seem. Vs was controlled in the range 300-1800 V. The total sputteringbeam current was fixed at 50 rnA. For the At-assisted ion source, VA was varied in therange 80-2000 V. The current density of the assisted ions on the substrate surface was adjusted to0.49 and 0.049 A m- 2; these were calculated from the deposition rate (3.3 nm min - I) at Vs =1200V. The films thicknesses were 300-350 nm. The 47TMs and He values were measured by a vibrating sample magnetometer. The crystal structure was analyzed by X-ray diffractometry, and the composition of the films was measured by ESCA and RBS.
3. Results and discussion 3.1. Microstructure Fig. 2 shows 8-20 X-ray diffraction patterns of as-deposited Fe films as a function of the parameter, VS I in the range 300-1800 V. The films deposited at a Vs value of 300 V exhibited the sharpest diffraction peak, butthese films contain a large amount of carbon. Therefore, this case must be neglected when considering the relationship between the sputtering particles energy andthe microstructure. Except for the same case, broad X-fay diffraction peaks from the (110) planes and (200) planes of (X-Fe were observed. The peak intensity of the (200) plane showed a tendency to decrease as Vs increased. Thepeak intensity of the ( 110) plane had a minimum value at a Vs value of 1200 V. With an increase of Vs, there was a shift from a (200) orientation to a (110)
orientation. The ( 110) peaks above Vs values of900 V were not symmetrical, which suggests that the microstructure of the films was not homogeneous. Fig. 3 shows 8-20X-ray diffraction diagrams ofas-deposited Fe films as a function of the At-assisted beam voltage, VA' when the arrival ratio of Fe to Ar was 1: I. In Fig. 3, a value of 0 V for VA means that the film is deposited without an Ar-assisted process. For the. films deposited with the Arassisted process, the X-ray diffraction peaks from the (110), (211) and (220) planes of ·!X··Fe were observed. The peak intensity of the (200) plane from the films from the Arassisted process was very weak, On the other hand, the films deposited at VA values of 200 V have a maximum value at the (110) peak intensity. Moreover, the (220) peak, which is the half-lattice distance of the (110) plane, was only observed at VA valuer! of 200 V. Peak angles of the (1 to) plane in the films were constant at about 44.4 o. The (110) peaks of the films f..om the Ar-assisted process were symmetrical. These results show that the microstructure of the films was more homogeneous than without an Ar-assisted process, and the orientation of the crystallization in the films was controlled. In the films deposited with theAr-assisted process, and the condition that the ratio of the arrival rate of Fe to Ar was i:O.l, similar X-ray diffraction diagrams were observed. When VA was 400 V, the (110) peak intensity was at its maximum, and the ( 110) peaks of the films were symmetrical. Fig. 4 shows the dependence of the crystallite size, (D), calculated by FWHM of the (ItO) peak of the X-ray diagrams and the (200) I ( 110) peak ratio on VA' When the films were deposited with the Ar-assisted process, and the conditionsRA = 1and RA =0.1 applied, (D) was increased incomparison with the Ar-assisted process. The (200)I ( 110) peak ratio had a minimum value at a VA value of 200 V when RA = I and at a value of VA of 400 V when RA =0.1. The
Vs" (110) 1800V j,.
1211)
:-, ... >
~ ----~:43
44
44
45
46
45 46
1200) (220)
! 20
40
60 80 29 (Deg.)
100
~(200)~ 120
Fig. 2. The X-ray diffraction patterns as a function ofthe sputtering-beam voltage. Vs.
20'
40
60
80
100
120
29 (Deg.)
Fig, 3.The X-ray diffraction patterns asa function ofthe Ar-assisted beam voltage. VA'
S./walsubo et al./ Thill Solid Fi/ms 28/-282 (/996)484-487
486
121""'1"'1''rn''-..,.............-.............-- 1000
RA-1 " 100 RA-O.l'
.
,0
8
10
'Ec
'oJ
~v
......
S'
0 CJ..
~
1
0. 4
~ m a.
&
". '0
"-, -0-'
~
2 0.01
0 100
1000
VA (V)
Fig. 4. Thedependence of thecrystallite size
bombardment energy of the Arions and an amount ofthe Ar icns changed the orientation ofthe crystallization inthe films. 3.2. Magnetic properties Fig. 5 shows the dependence of 4'1TMs and He for the Fe films when Vs isinthe range 300-1800 V. He was measured inthe direction of the hard axis, which was perpendicular to the incidence angle of the sputtering particles. The value of He drastically changed from 5 De to 35 De when Vs was varied inthe range 300-1800 V. He decreased monotonically as Vs increased until Vs was 1200 V. Considering the fact that the deposition rate was saturated at Vs above 1200 V, a large amount ofrecoiled Arwas generated inthe region above 1500 V.Therefore, He for the Fe films damaged by recoiled Ar, was increased. The 47TMs of the films had a minimum value of 16 kG at a Vs value of300 V. On the other hand, the 47TMs ofthe films for Vs values in the range 600-1800 V was about 2t'.5 kG, which isthe known saturation magnetization ofpure bulk Fe. The Fefilm prepared at a Vs value of 300 V contained about 20 atomic% carbon, according to results from ESCA and
O/S.
25
20
~
w
....
_
..
20
40
...... 15
~
30 Qi"
Q.
:E
u
:E
~
500
OO:RA=0.1
cr.. •.. , 10
d
'
Qi'
10
Q. 0
J:
't:J
5
• o
ell:A A- 1
II)
20 J:
10 5.0
20
_,_
15
0.0
25
50
C1l
~
RBS. This carbon came from the grids of the sputtering-ion sources. The usc of a low-energy beam, for example a Vs value of 300 V and a beam current of 50 rnA, was a heavy load for the Kaufman-type ion sources. InFefilms deposited when Vs values were in the range 600-1800 V, examination of the concentration of the impurities showed that there was carbon and oxygen (of several %, measured using ESCA) , and there was 0.02% Ar and 0.001% tungsten (measured using RBS). As a result of these properties, pure Fethin films with soft magnetic properties were prepared by maintaining values of the Vs of Ar at 1200 V. Therefore, in order to improve the magnetic properties, we investigated the relationship between the arrival rate ratio of Fe sputtered particles and that of Ar ions atthe surface ofthe growing thin films during deposition. Fe films were deposited when VA values were in the range ~o-2000 V, with the condition that the ratios of the arrival rate ofFeand Ar were J:I and 1:0.1, respectively. Fig. 6 shows the dependence of the values of 47TMs and He of the Fe films on the values of VA' when RA was 1 and O. I. In the case when RA was 1, the He of the films had a minimum value of 2.5 De at a VA value of 200 V. In the region when values of VA were in the range 80-200 V, the He ofthe films decreased as VA increased. Inthe region when VA was greater than 200 V, the He of the films increased as VA increased. In the case when RA was OJ, the He of the films had a value ofabout 2 Deat VA values above 400 V. In the region when VA values were in the range 80-400 V, the He of the films decreased as VA increased, and the increase was greater than that without the Ar-assisted process. In the region when VA was greater than 400 V, the He of the films was constant. On the other hand, the4'7TMs values ofthe films had a maximum value of 21.5 kG atthe points of maximum value of the (Ito) peak intensity. The proper energy of Ar ions necessary to obtain excellent soft magnetic films was shifted from 200 V to above 400 V by the Fe to Ar arrival rate. These results show that bombardment toobtain excellent
10
1000
1500
0 2000
Vs (V)
Fig. 5. The dependence of the saturation magnetization ' 47TM5' and the • • coerctvity, He. on thesputtering-beam voltage, Vs.
a
0
100
1000
VAM
Fig. ~ '. The dependence of the saturation magnetization, 47TMs• and the coercivity, He. on the Ar-assisted beam voltage. VA. when the Fe to Ar arrival rate ratios wereI:I (RA = 1) and 1:0.1 (R" =0.1).
S. lwatsubo !'t af./Thin Solid Films L8I-282 (1996) 484--487
soft magnetic films needed the proper amount and energy of Ar ions.
487
ity, including the orientation ofthe crystallization inthe films, and itreduced the movement resistance ofthe magnetic walls, thus enhancing the soft magnetic properties of Fe.
4. Conclusion
References
The films bombarded by Arions with proper kinetic energy at VA values in the range 200-400 V had a 47TMs value of 21.5 kG and a He value less than 2.5 De. Bombardment by the proper amount of Ar ions with moderate energy on the growing film surface improved the microscopic homogene-
[ 1] Y.K. Kim and M.Oliveria, J. Appl. Phys. 74(2) ( 1993) 1233. [2] M. Naoe, Y. Yamaga and N. Terada, IEEE Trans. Magll., MAG·21 (1985) 1900. [3J M. Naoe, N. Terada. Y. Hoshi and S. YamanaJca,IEE£ Tram. A..'1g/l., MAG·20(l984);p.1311 andp.1451.