- Email: [email protected]
Si(111) substrates
Journalol maonotlsm and magnetic
~
Journal of Magnetism and Magnetic Materials 156 (1996) 375-376
,~
ELSEVIER
m~erlals
Giant magnetoresistance of Co/Cu, NiFeCo/Cu, and NiFe/Cu multilayers sputter-deposited on Cu/Si(111) substrates Kyeong-Ik Min a,*, Seung-Ki Joo a, Kyung-Ho Shin b " Department of Metallurgical Engineering, Seoul National University, San 56-1 Shinlim-Dong Kwanak-Gu, Seoul, South Korea b Magnetic Thin Film Laborato~, Korea Institute of Science and Technology. Cheongryang, Seoul. South Korea
Abstract Magnetoresistance values of 33%, 19%, and 12% were observed at the second magnetoresistance maximum peaks for C o / C u , NiFeCo/Cu and N i F e / C u multilayers, respectively. Magnetoresistance was rather insensitive to the thickness of Cu spacer layer. In-plane uniaxial magnetic anisotropy was found in these multilayers. (110) pseudo-epitaxial growth of these multilayers rendered one of the Si(110) an easy axis in the plane. In recent years, multilayers exhibiting giant magnetoresistance have received great attention due to potential for magnetic device application. Giant magnetoresistance has been known to be extremely sensitive to the substrate material [1] and underlayers [1,2] mainly because the antiferromagnetic coupling of adjacent ferromagnetic layers across the spacer layer is greatly dependent on the multilayeredness and crystallographic orientation of the multilayer [2]. It has recently been reported [3] that Cu works very well as an underlayer for N i F e / C u multilayer grown on Si(ll 1) substrates. In this paper, large magnetoresistance, uniaxial magnetic anisotropy, and pseudo-epitaxial growth of C o / C u , NiFeCo/Cu, and N i F e / C u multilayers are investigated. C o / C u , Ni66Fe16Co18/Cu , and Ni81Fel9/Cu multilayers were prepared by rf-magnetron sputtering on Cu(50 A ) / S i ( l l l ) substrates where the S i [ l l l ] axis was off orientation by 4 ° from the surface normal toward the Si[110] axis. R - H curves were measured at room temperature by applying the external magnetic field along the easy and hard axes to study the anisotropy of magnetization behavior. The texture and crystallography of the films were studied by X-ray diffraction analysis using a wide-angle X-ray diffractometer and by TEM analysis using a Philips C M 3 0 / S T E M electron microscol~e. Magnetoresistance (MR) of [Co(20 A)/Cu(t~u "~)]20, [NiFeCo(20 ,~/Cu(tc, ~')]2o, and [NiFe(20 A)]~o multilayers as a function of Cu thickness is plotted in Fig. I. It can be seen from this figure that MR is rather insensitive to Cu thickness, relative to previous reports [1,4,5]. It was found that these multilayers had large
volume (80%) of antiferromagnetically coupled phase [6]. Under optimized sample preparation condition, 33%, 19%, and 12% MR could be obtained in [Co(30 A)/Cu(23 '~)]~0, [NiFeCo(20 ,~)/Cu(21 '~)],o, and [NiFe(20 ,~)/YCu(22 "~)]2o samples, respectively.-Magnetoresistance was also relatively insensitive to the thickness of magnetic layer, as can be seen in Fig. 2. In the case of C o / C u SoYStem, MR was nearly constant in the thickness range 15 A to 30 A. It has been reported that MR shows a maximum at ~ 15 ~, and rapidly decreases as the magnetic layer thickness increases. This result is different from a previous report [7]. Uniaxial magnetic anisotropy was found in the film plane for C o / C u , NiFeCo/Cu, and N i F e / C u multilayers. Easy axis and hard axis R - H curves for [Co(30 A)/Cu(23 ~k)]20, [NiFeCo(20 ,~)/Cu(23 ,~)1~o, and [NiFe(30 ,~)/Cu(23 '~)]lo samples are shown in Fig. 3. Anisotropy fields estimated from Fig. 3 are ~ 1000 Oe, ~ 400 Oe, 40
30 A
Fax:
+ 82-2-958-5409; email:
A
A
Co/Cu
o
NiFeCo/Cu
E2
NiFe/Cu A A
(%)2o 15 10
0
0
0
0
0
~-I3
O
El
2'3
2'4
5 0
2'1
2'2
2'~
2'6
Cu thickness (,~)
Fig. 1. Dependence of MR on Cu thickness in [Co(20 ,~)/Cu(tco ,~)]2o, [NiFeCo(20 ~t)/Cu(tcu '~)]2o, and [NiFe(20 A)/Cu(tc~ , •~)]1(i multilayers.
0304-8853/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 03114-885 3(95 )00905- 1
ZX
MR25
A/Cu(tco
* Corresponding author. minky @kistmail.kist.re.kr.
,x
35
376
K.-L Min et al. / Journal of Magnetism and Magnetic Materials 156 (1996) 375-376 ,
.
,
•
,
•
,
.
35 30
,
.
,
--~-- Co/Ca o NiFeColCu
,,-__
25 MR
(%) 20
/
15
"~
~t, - - u - - NiFe/Cu ~,,,__ __,,
,~-----
/ ~ - o ~ O - - o - - - - - =
,/
10
0
~ O ~ ~ o
Oj
0
2'0
1'0
2'5
3'0
tMag (/~ )
Fig. 2. Dependence of MR on the thickness of magnetic layers in [Co(tco A/Cu(23 "~)]2 [NiFeCO(tNiFeCoA)/Cu(23 "~)]2o and [NiFe(tNiF¢ A)/Cu(23 A)]t0 multilayers. and ~ 200 Oe for C o / C u , NiFeCo/Cu, and N i F e / C u multilayers, respectively. These values are of reasonable magnitude when the origin of the magnetic anisotropy is magnetocrystalline. The easy axis and hard axis were along the S i ( l l 0 ) axis and the S i ( l l 2 ) axis in the film plane, respectively, suggesting an epitaxial growth of Cu on the misorientated S i ( l l l ) substrate. Fig. 4 shows a TEM micrograph of [NiFe(20 ,~)/Cu(24 -~)]2o sample. In this figure, the image shows polycrystalline feature but grains were not clearly defined. Electron diffraction pattern along the [110] zone axis of Cu and NiFe is shown in the inset to Fig. 4, suggesting a pseudo-epitaxial [110] growth of N i F e / C u on Si(ll 1). It should be mentioned that no
~ ' ~
(a)
25
20 ~
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lo[-
elo
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--e-- easyaxis
t •
0
^
0 F oooooooooo01A***~lk*dLA***%l@oooooooooo o5 !
= , = , -2000-1500-1000
=
,
i , -500
= 0
,
= 500
,
i 1000
,
= 1500
,
= 2000
Fig. 4. A TEM micrograph of [NiFe(20 ,~)/Cu(24 ,~]2o sample. The inset to the bright field image shows the electron diffraction pattern along the [110] zone axis of Cu and NiFe. crystalline signal could be observed in X-ray diffraction spectra. For more information on the mechanism of the pseudo-epitaxial growth, a cross-sectional HREM study is underway and the result will be published elsewhere. It seems from Figs. 3 and 4 that the uniaxial magnetic anisotropy might originate from the pseudo-epitaxial growth of the multilayers. The insensitiveness of MR to the Cu and Co thicknesses is not clear at this time. Although it is likely to be related to the [110] growth of the film, more work is required since the Full Width at Half Maximum of the MR peak with respect to the spacer layer thickness for the C o / C u multilayer shown in Fig. 1 is above 5 ,~ and is far greater than that for the (110) sandwich samples grown by MBE [8]. Acknowledgements: We are very grateful to Dr. K. Park for his help and advice on TEM analysis. This work was financially supported by Korea Telecom Research Center and also by Research Center for Thin Film Fabrication and Crystal Growing of Advanced Materials. References
oooo, -1000-800 10/I 8
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. . . . . . . . . . . -800
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200
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Field (Oe) Fig. 3. R - H curves of [Co(30 A/Cu(23 ~-)]2o (a), [NiFeCo(20 •~)/Cu(23 A]2o (b), and [NiFe(30 ,~)/Cu(23 A)]]0 multilayers (c). The easy axis and hard axis were along the Si(ll0) and Si(112) axes in the film plane, respectively.
[1] D.H. Mosca, F. Petroff, A. Fert, P.A. Schroeder, W.P. Pratt Jr., and R. Laloee, J. Magn. Magn. Mater. 94 (1991) L1. [2] S.S.P. Parkin, Z.G. Li and D.J. Smith, Appl. Phys. Lett. 58 (1991) 2710. [3] K.-I. Min and S.-K. Joo, Technical report of IEICE (1994-11) MR94-49. [4] M. Jimbo, S. Tsunashima, T. Kanda, S. Goto and S. Uchiyama, J. Appl. Phys. (1993) 3341. [5] R. Nakatani, T. Dei and Y. Sugita, J. Appl. Phys. 73 (1993) 6375. [6] K.-I. Min and S.-K. Joo, Paper presented at MML'95, Cambridge, UK (Sept. 1995), No. MM-0231. [7] D.M. Edwards, J. Mathon, R.B. Muniz and S.S.P. Parkin, J. Magn. Magn. Mater. 114 (1992) 252. [8] M.T. Johnson, R. Coehoorn, J.J. de Vries, N.W.E. McGee, J. aan de Stegge and P.J.H. Bloemen, Phys. Rev. Lett. 69 (1992) 969.
~
Journal of Magnetism and Magnetic Materials 156 (1996) 375-376
,~
ELSEVIER
m~erlals
Giant magnetoresistance of Co/Cu, NiFeCo/Cu, and NiFe/Cu multilayers sputter-deposited on Cu/Si(111) substrates Kyeong-Ik Min a,*, Seung-Ki Joo a, Kyung-Ho Shin b " Department of Metallurgical Engineering, Seoul National University, San 56-1 Shinlim-Dong Kwanak-Gu, Seoul, South Korea b Magnetic Thin Film Laborato~, Korea Institute of Science and Technology. Cheongryang, Seoul. South Korea
Abstract Magnetoresistance values of 33%, 19%, and 12% were observed at the second magnetoresistance maximum peaks for C o / C u , NiFeCo/Cu and N i F e / C u multilayers, respectively. Magnetoresistance was rather insensitive to the thickness of Cu spacer layer. In-plane uniaxial magnetic anisotropy was found in these multilayers. (110) pseudo-epitaxial growth of these multilayers rendered one of the Si(110) an easy axis in the plane. In recent years, multilayers exhibiting giant magnetoresistance have received great attention due to potential for magnetic device application. Giant magnetoresistance has been known to be extremely sensitive to the substrate material [1] and underlayers [1,2] mainly because the antiferromagnetic coupling of adjacent ferromagnetic layers across the spacer layer is greatly dependent on the multilayeredness and crystallographic orientation of the multilayer [2]. It has recently been reported [3] that Cu works very well as an underlayer for N i F e / C u multilayer grown on Si(ll 1) substrates. In this paper, large magnetoresistance, uniaxial magnetic anisotropy, and pseudo-epitaxial growth of C o / C u , NiFeCo/Cu, and N i F e / C u multilayers are investigated. C o / C u , Ni66Fe16Co18/Cu , and Ni81Fel9/Cu multilayers were prepared by rf-magnetron sputtering on Cu(50 A ) / S i ( l l l ) substrates where the S i [ l l l ] axis was off orientation by 4 ° from the surface normal toward the Si[110] axis. R - H curves were measured at room temperature by applying the external magnetic field along the easy and hard axes to study the anisotropy of magnetization behavior. The texture and crystallography of the films were studied by X-ray diffraction analysis using a wide-angle X-ray diffractometer and by TEM analysis using a Philips C M 3 0 / S T E M electron microscol~e. Magnetoresistance (MR) of [Co(20 A)/Cu(t~u "~)]20, [NiFeCo(20 ,~/Cu(tc, ~')]2o, and [NiFe(20 A)]~o multilayers as a function of Cu thickness is plotted in Fig. I. It can be seen from this figure that MR is rather insensitive to Cu thickness, relative to previous reports [1,4,5]. It was found that these multilayers had large
volume (80%) of antiferromagnetically coupled phase [6]. Under optimized sample preparation condition, 33%, 19%, and 12% MR could be obtained in [Co(30 A)/Cu(23 '~)]~0, [NiFeCo(20 ,~)/Cu(21 '~)],o, and [NiFe(20 ,~)/YCu(22 "~)]2o samples, respectively.-Magnetoresistance was also relatively insensitive to the thickness of magnetic layer, as can be seen in Fig. 2. In the case of C o / C u SoYStem, MR was nearly constant in the thickness range 15 A to 30 A. It has been reported that MR shows a maximum at ~ 15 ~, and rapidly decreases as the magnetic layer thickness increases. This result is different from a previous report [7]. Uniaxial magnetic anisotropy was found in the film plane for C o / C u , NiFeCo/Cu, and N i F e / C u multilayers. Easy axis and hard axis R - H curves for [Co(30 A)/Cu(23 ~k)]20, [NiFeCo(20 ,~)/Cu(23 ,~)1~o, and [NiFe(30 ,~)/Cu(23 '~)]lo samples are shown in Fig. 3. Anisotropy fields estimated from Fig. 3 are ~ 1000 Oe, ~ 400 Oe, 40
30 A
Fax:
+ 82-2-958-5409; email:
A
A
Co/Cu
o
NiFeCo/Cu
E2
NiFe/Cu A A
(%)2o 15 10
0
0
0
0
0
~-I3
O
El
2'3
2'4
5 0
2'1
2'2
2'~
2'6
Cu thickness (,~)
Fig. 1. Dependence of MR on Cu thickness in [Co(20 ,~)/Cu(tco ,~)]2o, [NiFeCo(20 ~t)/Cu(tcu '~)]2o, and [NiFe(20 A)/Cu(tc~ , •~)]1(i multilayers.
0304-8853/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 03114-885 3(95 )00905- 1
ZX
MR25
A/Cu(tco
* Corresponding author. minky @kistmail.kist.re.kr.
,x
35
376
K.-L Min et al. / Journal of Magnetism and Magnetic Materials 156 (1996) 375-376 ,
.
,
•
,
•
,
.
35 30
,
.
,
--~-- Co/Ca o NiFeColCu
,,-__
25 MR
(%) 20
/
15
"~
~t, - - u - - NiFe/Cu ~,,,__ __,,
,~-----
/ ~ - o ~ O - - o - - - - - =
,/
10
0
~ O ~ ~ o
Oj
0
2'0
1'0
2'5
3'0
tMag (/~ )
Fig. 2. Dependence of MR on the thickness of magnetic layers in [Co(tco A/Cu(23 "~)]2 [NiFeCO(tNiFeCoA)/Cu(23 "~)]2o and [NiFe(tNiF¢ A)/Cu(23 A)]t0 multilayers. and ~ 200 Oe for C o / C u , NiFeCo/Cu, and N i F e / C u multilayers, respectively. These values are of reasonable magnitude when the origin of the magnetic anisotropy is magnetocrystalline. The easy axis and hard axis were along the S i ( l l 0 ) axis and the S i ( l l 2 ) axis in the film plane, respectively, suggesting an epitaxial growth of Cu on the misorientated S i ( l l l ) substrate. Fig. 4 shows a TEM micrograph of [NiFe(20 ,~)/Cu(24 -~)]2o sample. In this figure, the image shows polycrystalline feature but grains were not clearly defined. Electron diffraction pattern along the [110] zone axis of Cu and NiFe is shown in the inset to Fig. 4, suggesting a pseudo-epitaxial [110] growth of N i F e / C u on Si(ll 1). It should be mentioned that no
~ ' ~
(a)
25
20 ~
co/cn
/ JLA" AL \
,.'o °~ o~ o o
? o ./, I O
lo[-
elo
Io • ~
o o ^00
5~
--e-- easyaxis
t •
0
^
0 F oooooooooo01A***~lk*dLA***%l@oooooooooo o5 !
= , = , -2000-1500-1000
=
,
i , -500
= 0
,
= 500
,
i 1000
,
= 1500
,
= 2000
Fig. 4. A TEM micrograph of [NiFe(20 ,~)/Cu(24 ,~]2o sample. The inset to the bright field image shows the electron diffraction pattern along the [110] zone axis of Cu and NiFe. crystalline signal could be observed in X-ray diffraction spectra. For more information on the mechanism of the pseudo-epitaxial growth, a cross-sectional HREM study is underway and the result will be published elsewhere. It seems from Figs. 3 and 4 that the uniaxial magnetic anisotropy might originate from the pseudo-epitaxial growth of the multilayers. The insensitiveness of MR to the Cu and Co thicknesses is not clear at this time. Although it is likely to be related to the [110] growth of the film, more work is required since the Full Width at Half Maximum of the MR peak with respect to the spacer layer thickness for the C o / C u multilayer shown in Fig. 1 is above 5 ,~ and is far greater than that for the (110) sandwich samples grown by MBE [8]. Acknowledgements: We are very grateful to Dr. K. Park for his help and advice on TEM analysis. This work was financially supported by Korea Telecom Research Center and also by Research Center for Thin Film Fabrication and Crystal Growing of Advanced Materials. References
oooo, -1000-800 10/I 8
'
. . . . . . . . . . . -800
"
'
-400 "
-200
0
200
"
'
"
'
(C) /
-300
'
600 "
'
J
i
-2b0'-100
800 "
1000] '
NiFe/Cu
~
//~; ~ I ~
0
,oooo 400
,
"~ L
6
--easy a x i s --o-- ham axis •
"~\
i
100' 2~0
i
300
Field (Oe) Fig. 3. R - H curves of [Co(30 A/Cu(23 ~-)]2o (a), [NiFeCo(20 •~)/Cu(23 A]2o (b), and [NiFe(30 ,~)/Cu(23 A)]]0 multilayers (c). The easy axis and hard axis were along the Si(ll0) and Si(112) axes in the film plane, respectively.
[1] D.H. Mosca, F. Petroff, A. Fert, P.A. Schroeder, W.P. Pratt Jr., and R. Laloee, J. Magn. Magn. Mater. 94 (1991) L1. [2] S.S.P. Parkin, Z.G. Li and D.J. Smith, Appl. Phys. Lett. 58 (1991) 2710. [3] K.-I. Min and S.-K. Joo, Technical report of IEICE (1994-11) MR94-49. [4] M. Jimbo, S. Tsunashima, T. Kanda, S. Goto and S. Uchiyama, J. Appl. Phys. (1993) 3341. [5] R. Nakatani, T. Dei and Y. Sugita, J. Appl. Phys. 73 (1993) 6375. [6] K.-I. Min and S.-K. Joo, Paper presented at MML'95, Cambridge, UK (Sept. 1995), No. MM-0231. [7] D.M. Edwards, J. Mathon, R.B. Muniz and S.S.P. Parkin, J. Magn. Magn. Mater. 114 (1992) 252. [8] M.T. Johnson, R. Coehoorn, J.J. de Vries, N.W.E. McGee, J. aan de Stegge and P.J.H. Bloemen, Phys. Rev. Lett. 69 (1992) 969.