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Characteristic of electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy
Journal of Magnetism and Magnetic Materials 128 (1993) 386-390 North-Holland
Characteristics of electrolessly deposited CoReNiMnP with perpendicular magnetic anisotropy H. Matsuda
a~*, 0. Takano
a, P.J. Grundy
films
b
a Himeji Institute of Technology, Department of Materials Science and Engineering, 2167 Shosha, Himeji, Hyogo, 671-22, Japan ’ Department of Physics, University of Salford, Salford M5 4wT, UK
Received 22 April 1993; in revised form 28 June 1993
Electrolessly deposited CoReNiMnP films, which have been developed for perpendicular magnetic recording media, exhibit the characteristics of both incoherent and wall motion mechanisms. Thinner films ( < 80 nm) mainly consist of elements with a wall motion model, whilst a incoherent rotational model is dominant in thicker films. The absence of perpendicular magnetic anisotropy in thinner films could be due to the randomly (poorly) oriented initial layer.
1. Introduction We have already developed an electrolessly deposited CoReNiMnP film which has the capacity of a promising medium for perpendicular magnetic recording [l]. However, for its practical application, the film has a problem that the perpendicular magnetic anisotropy decreases at small thickness (< 500 nm) [2]. The details of the relation between the magnetic properties and microstructure of the films with different thickness is therefore of particular interest. It has been reported that the measurement of the angular dependence of a hysteresis loop can serve as a determination of the switching mechanism [3]. The method has been applied to sputtered CoCr films [4-71. In this study, we introduce the method to reveal the switching mechanism in the CoReNiMnP films, and discuss the relationship between the mechanism and structural anisotropy.
2. Experimental Polyimide sheet (of thickness 25 pm) was used as substrate material. Because catalytic activity is * Corresponding author. 0304-8853/93/$06.00
essential for the initiation of the deposition, sputtered palladium nuclei were previously deposited on one side of the sheet. The solution contents and conditions for the CoReNiMnP film are as follows: 60 mol rnv3 CoSO,, 40 mol rnv3 NiSO,, 30 mol me3 MnSO,, 0 to 20 mol me3 (variable) NH,ReO,, 200 mol me3 NaH,PO,, 500 mol me3 Na,C,H,O, and 500 mol me3 (NH,),SO,. The operating temperature was 323 K. The pH was adjusted with NH,OH. A series of Co alloy films of Co,_,Re,Ni,,Mn,P, compositions (0
0 1993 - Elsevier Science Publishers B.V. All rights reserved
H. Matsuda et aL / Electrolessly deposited CoReNiMnPfilms with perpendicular magnetic anisotropy
c-axis. The dispersion was evaluated by the half width value of the rocking curve of the (002) Bragg peak [9].
8O
3. Results and discussion
Fig. 1 shows the magnetic properties of an electrolessly deposited Co30Re30Ni35MnEP 3 film as a function of film thickness. As shown in the figure, H c ± and H k decrease linearly with thickness below 500 nm, and it is almost independent of thickness above 500 nm. In these curves, a fairly clear " k n e e " can be found at a thickness of 500 rim. The result signifies that a fall of perpendicular magnetic anisotropy occur in the initial layer. In order to reveal the cause for the low coercivity below the knee thickness, the angular dependence of hysteresis loops was investigated for Co30Re30Ni35MnEP 3 films with different thickness. Fig. 2 (a) shows the angular dependence of hysteresis loops for a Co30Rea0NiasMn2P 3 film with thickness of 500 nm. No compensation for demagnetization is made to the loops. When the field is applied perpendicular to the film plane (/2--0°), the loop exhibits a sheared due to the demagnetizing field. Correction for this field for a continuous film or "sheet" produces a good rectangular loop. The angular dependence of hysteresis loops of 150 nm thick films is shown in Fig. 2(b). The coercivity gradually decreases as the angle 12 increases. Fig. 3 exhibits the angular dependence of coercivity for Co3oRe3oNi35Mn2P3 films with different film thickness. In the case of thicker films (t = 700, 500 nm), the maximum value is shown at 0 °, and then decreases almost linearly with the increase o f / 2 . For the thinnest film (t -- 50 nm), the coercivity value is almost independent of the angle, which may indicate that the film is an isotropic one. For the thinner films (t = 80, 150 nm), the coercivity increases in the low angle region (/2 < 30°). The change settles to a constant value for / / > 45 °. The result for these films is similar to the case of thin CoCr films which compares well with a model for a wall motion mechanism (dashed line) [6,7].
J - HG(J~,..,.,,,O
I
5OO
//--
2C
a0oT, -i-
-m
Coad:leaoNbsMnaPa film
500
387
1000
1500
2000
100 <
2500
Rim thickness / nm Fig. 1. F i l m t h i c k n e s s d e p e n d e n c e o f c o e r c i v i t y H c ± .
Fig. 4 shows the angular dependence of the normalized hysteresis loss for Co30Re30Ni35 Mn2P 3 films. In the case of thicker films (t = 500, 700 nm), the loss decreases linearly. The result agrees approximately with the theoretical angular dependence for the rotational model (dashed line) which is assumed by Tanaka et al. [7]. The data from the thinner films (t = 80, 50 nm) agree closely with the theoretical line (double dashed line) for the wall motion model [7]. From the results in Fig. 4, it can be seen that there is a critical difference between 150 and 80 nm thick films. From Figs. 3 and 4, the magnetization reversal mechanism for thicker films (t -- 500, 700 nm) can be identified as that of incoherent rotation and for films less than 80 nm in thickness domain wall motion appears to be dominant. In the medium range of 150 to 500 nm, the films exhibit mixed characteristics of both models. From these findings, it is inferred that a rotational layer with perpendicular anisotropy emerges at a thickness of 150 nm and that the wall motion layer gives way to a rotational layer at the thickness region between 150 and 500 nm. Beyond 500 nm thick, the rotational layer is dominant. In Fig. 5, the thicknesses at which the rotational layer starts are plotted against Re content. The thickness will hereinafter be abbreviated to 'TRL' For lower Re films (Re < 10%), no TRL is observed. In the case of Co45Re~sNi35Mn2P 3 film,
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy
388
M/Ms M/Ms
~ = .o" (1)
o.oo.
~
o°(//)
-8oo /
kAm"I
o = go'(//)
'
800 H app{ / kAm'~
(b)
(a) Film thickness = 500 nm
Film thickness = 150 nm
Fig. 2. (a) Hysteresis loops of a C o R e N i M n P film with 500 n m thickness in directions of various angles from the film normal. (b) Hysteresis loops of a C o R e N i M n P film with 150 n m thickness in directions of various angles from the film normal.
1.0 . . . . . .
"7
E
o
0.8'
i
O.8--
.~,
£
Wall motion - . .
.
.____%',
.
I
.
t
x: 0.4 o Z
0.2
0
0 (i)
15
I
30
45
1
60
0
"15
Angle /deg.
Fig. 3. Angular dependence of the coercivity H c ±.
90 (//)
,
0 (±)
15
30
45
,
60
75
1
90 (,'/)
AngJe / d e g
Fig. 4. Angular dependence of normalized hysteresis loss.
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy 500
'
400
~
C°~x iRixNi35Mn2P3"
C
"
.J
~- 200 100
10
0
0
20
30
40
Rhenium / wt% Fig. 5. E f f e c t of the R e c o n t e n t on TRL.
a rotational layer emerges at a thickness of 500 nm. TRL shifts to a lower thickness with the increase of rhenium content. Above a rhenium content of 30%, the change settles at a constant value of 150 nm. Fig. 6 shows the relation between film thickness and A050 in the C060_xRexNi35Mn2P 3 films. In each curve, a 'knee' is observable. AO50 decreases linearly with the increase of thickness below the knee thickness. Above this thickness, the values are almost constant. For C030Re30
20
16.
~
12
--••
C'°60"xRexNi35Mi~2P3 x=Recontent ~
0
0
1 500
Ni35Mn2P 3 film, the knee thickness in this figure coincides with the knee thickness in Hc-thickness curve (Fig. 1). From these results, it is inferred that randomly oriented crystallites exist near the interface of the CoReNiMnP/substrate and that they decrease the coercivity of the films. In sputtered films which exhibit perpendicular magnetic anisotropy, similar results have been reported [10,11], that is, the thinner CoCr sputtered films show considerable in-plane orientation of the caxis (large A050) and low coercivity. Further information from Fig. 6 is that the 'knee' shifts to a lower thickness with the increase of the Re content. A similar tendency is shown in the rhenium content dependence of TRL in Fig. 5. The absolute value does not coincide with each other between TRL (Fig. 5) and the knee thickness in Fig. 6, that is, for Co30Re30Ni35MnzP3 film, TRL is 150 nm in Fig. 5, whilst the knee is observable at 500 nm in Fig. 6. However, the rhenium content dependence qualitatively corresponds in each case. In collating these results, it is suggested that perpendicular anisotropic layers grow onto the initial layers, that the thickness of the initial layer depends on the rhenium content of the films and that the fall of perpendicular magnetic anisotropy at the initial layer could be due to the randomly (poorly) oriented crystallites.
4. Conclusion
-
x=30"-0"
389
1000
1500
2000
Film thickness I nm Fig. 6. F i l m t h i c k n e s s d e p e n d e n c e of A050.
2500
Electrolessly deposited CoReNiMnP films exhibit the characteristics of both incoherent and wall motion mechanisms. Thinner films ( < 80 nm) mainly consist of the elements with a wall motion model, whilst a incoherent rotational model is dominant in thicker films. A knee thickness between the above two layers with different magnetic properties is observable in both magnetic measurements and X-ray observations. The knee thickness shifts to a lower thickness with increase of rhenium content. The loss of perpendicular magnetic anisotropy in the initial layer could be due to the random crystallographic orientation.
390
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy
Acknowledgements This work has been supported financially by the Hosokawa Powder Technology Foundation. The authors would like to extend their gratitude to the Foundation.
References [1] H. Matsuda, O. Takano and P.J. Grundy, J. Magn. Magn. Mater. 128 (1993) 381 (this issue). [2] H. Izumitani, M.Sc. Thesis, Himeji Institute of Technology (1985) 56.
[3] K. Ouchi and S. Iwasaki, IECEJ Tech. Group Meeting on Magnetic Recording, Jpn., MR76-3 (1976). [4] S. Iwasaki, K. Ouchi and N. Honda, IEEE Trans. Magn. 16 (1980) 1111. [5] C. Barbero, IEEE Trans. Magn. 18 (1982) 1104. [6] S. Honda, T. Yamakawa and T. Kusuda, IEEE Trans. Magn. 21 (1985) 1468. [7] T. Tanaka, K. Ouchi and S. Iwasaki, J. Mag. Soc. Jpn. 10 (1986) 65. [8] H. Matsuda and O. Takano, J. Appl. Electrochemistry 23 (1993) 183. [9] K. Ouchi and S. Iwasaki, Ann. Conf. Inst. Electronics, Information and Communication Engineers Jpn. (1980) 1-197. [10] T.M. Coughlin, IEEE Trans. Magn. 17 (1981) 3169. [11] T. Wielinga, IEEE Trans. Magn. 17 (1981) 3178.
Characteristics of electrolessly deposited CoReNiMnP with perpendicular magnetic anisotropy H. Matsuda
a~*, 0. Takano
a, P.J. Grundy
films
b
a Himeji Institute of Technology, Department of Materials Science and Engineering, 2167 Shosha, Himeji, Hyogo, 671-22, Japan ’ Department of Physics, University of Salford, Salford M5 4wT, UK
Received 22 April 1993; in revised form 28 June 1993
Electrolessly deposited CoReNiMnP films, which have been developed for perpendicular magnetic recording media, exhibit the characteristics of both incoherent and wall motion mechanisms. Thinner films ( < 80 nm) mainly consist of elements with a wall motion model, whilst a incoherent rotational model is dominant in thicker films. The absence of perpendicular magnetic anisotropy in thinner films could be due to the randomly (poorly) oriented initial layer.
1. Introduction We have already developed an electrolessly deposited CoReNiMnP film which has the capacity of a promising medium for perpendicular magnetic recording [l]. However, for its practical application, the film has a problem that the perpendicular magnetic anisotropy decreases at small thickness (< 500 nm) [2]. The details of the relation between the magnetic properties and microstructure of the films with different thickness is therefore of particular interest. It has been reported that the measurement of the angular dependence of a hysteresis loop can serve as a determination of the switching mechanism [3]. The method has been applied to sputtered CoCr films [4-71. In this study, we introduce the method to reveal the switching mechanism in the CoReNiMnP films, and discuss the relationship between the mechanism and structural anisotropy.
2. Experimental Polyimide sheet (of thickness 25 pm) was used as substrate material. Because catalytic activity is * Corresponding author. 0304-8853/93/$06.00
essential for the initiation of the deposition, sputtered palladium nuclei were previously deposited on one side of the sheet. The solution contents and conditions for the CoReNiMnP film are as follows: 60 mol rnv3 CoSO,, 40 mol rnv3 NiSO,, 30 mol me3 MnSO,, 0 to 20 mol me3 (variable) NH,ReO,, 200 mol me3 NaH,PO,, 500 mol me3 Na,C,H,O, and 500 mol me3 (NH,),SO,. The operating temperature was 323 K. The pH was adjusted with NH,OH. A series of Co alloy films of Co,_,Re,Ni,,Mn,P, compositions (0
0 1993 - Elsevier Science Publishers B.V. All rights reserved
H. Matsuda et aL / Electrolessly deposited CoReNiMnPfilms with perpendicular magnetic anisotropy
c-axis. The dispersion was evaluated by the half width value of the rocking curve of the (002) Bragg peak [9].
8O
3. Results and discussion
Fig. 1 shows the magnetic properties of an electrolessly deposited Co30Re30Ni35MnEP 3 film as a function of film thickness. As shown in the figure, H c ± and H k decrease linearly with thickness below 500 nm, and it is almost independent of thickness above 500 nm. In these curves, a fairly clear " k n e e " can be found at a thickness of 500 rim. The result signifies that a fall of perpendicular magnetic anisotropy occur in the initial layer. In order to reveal the cause for the low coercivity below the knee thickness, the angular dependence of hysteresis loops was investigated for Co30Re30Ni35MnEP 3 films with different thickness. Fig. 2 (a) shows the angular dependence of hysteresis loops for a Co30Rea0NiasMn2P 3 film with thickness of 500 nm. No compensation for demagnetization is made to the loops. When the field is applied perpendicular to the film plane (/2--0°), the loop exhibits a sheared due to the demagnetizing field. Correction for this field for a continuous film or "sheet" produces a good rectangular loop. The angular dependence of hysteresis loops of 150 nm thick films is shown in Fig. 2(b). The coercivity gradually decreases as the angle 12 increases. Fig. 3 exhibits the angular dependence of coercivity for Co3oRe3oNi35Mn2P3 films with different film thickness. In the case of thicker films (t = 700, 500 nm), the maximum value is shown at 0 °, and then decreases almost linearly with the increase o f / 2 . For the thinnest film (t -- 50 nm), the coercivity value is almost independent of the angle, which may indicate that the film is an isotropic one. For the thinner films (t = 80, 150 nm), the coercivity increases in the low angle region (/2 < 30°). The change settles to a constant value for / / > 45 °. The result for these films is similar to the case of thin CoCr films which compares well with a model for a wall motion mechanism (dashed line) [6,7].
J - HG(J~,..,.,,,O
I
5OO
//--
2C
a0oT, -i-
-m
Coad:leaoNbsMnaPa film
500
387
1000
1500
2000
100 <
2500
Rim thickness / nm Fig. 1. F i l m t h i c k n e s s d e p e n d e n c e o f c o e r c i v i t y H c ± .
Fig. 4 shows the angular dependence of the normalized hysteresis loss for Co30Re30Ni35 Mn2P 3 films. In the case of thicker films (t = 500, 700 nm), the loss decreases linearly. The result agrees approximately with the theoretical angular dependence for the rotational model (dashed line) which is assumed by Tanaka et al. [7]. The data from the thinner films (t = 80, 50 nm) agree closely with the theoretical line (double dashed line) for the wall motion model [7]. From the results in Fig. 4, it can be seen that there is a critical difference between 150 and 80 nm thick films. From Figs. 3 and 4, the magnetization reversal mechanism for thicker films (t -- 500, 700 nm) can be identified as that of incoherent rotation and for films less than 80 nm in thickness domain wall motion appears to be dominant. In the medium range of 150 to 500 nm, the films exhibit mixed characteristics of both models. From these findings, it is inferred that a rotational layer with perpendicular anisotropy emerges at a thickness of 150 nm and that the wall motion layer gives way to a rotational layer at the thickness region between 150 and 500 nm. Beyond 500 nm thick, the rotational layer is dominant. In Fig. 5, the thicknesses at which the rotational layer starts are plotted against Re content. The thickness will hereinafter be abbreviated to 'TRL' For lower Re films (Re < 10%), no TRL is observed. In the case of Co45Re~sNi35Mn2P 3 film,
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy
388
M/Ms M/Ms
~ = .o" (1)
o.oo.
~
o°(//)
-8oo /
kAm"I
o = go'(//)
'
800 H app{ / kAm'~
(b)
(a) Film thickness = 500 nm
Film thickness = 150 nm
Fig. 2. (a) Hysteresis loops of a C o R e N i M n P film with 500 n m thickness in directions of various angles from the film normal. (b) Hysteresis loops of a C o R e N i M n P film with 150 n m thickness in directions of various angles from the film normal.
1.0 . . . . . .
"7
E
o
0.8'
i
O.8--
.~,
£
Wall motion - . .
.
.____%',
.
I
.
t
x: 0.4 o Z
0.2
0
0 (i)
15
I
30
45
1
60
0
"15
Angle /deg.
Fig. 3. Angular dependence of the coercivity H c ±.
90 (//)
,
0 (±)
15
30
45
,
60
75
1
90 (,'/)
AngJe / d e g
Fig. 4. Angular dependence of normalized hysteresis loss.
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy 500
'
400
~
C°~x iRixNi35Mn2P3"
C
"
.J
~- 200 100
10
0
0
20
30
40
Rhenium / wt% Fig. 5. E f f e c t of the R e c o n t e n t on TRL.
a rotational layer emerges at a thickness of 500 nm. TRL shifts to a lower thickness with the increase of rhenium content. Above a rhenium content of 30%, the change settles at a constant value of 150 nm. Fig. 6 shows the relation between film thickness and A050 in the C060_xRexNi35Mn2P 3 films. In each curve, a 'knee' is observable. AO50 decreases linearly with the increase of thickness below the knee thickness. Above this thickness, the values are almost constant. For C030Re30
20
16.
~
12
--••
C'°60"xRexNi35Mi~2P3 x=Recontent ~
0
0
1 500
Ni35Mn2P 3 film, the knee thickness in this figure coincides with the knee thickness in Hc-thickness curve (Fig. 1). From these results, it is inferred that randomly oriented crystallites exist near the interface of the CoReNiMnP/substrate and that they decrease the coercivity of the films. In sputtered films which exhibit perpendicular magnetic anisotropy, similar results have been reported [10,11], that is, the thinner CoCr sputtered films show considerable in-plane orientation of the caxis (large A050) and low coercivity. Further information from Fig. 6 is that the 'knee' shifts to a lower thickness with the increase of the Re content. A similar tendency is shown in the rhenium content dependence of TRL in Fig. 5. The absolute value does not coincide with each other between TRL (Fig. 5) and the knee thickness in Fig. 6, that is, for Co30Re30Ni35MnzP3 film, TRL is 150 nm in Fig. 5, whilst the knee is observable at 500 nm in Fig. 6. However, the rhenium content dependence qualitatively corresponds in each case. In collating these results, it is suggested that perpendicular anisotropic layers grow onto the initial layers, that the thickness of the initial layer depends on the rhenium content of the films and that the fall of perpendicular magnetic anisotropy at the initial layer could be due to the randomly (poorly) oriented crystallites.
4. Conclusion
-
x=30"-0"
389
1000
1500
2000
Film thickness I nm Fig. 6. F i l m t h i c k n e s s d e p e n d e n c e of A050.
2500
Electrolessly deposited CoReNiMnP films exhibit the characteristics of both incoherent and wall motion mechanisms. Thinner films ( < 80 nm) mainly consist of the elements with a wall motion model, whilst a incoherent rotational model is dominant in thicker films. A knee thickness between the above two layers with different magnetic properties is observable in both magnetic measurements and X-ray observations. The knee thickness shifts to a lower thickness with increase of rhenium content. The loss of perpendicular magnetic anisotropy in the initial layer could be due to the random crystallographic orientation.
390
H. Matsuda et al. / Electrolessly deposited CoReNiMnP films with perpendicular magnetic anisotropy
Acknowledgements This work has been supported financially by the Hosokawa Powder Technology Foundation. The authors would like to extend their gratitude to the Foundation.
References [1] H. Matsuda, O. Takano and P.J. Grundy, J. Magn. Magn. Mater. 128 (1993) 381 (this issue). [2] H. Izumitani, M.Sc. Thesis, Himeji Institute of Technology (1985) 56.
[3] K. Ouchi and S. Iwasaki, IECEJ Tech. Group Meeting on Magnetic Recording, Jpn., MR76-3 (1976). [4] S. Iwasaki, K. Ouchi and N. Honda, IEEE Trans. Magn. 16 (1980) 1111. [5] C. Barbero, IEEE Trans. Magn. 18 (1982) 1104. [6] S. Honda, T. Yamakawa and T. Kusuda, IEEE Trans. Magn. 21 (1985) 1468. [7] T. Tanaka, K. Ouchi and S. Iwasaki, J. Mag. Soc. Jpn. 10 (1986) 65. [8] H. Matsuda and O. Takano, J. Appl. Electrochemistry 23 (1993) 183. [9] K. Ouchi and S. Iwasaki, Ann. Conf. Inst. Electronics, Information and Communication Engineers Jpn. (1980) 1-197. [10] T.M. Coughlin, IEEE Trans. Magn. 17 (1981) 3169. [11] T. Wielinga, IEEE Trans. Magn. 17 (1981) 3178.