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Characteristics of electrolessly deposited cobalt tin phosphorus films
CQa me
i!B _-
ELSEVIER
Journal
of Magnetism
Characteristics
and Magnetic
Materials
A
journal of magnetism
A A
Efgnetic materials
134 (1994) 185-189
of electrolessly deposited cobalt tin phosphorus films H. Matsuda, 0. Takano
Department of Materials Science and Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji, Hyogo 671-22, Japan (Received
2 November
1993;
in revised form 24 January 1994)
Abstract An investigation has been made into the characteristics of electrolessly deposited cobalt tin phosphorus films. The codeposition of tin was found to have a significant effect on the coercivity of the films deposited from a high pH solution, notably increasing the maximum film coercivity and shifting the peak coercivity location within thicknesscoercivity curves. Further the addition of tin was found to decrease the weight loss in 5% NaCl solution by a factor of one eighth.
1. Introduction Electrolessly deposited cobalt phosphorus films have been studied extensively due to their potential for use in magnetic recording media [l-3]. To promote practical application of these films, demagnetization effects must be minimized and the coercivity in the th.in film region (100 nm) increased further. To optimize these properties, investigations have been carried out on electrolessly deposited cobalt phosphorus based alloys containing Ni [4], Zn [5], Mn [6], or W [7]. However, the corrosion of the magnetic layers remains a significant problem in such thin film devices, thus an improvement of the corrosion resistance of these films is also required. In electrodeposition studies, tin-cobalt binary alloy films with high corrosion resistance have been reported [8101. In electroless deposition, however, the characteristics of cobalt tin alloy films has received less attention. In this work, the effect of codeposition of tin on the corrosion resistance and magnetic proper-
ties of electrolessly deposited films has been studied.
cobalt phosphorus
2. Experimental An electroless cobalt phosphorus plating solution was used as a basic solution. The compositions and plating conditions of the solution are as follows: 50 mol me3 CoSO,, 200 mol m-3 NaH,PO,, 200 mol rnp3 Na,C,H,O,, 50 mol rnp3 Na,P,O, and 500 mol rnp3 H,BO,. The operating temperature was 353 f 1 K. The pH of the solution was fixed at either 7.0, 8.0 or 9.0 using a diluted NaOH solution. To prepare cobalt tin phosphorus films, sodium stannate was added to the solutions. Prior to the formation of full solution, sodium stannate was thoroughly stirred with complexing agents (Na,C,H,O,, Na,P,O,) in distilled water, in order to form stable tin complexes. Stirring proceeded for 24 hours. The solutions were prepared using pure grade reagents and distilled water. Prior to the formation of all
‘I
186
‘I I (1, ;
(I ii l
I( t , /
fqqrwri.\mand Magnetic Materials 134 (1994) 185-189
soh;iic)~~;, li+:l\.~.:;I (I!!’ l:r Ii 1: I’III;;~I~ ‘:I the disti 11:(l \” Itf:l. v!ij -illa ;el’l .I_ t II, ( I t wr. The op:t;~ in$! .~III~:I;I~ Ire :, I! CI:IIIU I : 11” h a watl.:r tl.ltl F’:~lye~h~ (:I ;: I(.I :I,hl;ll. tc i 1: _1:t of (thic.:8urc:d I: :lg an inrlwti ,I: 8:ollclled !j[ :ct:romctr:l~ 1SeiE;:l E1t::trolli.s :iPS plasrla 11001. Car osio1 rf:sz:.1Iice kc:15 e~;tlla c~i v~!!I an immcrs on tesl in 3 :;‘sk NaC: joluti311. ‘t’h: test was c:a.rrie( out in a I;(:: (lOOI ml) ilt t t, :iI:f:rature of X! 1 K.. The k :l:per; :ure w s (‘~:III:TI led with a wail r bath. 1%: : Late r)f ths: tin z :IIIS was deter,rnireci with tk a.iC of E3!;C141IJl,‘~‘!~1:l~~l’tIY, Model.ZL!i; 1. The cxrcivity ICI: fhe lr:lln; \\;I$ r-easured wit h t vibrating: :j831npl~:Inagr.~ei~)r.c:i~:~ (‘[‘oei Kogyo, WM-.3). Trallsmis:;i:ln c: e;: r :lrl microscop:/ ir ,estigation:j ‘>‘ere cxltried [WI: ~II :L JIZM 20001YL
3. Results
,I
nd disc:ux&
‘I
3.1, EZ!m cc,mpositi,:w
_______________
0
E’
. ..___-. ____- .- ._ .--
IO
(:3ncw:ralicbn of NZlUm s,t:rmate I rrd
m3
Fig. 1. Relation betwetzn :sO(lurn c,l;mnatc: ccln:e~~ ..Hiarl plating solutic~ns and alloy con:ent cr‘ tle]xb:iilc:~l‘ilrls.
0
0
100
200
300
Immersiontime I ks
Fig. 2. Relation between immersion time and weight loss of films.
case of films deposited from pH7 solution, the tin content increases slightly, and the phosphorus content fractionally decreases as the stannate concentration increases. In contrast, for the pH9 solution, the tin content reaches 9 mass% at a concentration of 20 mol 1-3 and the phosphorus content decreases from 5.5 to 2.3 mass%. The changes in the pH8 solution are between that of pH7 and pH9 solutions. It is found that the increase of tin content and the decrease of phosphorus content is dependent upon the pH of the solutions, notably at the higher pH solutions. Such trends have been reported in electroless cobalt zinc [51 and cobalt manganese [61 platings. 3.2. Corrosion resistance
!j
2:
13
1.6.-
in
The results of the immersion test for cobalt phosphorus and cobalt tin phosphorus films (5 km thick) deposited from pH9 solution are shown in Fig. 2. The results are plotted with immersion time as abscissa against weight loss per unit area (mg cme2) in 5% NaCl solution as ordinates. The weight loss of the films increases linearly as time proceeds and decreases as the tin content rises, with that for the 9% Sn film decreasing to oneeighth of that of the tin free film. It has been reported that electrodeposited CoSn films have a high corrosion resistance which originates in a surface layer which mainly consists of S&V) compounds [B,lll.
H. Matsuda, 0. Takano/Joumal 100
0
pH 7.0
OoR
A’ ‘; t5
‘E :g 8‘40 -+o@-j
I’
I-
I'
#ml I ~.--'L_b/ I / I r%' I, 01 6 . 0
0
I
CoSnP(0.4%Sn)
,CaSnP(O.t3v&n)
fJ&..
03
II ,I0 -L$ QO
wq
COP
0
a--w,
SO-
of Magnetism and Magnetic Materials 134 (1994) 185-189
coSnP(1.2%%)
I 22 G;, ‘,a,.;*-CD-_ ‘"..~_a$
L
100
200
300
490
3.3. Magnetic properties The thickness dependence of the magnetic properties of these films within the thin film region is critical for the potential application of electrolessly deposited cobalt phosphorus films as magnetic recording media. The effect of the addition of tin on the thickness dependence is shown in Figs. 3 and 4. For a solution of pH7 (Fig. 31, the coercivity of all the films peaks in the range 70-80 kAm_i at a thickness of 120 nm. No significant difference in behaviour is observed because the tin content of these films is low
0
100
200
486
484
482
1 D
Binding energy I eV
Film thickness I nm
Fig. 3. Film thickness dependence of coercivity in CoSnP films deposited from pH7 solutions.
0
488
300
Film thickness I nm
Fig. 4. Film thickness dependence of coercivity in CoSnP films deposited from pH9 solutions.
Fig. 5. ESCA spectra of electrolessly deposited CoSnP films.
(< 1.2 wt%). In contrast, for a solution of pH9 (Fig. 4), the coercivity of the cobalt phosphorus films is extremely low (under 1.0 kAn-‘1 and independent of film thickness. Significant changes in the thickness-coercivity curve, which comprise an increase of maximum coercivity and a shift in peak coercivity, are induced by the addition of tin. For 9% tin film, the maximum coercivity reaches 90 kArr_’ at a thickness of 60 nm. 3.4. ESCA As described, the codeposition of tin greatly influences the corrosion resistance and coercivity of cobalt tin phosphorus films. Consequently, it is of interest to determine the state of the tin atoms within the cobalt tin phosphorus film. The binding energy of a tin atom on 3d,,, orbit in a cobalt tin phosphorus films was investigated by ESCA as shown in Fig. 5. The figure shows the ESCA spectrum from films deposited from pH7 and pH9 solutions. In the case of the deposit from a pH7 solution, a sharp peak corresponding to the binding energy of Sn” is observed at 484.7 eV. For a pH9 solution, a broad peak is found around 487 eV, which is close to the binding energy of Sn(I1) or Sn(IV) (486.4 eV> rather than that of Sn” (484.7 eV>. From this result, it can be inferred that tin atoms in the films are in the state of valence 2 or 4, that is, the Sn is present in the form of oxide or hydroxide. As shown in Fig. 1,
188
I I
Mof\,rln.
(,
.’ ii;aii i
,I
Jo o 8 I, of Mr~grwrismand Magnetic Materials 134 (1994) 185-189
I: I in th. f’11nb\ .ie ~oc;le:d 1’:~n th: hi;;her it : x:r.r :; Illore prclx~‘~ e t i,.: hy.i x)-5&: is lorr~ecl 1,) 1nt: rcxtion bels,tz I t I IOII I ant C)H iors in thi: solutixx. Th: ,I) ut) I .i 01 :jn(C)H), in Iwater is as ttl: as 0.7 1;3 111 :at 2 ‘)3 K) antl it lherefor : m jy r:xist in th: fo: I of I ICOIoid II the sol It .ons. From tin :o
pH 5.I 111~ I, .S 11i:t~Lr. ‘!JhtrefSxe,
these lin’:.irgs, tllc coIloid>l tin hydre,, ide in high pH s )luticr (pF’>) 1s comidered to b: adsorbed onto the G11nsu11‘;1ceand 11c1~dedillt I tht fi.ms.
‘Fy:&:a1~:ramy 1~so-i coerc:ivily-thic:k nest trends for tt e film: are !;hown in Fig. 4. The structural fealu ‘I:!
(4 COP
pxt tern sh,Bws that the fihn is
camp Ised of‘ an amorphous structure, wh:J:h implies :h.at SLch filcls are superparam.~E nefc. This is tile cause of the extremely low coercivity in the tin fr:e films. Fig. 6(b) shc)ws micrograph for a cobal- tin pt:osphorus film. In this case, the film aprez rs to consi:#t.of grains with a di arleter 01’50 to ‘70 nm which i!, close to the criti :a1 dis.mc:ter for single domain particles in coba. t. The Elm, the:e:bre, s:~oulcl Exhibit a high coel’c vity. Independcmnt stL dies have confirmed that non-magnet:c materials, s lch as zinc hydrox de, segregatc:d at grain boundaries i educe ma g:letic: isolatior. of the grains, and corlsecluentl!r ead to an enhancemeni of coercivity [5]. In this study, it was imI:or,sible t :I cord.rm the presence of i:in hydroxide directly in a TEM observations. Hclwever, from the findings it is inlerred that the codeposited tin is present in the form of hydroxide and segregates at the grair. boundary. This may be thl: cause of ,the magnetic isolaticln and the reason for t:le rise in coercivity. In consic&ing the effect of the shift in the peak coercivity observed for codeposilion of tin, it can first IDenoted that an indepenlleni study
(b) CoSnP Fig. 6. Transmission electron micrographs deposited COP and CoSnP films.
of electrolessly
has suggested that crystallographic grains produced in electroless deposition grow as the film thickness increases with the rate of this growth dependent upon the film alloy content, in particular the phosphorus content [8]. It would therefore be interesting to reveal the cross-sectional structure at thick film regions. Unfortunately, this is difficult since films containing tin are too brittle for the preparation of cross-sectional specimens. However, from the findings in this work, it can be assumed that the grain growth rate increases with
H. Matsuda, 0. Takano/Joumal
of Magnetism and Magnetic Materials 134 (1994) 185-189
the reduction of phosphorus content, and consequently the single-domain particles with high coercivity emerge at the lower thickness region. This may be the reason for the shift in peak coercivity. Thus the coercivity trends are considered to be attributed to the specific codeposition behaviour of tin.
4. Conclusion The addition of tin to electrolessly deposited cobalt phosphorus films was found to have significant effects on the corrosion resistance and magnetic properties of the films. These effects are remarkable in high tin content films which are deposited from a higher pH (pH9) solution. The weight loss in 5% NaCl solution decreases to one-eighth by addition of 9 mass% tin to cobalt phosphorus films. Notable changes of magnetic properties, which comprise the increase of maximum coercivity and shift of peak coercivity in thickness-coercivity curves, were found in the films deposited from pH9 solution. The coercivity
189
trends are considered to result from the increase of grain size and magnetic isolation.
References [l] R.D. Fisher and W.H. Chilton, J. Electrochem. Sot. 109 (1962) 485. [2] D.E. Speliotis, J.R. Morrison and J.S. Judge, IEEE Trans. Magn. 4 (1965) 228. [3] H. Matsuda, 0. Takano, H. Gohuku and P.J. Grundy, J. Magn. Magn. Mater. 110 (1992) 227. [4] 0. Takano and H. Matsuda, Jpn. J. Met. Fin. 31 (1980) 146. [51 H. Matsuda and 0. Takano, J. Jpn Inst. Metals 52 (1988) 524. [61 H. Matsuda and 0. Takano, Trans. Electron. Inform. and Commun. Eng. 72C (1989) 24. [7] H. Matsuda, PhD Thesis, Himeji Inst., Tech. (1989) 28. [8] M. Clarke, R.G. Elbourne and C.A. Mackey, Trans. Inst. Met Fin. 50 (1972) 160. [9] V. Sree and T.L. Rama Char, Metalloberflache 15 (1961) 301. [lo] J.D.C. Hemsley and M.E. Roper, Trans. Inst. Met. Fin. 57 (1979) 77. [ill J.H. Thomas and S.P. Sharma, J. Vat. Sci. Tech. 15 (1978) 1706.
i!B _-
ELSEVIER
Journal
of Magnetism
Characteristics
and Magnetic
Materials
A
journal of magnetism
A A
Efgnetic materials
134 (1994) 185-189
of electrolessly deposited cobalt tin phosphorus films H. Matsuda, 0. Takano
Department of Materials Science and Engineering, Himeji Institute of Technology, 2167 Shosha, Himeji, Hyogo 671-22, Japan (Received
2 November
1993;
in revised form 24 January 1994)
Abstract An investigation has been made into the characteristics of electrolessly deposited cobalt tin phosphorus films. The codeposition of tin was found to have a significant effect on the coercivity of the films deposited from a high pH solution, notably increasing the maximum film coercivity and shifting the peak coercivity location within thicknesscoercivity curves. Further the addition of tin was found to decrease the weight loss in 5% NaCl solution by a factor of one eighth.
1. Introduction Electrolessly deposited cobalt phosphorus films have been studied extensively due to their potential for use in magnetic recording media [l-3]. To promote practical application of these films, demagnetization effects must be minimized and the coercivity in the th.in film region (100 nm) increased further. To optimize these properties, investigations have been carried out on electrolessly deposited cobalt phosphorus based alloys containing Ni [4], Zn [5], Mn [6], or W [7]. However, the corrosion of the magnetic layers remains a significant problem in such thin film devices, thus an improvement of the corrosion resistance of these films is also required. In electrodeposition studies, tin-cobalt binary alloy films with high corrosion resistance have been reported [8101. In electroless deposition, however, the characteristics of cobalt tin alloy films has received less attention. In this work, the effect of codeposition of tin on the corrosion resistance and magnetic proper-
ties of electrolessly deposited films has been studied.
cobalt phosphorus
2. Experimental An electroless cobalt phosphorus plating solution was used as a basic solution. The compositions and plating conditions of the solution are as follows: 50 mol me3 CoSO,, 200 mol m-3 NaH,PO,, 200 mol rnp3 Na,C,H,O,, 50 mol rnp3 Na,P,O, and 500 mol rnp3 H,BO,. The operating temperature was 353 f 1 K. The pH of the solution was fixed at either 7.0, 8.0 or 9.0 using a diluted NaOH solution. To prepare cobalt tin phosphorus films, sodium stannate was added to the solutions. Prior to the formation of full solution, sodium stannate was thoroughly stirred with complexing agents (Na,C,H,O,, Na,P,O,) in distilled water, in order to form stable tin complexes. Stirring proceeded for 24 hours. The solutions were prepared using pure grade reagents and distilled water. Prior to the formation of all
‘I
186
‘I I (1, ;
(I ii l
I( t , /
fqqrwri.\mand Magnetic Materials 134 (1994) 185-189
soh;iic)~~;, li+:l\.~.:;I (I!!’ l:r Ii 1: I’III;;~I~ ‘:I the disti 11:(l \” Itf:l. v!ij -illa ;el’l .I_ t II, ( I t wr. The op:t;~ in$! .~III~:I;I~ Ire :, I! CI:IIIU I : 11” h a watl.:r tl.ltl F’:~lye~h~ (:I ;: I(.I :I,hl;ll. tc i 1: _1:t of (thic.:
3. Results
,I
nd disc:ux&
‘I
3.1, EZ!m cc,mpositi,:w
_______________
0
E’
. ..___-. ____- .- ._ .--
IO
(:3ncw:ralicbn of NZlUm s,t:rmate I rrd
m3
Fig. 1. Relation betwetzn :sO(lurn c,l;mnatc: ccln:e~~ ..Hiarl plating solutic~ns and alloy con:ent cr‘ tle]xb:iilc:~l‘ilrls.
0
0
100
200
300
Immersiontime I ks
Fig. 2. Relation between immersion time and weight loss of films.
case of films deposited from pH7 solution, the tin content increases slightly, and the phosphorus content fractionally decreases as the stannate concentration increases. In contrast, for the pH9 solution, the tin content reaches 9 mass% at a concentration of 20 mol 1-3 and the phosphorus content decreases from 5.5 to 2.3 mass%. The changes in the pH8 solution are between that of pH7 and pH9 solutions. It is found that the increase of tin content and the decrease of phosphorus content is dependent upon the pH of the solutions, notably at the higher pH solutions. Such trends have been reported in electroless cobalt zinc [51 and cobalt manganese [61 platings. 3.2. Corrosion resistance
!j
2:
13
1.6.-
in
The results of the immersion test for cobalt phosphorus and cobalt tin phosphorus films (5 km thick) deposited from pH9 solution are shown in Fig. 2. The results are plotted with immersion time as abscissa against weight loss per unit area (mg cme2) in 5% NaCl solution as ordinates. The weight loss of the films increases linearly as time proceeds and decreases as the tin content rises, with that for the 9% Sn film decreasing to oneeighth of that of the tin free film. It has been reported that electrodeposited CoSn films have a high corrosion resistance which originates in a surface layer which mainly consists of S&V) compounds [B,lll.
H. Matsuda, 0. Takano/Joumal 100
0
pH 7.0
OoR
A’ ‘; t5
‘E :g 8‘40 -+o@-j
I’
I-
I'
#ml I ~.--'L_b/ I / I r%' I, 01 6 . 0
0
I
CoSnP(0.4%Sn)
,CaSnP(O.t3v&n)
fJ&..
03
II ,I0 -L$ QO
wq
COP
0
a--w,
SO-
of Magnetism and Magnetic Materials 134 (1994) 185-189
coSnP(1.2%%)
I 22 G;, ‘,a,.;*-CD-_ ‘"..~_a$
L
100
200
300
490
3.3. Magnetic properties The thickness dependence of the magnetic properties of these films within the thin film region is critical for the potential application of electrolessly deposited cobalt phosphorus films as magnetic recording media. The effect of the addition of tin on the thickness dependence is shown in Figs. 3 and 4. For a solution of pH7 (Fig. 31, the coercivity of all the films peaks in the range 70-80 kAm_i at a thickness of 120 nm. No significant difference in behaviour is observed because the tin content of these films is low
0
100
200
486
484
482
1 D
Binding energy I eV
Film thickness I nm
Fig. 3. Film thickness dependence of coercivity in CoSnP films deposited from pH7 solutions.
0
488
300
Film thickness I nm
Fig. 4. Film thickness dependence of coercivity in CoSnP films deposited from pH9 solutions.
Fig. 5. ESCA spectra of electrolessly deposited CoSnP films.
(< 1.2 wt%). In contrast, for a solution of pH9 (Fig. 4), the coercivity of the cobalt phosphorus films is extremely low (under 1.0 kAn-‘1 and independent of film thickness. Significant changes in the thickness-coercivity curve, which comprise an increase of maximum coercivity and a shift in peak coercivity, are induced by the addition of tin. For 9% tin film, the maximum coercivity reaches 90 kArr_’ at a thickness of 60 nm. 3.4. ESCA As described, the codeposition of tin greatly influences the corrosion resistance and coercivity of cobalt tin phosphorus films. Consequently, it is of interest to determine the state of the tin atoms within the cobalt tin phosphorus film. The binding energy of a tin atom on 3d,,, orbit in a cobalt tin phosphorus films was investigated by ESCA as shown in Fig. 5. The figure shows the ESCA spectrum from films deposited from pH7 and pH9 solutions. In the case of the deposit from a pH7 solution, a sharp peak corresponding to the binding energy of Sn” is observed at 484.7 eV. For a pH9 solution, a broad peak is found around 487 eV, which is close to the binding energy of Sn(I1) or Sn(IV) (486.4 eV> rather than that of Sn” (484.7 eV>. From this result, it can be inferred that tin atoms in the films are in the state of valence 2 or 4, that is, the Sn is present in the form of oxide or hydroxide. As shown in Fig. 1,
188
I I
Mof\,rln.
(,
.’ ii;aii i
,I
Jo o 8 I, of Mr~grwrismand Magnetic Materials 134 (1994) 185-189
I: I in th. f’11nb\ .ie ~oc;le:d 1’:~n th: hi;;her it : x:r.r :; Illore prclx~‘~ e t i,.: hy.i x)-5&: is lorr~ecl 1,) 1nt: rcxtion bels,tz I t I IOII I ant C)H iors in thi: solutixx. Th: ,I) ut) I .i 01 :jn(C)H), in Iwater is as ttl: as 0.7 1;3 111 :at 2 ‘)3 K) antl it lherefor : m jy r:xist in th: fo: I of I ICOIoid II the sol It .ons. From tin :o
pH 5.I 111~ I, .S 11i:t~Lr. ‘!JhtrefSxe,
these lin’:.irgs, tllc coIloid>l tin hydre,, ide in high pH s )luticr (pF’>) 1s comidered to b: adsorbed onto the G11nsu11‘;1ceand 11c1~dedillt I tht fi.ms.
‘Fy:&:a1~:ramy 1~so-i coerc:ivily-thic:k nest trends for tt e film: are !;hown in Fig. 4. The structural fealu ‘I:!
(4 COP
pxt tern sh,Bws that the fihn is
camp Ised of‘ an amorphous structure, wh:J:h implies :h.at SLch filcls are superparam.~E nefc. This is tile cause of the extremely low coercivity in the tin fr:e films. Fig. 6(b) shc)ws micrograph for a cobal- tin pt:osphorus film. In this case, the film aprez rs to consi:#t.of grains with a di arleter 01’50 to ‘70 nm which i!, close to the criti :a1 dis.mc:ter for single domain particles in coba. t. The Elm, the:e:bre, s:~oulcl Exhibit a high coel’c vity. Independcmnt stL dies have confirmed that non-magnet:c materials, s lch as zinc hydrox de, segregatc:d at grain boundaries i educe ma g:letic: isolatior. of the grains, and corlsecluentl!r ead to an enhancemeni of coercivity [5]. In this study, it was imI:or,sible t :I cord.rm the presence of i:in hydroxide directly in a TEM observations. Hclwever, from the findings it is inlerred that the codeposited tin is present in the form of hydroxide and segregates at the grair. boundary. This may be thl: cause of ,the magnetic isolaticln and the reason for t:le rise in coercivity. In consic&ing the effect of the shift in the peak coercivity observed for codeposilion of tin, it can first IDenoted that an indepenlleni study
(b) CoSnP Fig. 6. Transmission electron micrographs deposited COP and CoSnP films.
of electrolessly
has suggested that crystallographic grains produced in electroless deposition grow as the film thickness increases with the rate of this growth dependent upon the film alloy content, in particular the phosphorus content [8]. It would therefore be interesting to reveal the cross-sectional structure at thick film regions. Unfortunately, this is difficult since films containing tin are too brittle for the preparation of cross-sectional specimens. However, from the findings in this work, it can be assumed that the grain growth rate increases with
H. Matsuda, 0. Takano/Joumal
of Magnetism and Magnetic Materials 134 (1994) 185-189
the reduction of phosphorus content, and consequently the single-domain particles with high coercivity emerge at the lower thickness region. This may be the reason for the shift in peak coercivity. Thus the coercivity trends are considered to be attributed to the specific codeposition behaviour of tin.
4. Conclusion The addition of tin to electrolessly deposited cobalt phosphorus films was found to have significant effects on the corrosion resistance and magnetic properties of the films. These effects are remarkable in high tin content films which are deposited from a higher pH (pH9) solution. The weight loss in 5% NaCl solution decreases to one-eighth by addition of 9 mass% tin to cobalt phosphorus films. Notable changes of magnetic properties, which comprise the increase of maximum coercivity and shift of peak coercivity in thickness-coercivity curves, were found in the films deposited from pH9 solution. The coercivity
189
trends are considered to result from the increase of grain size and magnetic isolation.
References [l] R.D. Fisher and W.H. Chilton, J. Electrochem. Sot. 109 (1962) 485. [2] D.E. Speliotis, J.R. Morrison and J.S. Judge, IEEE Trans. Magn. 4 (1965) 228. [3] H. Matsuda, 0. Takano, H. Gohuku and P.J. Grundy, J. Magn. Magn. Mater. 110 (1992) 227. [4] 0. Takano and H. Matsuda, Jpn. J. Met. Fin. 31 (1980) 146. [51 H. Matsuda and 0. Takano, J. Jpn Inst. Metals 52 (1988) 524. [61 H. Matsuda and 0. Takano, Trans. Electron. Inform. and Commun. Eng. 72C (1989) 24. [7] H. Matsuda, PhD Thesis, Himeji Inst., Tech. (1989) 28. [8] M. Clarke, R.G. Elbourne and C.A. Mackey, Trans. Inst. Met Fin. 50 (1972) 160. [9] V. Sree and T.L. Rama Char, Metalloberflache 15 (1961) 301. [lo] J.D.C. Hemsley and M.E. Roper, Trans. Inst. Met. Fin. 57 (1979) 77. [ill J.H. Thomas and S.P. Sharma, J. Vat. Sci. Tech. 15 (1978) 1706.