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Magnetic properties of R2Co17−xGax compounds (RSm and Gd)
ELSEVIER
Journal
of Alloys
and Compounds
259
( 1997) 65-68
dleton’, E. Briickb, F.R. de “hstitrcte of Metul Research. Chirtese Sciences Academy, 110015. Shxyang. P.R. China hVtrrl der Whds-Zeernan Institute. University of Amsterdam, Valckenierstraot 6.5, 1018 XE Amsterdam. The Netherlmds
‘Philips Research
kuborato~.
Pro& HoIstlam
4. 5656 AA Eindhoven.
The Netherlands
Received 4 February 1997; accepted 1I February 1997
Abstract The magnetic magnetic
properties
measurements
concentration
of R2Co,,
and X-ray
,Ga,
leads to a sign reversal
concentration
to easy-axis anisotropy
Co-sublattice
anisotropy
in both series.
0
at relatively
1997 Elsevier
with
OZL
on magnetically
aligned
of !he magnetocrystalline
for higher Ga concentration.
add constructively.
domain walls, in particular
compounds
diffraction
In the Sm,Co ,,
high Ga concentrations.
for R=Sm
The measurements anisotropy
from
,Ga, compounds,
of considerable
were studied
have shown
easy-plane
the Sm-sublattice
magnetic
Science S.A. ,&I,: Sm,Co,,
,Ga,: Magnetic properties
structure corresponds to the rhombo Inlcrmetallic
compounds of the type R,Co,,
formed
befwcen rare earth metals (R) and cobalt are of consideriibk
tcchnologicnl imd fundamcnti\l inkrest
surprising the
is the MiWior
stitution
of the
Co
01’ nr)n-mi~gnL’tic A
OSl
[ I ,2).
ompounds in which for CO
Il!iKlS
IO
iI
in the chaructcr of the Co-
blatrice anisotropy. Recent studies have shown that particulnrly interesting phenomena are observed in R,Co, 7 compounds in which there is a competition between the R- and Co-sublattice udy, we have extended these studies to
2. Gd,Co,,
_ ,Ga,
compounds .Y 55
compounds with x=0, arc melting
and Sm,Co,,__ ,Ga,
I, 3, 5, 6 and 7 were prepared by lea
*Corresponding author.
09258388/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PII SO925-8388(97)00104-7
YPe. e ~~~~~neti~li~e~suretne~ts wcrc etometer in
the
by means of
that increasing
anisotropy
hardness and the oc There is a strong decrease of the Curie temperature wi
Rare earth cobnIt compounds;Gallium substitution;Gd,Co,,
Keywrds:
Co-sublattice
This leads to materials
and O5x57
powders.
for
anisotropy
Ga
low and the
nce of narrow a concentration
66
2
J
4
5
6
7
f3
absence of an external field, was mcasurcd with increasirlg t~~~9l~~r~~tl~r~. The M(T) curves are characterized in a11 cases by II ~~~t~9~9~~r~itiv~ly low VillW of the tnagnctization in the rature range, followed by il stroirg increase at ~)i99chigt9cr td’mf9criltlirh3, Such bel9avior was not observed. l9owever, if the Silllll3lCN were fiel4l~~o(~l~~~ Itll:tlSCIT~tll~tIltS, Rrlslllts (~t~t~~ii9~~1 witl9 ill9tl lrlcl with .\ =5 Ci119Ix compared with ii9Of tl9O~~l~(~~~~i~l(~~lS ~~et9~~vi~)r of tlae t~~99~~r~~tur~ Jepet9det9cc of’ the ln~~~~~ti~~~tio~ we t99~~is~lr~d the hystere2s loops of ~er~-field-~~~) the compound wittr .Y =5 at various te les of such n9easurements are shown in nch9ce of the coercivity is displayed in
The
Some of these positions contribute positively to the magnetocrystalline anisotropy of the Co sublattice, others negatively. It follows from the results of our investigation of the Gd,,Co,,_ ,Ga, compounds that the Co sublattice anisotropy changes its sign from negative to positive with increasing Ga concentration. This may be partly the result of a preferential substitution of the Ga atoms into the Co sites that contribute negatively to the Co-sublattice anisocalculations tropy. However, electronic-band-structure made on ihe structurally related YCo, compound, showed that quite large changes of the magnetocrystalline anisotropy are expected for comparatively small shifts of the Fermi energy [6]. It is possible that a similar situation applies also to the presently considered R2Col, compounds, meaning that the sign change in anisotropy energy cell change ira band can also be thz result o nts able to provide structure. Neutron-diffra experimental information on the preferential site occupation by Ga in R,Co,,_ ,Ga, compounds are planned in the near future. It follows from the results given in Section 3 that all Sm,Co,, _,Ga, compounds have uniaxiai anisotropy that increases in magnitude with increasing Ga concentration due to the fact that the Co-sublattice anisotropy also becomes uniaxial in character. The results presented for the x-5 compound furthermore show that these materials possess an intrinsic coercivity that is strongly temperature dependent and determines for a large part the tel~~~er~~t~re dependence of the magnetization when the latter is measured in external fields comparable to or lower than the ctrercivity. intrinsic coercivity caia most ermb of’narrow dOrl9ilil9 Walls omain walls m expected wI9enever 119~’ bcconres OSthe same order of magnitude y* Such conditions arc ed it9 the StnzCo,7 _ ,Ga, systen9 when a concentration. because the increase of nergy is accompanied by a decrease in Curie tem~rature or exchange energy. T thickness can become of the order of few interatomic
urie te~99~er~~tur~ is seen
9ere cy is a cot9 ve been observe ,Co, 7 is the presence of
67
a . c
a . m
. 9 pOH=0.05T * .
. : e . .
1
y,H=0.05 T
0
300
600
900
1200
1500
0
300
600
T(K)
I
Sm,Col,Ga6
we have plotted the data in Fig. 4 in the form of a semi-logarithmic plot (left scale) also. These results are quite convincmg in revealing the thermally activated nature of the domain-wall motion. It Sollows from the results shown in intrinsic coercivity is very low at room te
tial. c,>ncentration fluctuations may occur in the solidsolution system Sm,Co ,7_ ,Ga,. The conditio
900
1200
1500
.
,. .*... ... .+.. 4.
:
*.
.’
9‘
.?
. : :
20K
. , *.* * ; )
??
*.
..*’
6QK
120K
: : ,....‘,..,..,:t.‘:
.‘a
:
__.__-L-1
0
1
-1
0
1
-1
1
0
I+(T)
K. StrnaI. in: Handbook of ;kumognek Wohlfitrth
snd
Ic)t(H.p.
Amhtcrdiml, R.J.
K.H.J.
Rildwim&i
Himdhooh of
Ru~chow
Magnetic Materials. E.P.
(Ed5.1 Vol.
4.
Nonh
Holland.
I 3I
and I.J.M.
Mapneric
Franhe. in:
blilIerl:ll\,
K.H.J.
Buschow.
North Holland. Amsterdam
(Ed.).
IW3.
Vol. 7. p, 3oi. <‘.I I. de (iroot. F.R. dc Boer. K.I I.J. Buachow. %. Hu. W.B. Y&n. Alloy5 Camp. 33
J.
( I‘~OO) lxx.
(‘.I I. de (iroca. l”.R. dc Bosr ilntl K.I 1.J. IJt~\chow. l’hjsicii
13(111
prcvd. (i..l.
I.ou~!.
(i.K.
Milri\\l1\~1\~, S Ml\hril. O.A. I’rmglc. %,
YCl\Ul, 11.1’. Mltltlll~lO~l, I’lrys.
(i.tl.0.
K
I I .I
I3ll~~‘llOM, I’. (~lUltl)Cilll.
I Irl, W.H. .I
AlIpl.
70 ( I?)%1) 5.38 1, I)ili~ltkr~~~~.I?J. Kelly. M.Ia.1I. S~hm~rlmltl\. l’hy\. Rev. I! 5.i
( I ‘Ml ) I ‘bl I 5 171tl. tli~rbar;~ C‘. Btick. R. Lallairc. I). I-‘iIcc;lrtl. J. Phy\. 32 ( I07 1) 200. IHI I’. k$mli. C.D. Graham. J. Appl. Phys. 42 ( IO7 I ) I209. 1’4 J.J. van don Broek. H. %ijl\tra. IEEE Trans. Map. MiIg. 231.
S~l~pl Cl
7
( IO71 )
Journal
of Alloys
and Compounds
259
( 1997) 65-68
dleton’, E. Briickb, F.R. de “hstitrcte of Metul Research. Chirtese Sciences Academy, 110015. Shxyang. P.R. China hVtrrl der Whds-Zeernan Institute. University of Amsterdam, Valckenierstraot 6.5, 1018 XE Amsterdam. The Netherlmds
‘Philips Research
kuborato~.
Pro& HoIstlam
4. 5656 AA Eindhoven.
The Netherlands
Received 4 February 1997; accepted 1I February 1997
Abstract The magnetic magnetic
properties
measurements
concentration
of R2Co,,
and X-ray
,Ga,
leads to a sign reversal
concentration
to easy-axis anisotropy
Co-sublattice
anisotropy
in both series.
0
at relatively
1997 Elsevier
with
OZL
on magnetically
aligned
of !he magnetocrystalline
for higher Ga concentration.
add constructively.
domain walls, in particular
compounds
diffraction
In the Sm,Co ,,
high Ga concentrations.
for R=Sm
The measurements anisotropy
from
,Ga, compounds,
of considerable
were studied
have shown
easy-plane
the Sm-sublattice
magnetic
Science S.A. ,&I,: Sm,Co,,
,Ga,: Magnetic properties
structure corresponds to the rhombo Inlcrmetallic
compounds of the type R,Co,,
formed
befwcen rare earth metals (R) and cobalt are of consideriibk
tcchnologicnl imd fundamcnti\l inkrest
surprising the
is the MiWior
stitution
of the
Co
01’ nr)n-mi~gnL’tic A
OSl
[ I ,2).
ompounds in which for CO
Il!iKlS
IO
iI
in the chaructcr of the Co-
blatrice anisotropy. Recent studies have shown that particulnrly interesting phenomena are observed in R,Co, 7 compounds in which there is a competition between the R- and Co-sublattice udy, we have extended these studies to
2. Gd,Co,,
_ ,Ga,
compounds .Y 55
compounds with x=0, arc melting
and Sm,Co,,__ ,Ga,
I, 3, 5, 6 and 7 were prepared by lea
*Corresponding author.
09258388/97/$17.00 0 1997 Elsevier Science S.A. All rights reserved. PII SO925-8388(97)00104-7
YPe. e ~~~~~neti~li~e~suretne~ts wcrc etometer in
the
by means of
that increasing
anisotropy
hardness and the oc There is a strong decrease of the Curie temperature wi
Rare earth cobnIt compounds;Gallium substitution;Gd,Co,,
Keywrds:
Co-sublattice
This leads to materials
and O5x57
powders.
for
anisotropy
Ga
low and the
nce of narrow a concentration
66
2
J
4
5
6
7
f3
absence of an external field, was mcasurcd with increasirlg t~~~9l~~r~~tl~r~. The M(T) curves are characterized in a11 cases by II ~~~t~9~9~~r~itiv~ly low VillW of the tnagnctization in the rature range, followed by il stroirg increase at ~)i99chigt9cr td’mf9criltlirh3, Such bel9avior was not observed. l9owever, if the Silllll3lCN were fiel4l~~o(~l~~~ Itll:tlSCIT~tll~tIltS, Rrlslllts (~t~t~~ii9~~1 witl9 ill9tl lrlcl with .\ =5 Ci119Ix compared with ii9Of tl9O~~l~(~~~~i~l(~~lS ~~et9~~vi~)r of tlae t~~99~~r~~tur~ Jepet9det9cc of’ the ln~~~~~ti~~~tio~ we t99~~is~lr~d the hystere2s loops of ~er~-field-~~~) the compound wittr .Y =5 at various te les of such n9easurements are shown in nch9ce of the coercivity is displayed in
The
Some of these positions contribute positively to the magnetocrystalline anisotropy of the Co sublattice, others negatively. It follows from the results of our investigation of the Gd,,Co,,_ ,Ga, compounds that the Co sublattice anisotropy changes its sign from negative to positive with increasing Ga concentration. This may be partly the result of a preferential substitution of the Ga atoms into the Co sites that contribute negatively to the Co-sublattice anisocalculations tropy. However, electronic-band-structure made on ihe structurally related YCo, compound, showed that quite large changes of the magnetocrystalline anisotropy are expected for comparatively small shifts of the Fermi energy [6]. It is possible that a similar situation applies also to the presently considered R2Col, compounds, meaning that the sign change in anisotropy energy cell change ira band can also be thz result o nts able to provide structure. Neutron-diffra experimental information on the preferential site occupation by Ga in R,Co,,_ ,Ga, compounds are planned in the near future. It follows from the results given in Section 3 that all Sm,Co,, _,Ga, compounds have uniaxiai anisotropy that increases in magnitude with increasing Ga concentration due to the fact that the Co-sublattice anisotropy also becomes uniaxial in character. The results presented for the x-5 compound furthermore show that these materials possess an intrinsic coercivity that is strongly temperature dependent and determines for a large part the tel~~~er~~t~re dependence of the magnetization when the latter is measured in external fields comparable to or lower than the ctrercivity. intrinsic coercivity caia most ermb of’narrow dOrl9ilil9 Walls omain walls m expected wI9enever 119~’ bcconres OSthe same order of magnitude y* Such conditions arc ed it9 the StnzCo,7 _ ,Ga, systen9 when a concentration. because the increase of nergy is accompanied by a decrease in Curie tem~rature or exchange energy. T thickness can become of the order of few interatomic
urie te~99~er~~tur~ is seen
9ere cy is a cot9 ve been observe ,Co, 7 is the presence of
67
a . c
a . m
. 9 pOH=0.05T * .
. : e . .
1
y,H=0.05 T
0
300
600
900
1200
1500
0
300
600
T(K)
I
Sm,Col,Ga6
we have plotted the data in Fig. 4 in the form of a semi-logarithmic plot (left scale) also. These results are quite convincmg in revealing the thermally activated nature of the domain-wall motion. It Sollows from the results shown in intrinsic coercivity is very low at room te
tial. c,>ncentration fluctuations may occur in the solidsolution system Sm,Co ,7_ ,Ga,. The conditio
900
1200
1500
.
,. .*... ... .+.. 4.
:
*.
.’
9‘
.?
. : :
20K
. , *.* * ; )
??
*.
..*’
6QK
120K
: : ,....‘,..,..,:t.‘:
.‘a
:
__.__-L-1
0
1
-1
0
1
-1
1
0
I+(T)
K. StrnaI. in: Handbook of ;kumognek Wohlfitrth
snd
Ic)t(H.p.
Amhtcrdiml, R.J.
K.H.J.
Rildwim&i
Himdhooh of
Ru~chow
Magnetic Materials. E.P.
(Ed5.1 Vol.
4.
Nonh
Holland.
I 3I
and I.J.M.
Mapneric
Franhe. in:
blilIerl:ll\,
K.H.J.
Buschow.
North Holland. Amsterdam
(Ed.).
IW3.
Vol. 7. p, 3oi. <‘.I I. de (iroot. F.R. dc Boer. K.I I.J. Buachow. %. Hu. W.B. Y&n. Alloy5 Camp. 33
J.
( I‘~OO) lxx.
(‘.I I. de (iroca. l”.R. dc Bosr ilntl K.I 1.J. IJt~\chow. l’hjsicii
13(111
prcvd. (i..l.
I.ou~!.
(i.K.
Milri\\l1\~1\~, S Ml\hril. O.A. I’rmglc. %,
YCl\Ul, 11.1’. Mltltlll~lO~l, I’lrys.
(i.tl.0.
K
I I .I
I3ll~~‘llOM, I’. (~lUltl)Cilll.
I Irl, W.H. .I
AlIpl.
70 ( I?)%1) 5.38 1, I)ili~ltkr~~~~.I?J. Kelly. M.Ia.1I. S~hm~rlmltl\. l’hy\. Rev. I! 5.i
( I ‘Ml ) I ‘bl I 5 171tl. tli~rbar;~ C‘. Btick. R. Lallairc. I). I-‘iIcc;lrtl. J. Phy\. 32 ( I07 1) 200. IHI I’. k$mli. C.D. Graham. J. Appl. Phys. 42 ( IO7 I ) I209. 1’4 J.J. van don Broek. H. %ijl\tra. IEEE Trans. Map. MiIg. 231.
S~l~pl Cl
7
( IO71 )