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Ferromagnetic, dense Kondo behaviour in the alloys, CeNixGa4−x and CeCuxGa4−x
~ )
Solid State Communications, Mol. 81, No. 11, pp. 901-904, 1992. Printed in Great Britain.
0038-I09819255.00+.00 Pergamon Press plc
FERROMAGNETIC, DENSE KONDO BEHAVIOUR IN THE ALLOYS ,
CeNixGa4. x AND CeCuxGa4. x E.V. Sampathkumaran and L Das Tara Institute of Fundamental Research, Homi Bkobha Road, Bombay..400005, India (Received by C.N.R. Rao, Dec 23, 1991)
The results of electrical resistivity (1.4-300K) ~ t s alloys, CeNixGa4_ x (x = 0.5, 0.625, 0.75, 0.875 and
on the 1.1) and
CeCuxGa4. x ( x = 0.5, 1.0, 1.25 and 1.5) are reported. The results show the existence of magnetic ordering below 6K for Ga rich alloys (among the compositions investigated), whereas increasing the Ni and Cu content depresses magnetic ordering. Considering that the isothermal magnetizaton below 4.5K as a function of applied magnetic field tends to saturate, Ga rich compositions are fenvmagnetic, p data exhibit distinct anomalies characterizing Kondo effect and hence these alloys are ferromagnetic Kondo lattices.
Inspire of concentrated efforts for the past several years to understand a variety of interesting phenomena exhibited by Ce systemsI, much remains to be done to understand the detailed mechanism of ordering phenomena. It has been generally believed that the magnetically ordered Kondo lattices of Ce compounds exhibit antiferromagnetism due to the inherent antiferromagnetic coupling at the Ce site. While this is generally true, a few
of stoichiometry. distinct anomalies Kondo lauiccs.
The samples, CeNixGa4. x (x ffi 0.5, 0.625, 0.75, 0.875 and 1.1) and C e ~ x G a 4 . x (x = 0.5, 1.0, 1.25 and 1.5), were Inepared by arc melting stoichiome~ amounts of constituent elements. The ingots were annealed a t 600°C for 350hrs in an evac,_,~t_ed sealed quartz mhe. We have not prepared other compositions at the nickel/copper rich side as well as at the Ga rich side, as it is known8 that such attempts result in mulfiphase specimens. X-ray diffraction
compounds - Ce~i2.xGax 2, CeRu2Ge2 3, CePtl.xNix 4, CeSi2.xGex 5 and possibly C.ePdSb6 - are known to exhibit ferromagnetic ground state. Serious theoretical efforts have been initiated 7 to
patterns (CU-Kc~ confirm single these specimens except for
understand a correlation between various types of magnetic ground states and the 4f conduction band coupling strength. In this article, we present the results of eleclrical-resistivity (O) measuren~nts
on
a
new
series
of alloys5,
CeNixGa4_ x and CCCuxGa4_x, crystallizing in the BaAI4 type tetragonal structure, and the results show that there is an interplay of ferromagnetism and Kondo effect as a function
Some compositions show chaxacterizing fczzomagnctic,
90[
phase the
nature case
of of
CeCUl.5Ga2.5, where additional weak unidentified lines (<10%) were observed. Electrical resistivity (p) data were taken in the temperature interval 1.4-300K employing a conventional four probe method. The lattice constants, a, c and unit-cell volume V, for Ni and Cu specimens are shown in Fig.1. As reported earlier 8, the concenuation
FERROMAGNETIC, DENSE KONDO BEHAVIOUR
902 i
r
i
__
I
!
Vol. 81, No. 11 '
CeCu x Go4. x
(o) .....
'
60
. ....
c.= N~.= C,o=.~............. m "
190
50
....'"iCe mo.==..~. ~in 40
186
/."
I048
v u
10.40
"o
"¢)E 84
./-
11
/.//
142 1761
1-01
4.29 o
me
LIJ Q: 4.25
d
'
d
'
,
unit-cell
~,..
56O
:
volume
V
(:t:
...ol......... ' ....... "
"~....
4(I0
c
/CeN40"lT"J G63.r~ ~ " ""
CINIIjGO = •
I IO0
0
for
I 200
TEMPERATURE
CeNixGa4_ x and CeCUxGa4. x specimens. The line~ through the dam points serve as guides to the eyes.
"
. ..., • ........
-\
520
Figure 1 constants, a (:1: 0.004A), and
6001
,
X
0.004A)
. .....
/
>-
10.26
lauice
...-"
//./'
il // ...... ...-"
I--
The
....
.........
i
10.30
~
..... .
i
300
(K)
i
i (b)
40
Ce Nio. s G o , . 5
dependence of the unit ccL1 dimensions is non-linear exhibiting a positive deviation for the c ~ and a nmlr~v¢ dcvigtion for the a parameter. In the case of nickel series, a maximum is seen for c for the i n ~ ¢,once~ (x = 0.62.5 and 0.75). It, appears 8 that these dcviadons in th© lance parameters ms=It from the pre~crrcd occupation of "the 4c-site by the Cu/Ni atoms for smallcr values of x, l_e-~ing to the formation of Cu-Cu/Ni-Ni dumb-bell. Further increase of Cu/Ni leads to the occupation of the alternative dd site, thereby reducing both the c parameter and thc unit-cell volume when reaching stadsdcal disuibufion. The results of electrical resistivity (p) nmasuren~nts for Ni and Cu specimens are shown in Figs.2 and 3 respectively. In order to higldight the features due to magnetic ordering, the low mrnpenmm~ dam are plotted in an expanded form in Figs.2b and 31). The resistivity decreases with temperature and there is a broad
~0 2O
Ce Nio.usGas.srs : / .0 0
20
>" I--
I0 20
i,i I1"
I0
/
/
Ce Nio.TsGo3.rs
:
>
I-,Oq
..-
...~;
j:/
..
~ "xx N "~
30'
. ...
•
"x
"...
%. ,, %
',.
Ce Nio.arsGo3jzs
20
C e N i f iGo= i " ' " '
tO
= 0
~'~
"i"=
I
JO TEMPERATURE
20 (K)
Figure 2 (a) ElectricaJ rzsisfivity of CeNixGa4. x alloys in the temperature range 1.4-300K Co) The resistivity behaviour at low temperatures for these alloys is shown in an expanded form.
Vol. 81, No. 11
FERROMAGNETIC, DENSE KONDO BEHAVIOUR i
{o)
220
arises from the interplay between crystal-field and Kondo effects, as in other Cc systems 1. It is impommt to note that this feature disappears for higher values of x. Thus, this series of compounds arc unique in the sense that
.
CeCuo.sG%s
. ....."
L 180
........... C,tuG% / ..y"
....
...
......
..-
.y'
......'"
903
the
...."
features
due
to
crysud-field
effects
am
stoichiomcury.
The
low
~ ,4o
'very
ne
temperature resistivity dam (Figs.2b and 3b) also show the sensitivity of the ground state to the stoichiorrmu'y. There is a distinct minimum in the p dam for the Ni-rich and Cu-rich specimens, showing thereby the dominance of
,." "'
128
.. " ' " " ......
,2o~
............ ~c* Cu,sGo,s
0
100
sensitive
Kondo
20O
lower i
i
.'
/ o >I-
20
C¢CuGo5 ....."'" .......' .....-..
........-.' • "~
.'"
.../"
:;" ~,~ .: ." "....
..."
• .""
compositions.
Grin et al8
The
show
6K),
a
followed
reported that the such
compositions
data
peak at by
a
isothermal at
41(
at higher fields with saturation moment of the order of l g B. magnetization ~ n t s performed on specimens confirm this behaviour. Taking
the The our
this
satura~on into account, we can state that these samples undergo ferromagnetic ordering. However, the anomalies due to magnetic ordering disappear (Figs.2b and 3b) for higher concentrations of Cu
•..... \'-.... CeCu,~GoZ.75....' '"...
such
concentrations
magnefiz~on for undergo saturation
....'"
•'
Cu/Ni
tmnlXn'atures (at about
drop.
{b) . ....... -
C,Cu~C,~s
,~"'
effect for
for initial
TEMPERATURE (K)
to
..'"
W
"~CeCUl. s GO2. 5
and Ni in the temperautre range of investigation and there is a tendency for p to saturate below I tO
I
2K
20
TEMPERATURE
(K)
FIGURE 3 (a) Electrical resistivity of CeCuxGa4. x alloys in the tcrnperatum range 1.4-300K Co) The resistivity behaviour at low temperatures for these alloys is shown in an expanded form.
typical of Kondo
It between
curvature
for initial Cu
and
(0.5, 0.625
Ni
in and
the (x =
temperature
interval
0.5, 1.0 and
0.75) substitutions.
1.25) We
have not attempted to make corresponding La specimens to derive the knowledge about the phonon contribution, as we believe that reliable values due to obtained for
contribution may not be such a disordered lattice, particularly in polycrystalline spe~ruens. It may, however, be stated that this broad feature phonon
and
Ni
appears that there is a the dependence of Tc on
concentration By
50-200K
if Cu
content.
occupation upward
effect. Even
rich specimens tend to order at further lower temperatures (
this we
and of
the
Cu/Ni mean
correlation the Cu/Ni preferential site
mentioned
in
that the occupation
this article. of
Cu/Ni
at the 4e site tends to favour ferromagnetism, whereas 4d sire occupation results in non-magnetism. To summarize, we present evidence for the presence of a competition between fe~ronmguetism and Kondo effect in two Ce-based alloy series. The ground state appears to be very sendtive to atoms
stoichioumlzy. CeNi0.75Ga3.25 con~__d,~cd to
We
propose
that
dm alloys
like
and C¢(~1.25Ga2.75 can be be f c r ~ c danse Kondo
904
FERROMAGNETIC, DENSE KONDO BEHAVIOUR
systems. We thank Prof. R. support and encouragement.
4. Vijayaraghavan
for
his 5.
References
1.
2. 3.
See 'Wheoretical and experimental aspects of valence fluctuations and heavy fermions", edited by L.C. Gupta and S.K. Malik (New York and London, Plenum, 1987) and references therein. H. Mori, N. Sato and T. Satoh, Solid Sta~ Commun., 49..., 955 (1984). I. Felner and I. Nowik, J. Phys. Chem. Solids, 46, 681 (1985); M.J. Besnus, A. Essaihi, N. I-law_~J~_~ui, ~ G. Fischer, J.P. Kappler, A. Meyer, J. Peirre, P. I-laen and P. Lejay, Physica B 17___11,357 (1991).
6. 7.
8.
Vol. 81, No. 11
D. Gignoux and I.G. gomez Sal, Phys. Rev. B 30, 3969 (1984). H. Mori, H. Y ~ and N. Sam, J. Low Temp. Phys. 58__, 513 (1985); H. Yashirna, C.F. Lin, T. Satoh, H. Hiroyoshi and K. Kohn, Solid State Commun., 57__, 793 0986); H. Yashima, H. Mori, T. Sarah and K. Koln, Solid State Commun., 43, 193 (1982). S.K. Malik and D.T. Adroja, Phys. Rev. B 43, 6295 (1991). W. Nolling, V. Eyert and A. Ramakanth, in Ref. 1, p.597; P. Fazckas' and E. MUller-Harunann, Z. Phys. B - Cond. Matter 85, 285 (1991); R. Freytag and J. Keller, ibid, 8.__55,87 (1991). Yu. N. Grin, P. Rogl and H. Noel, J. Less Common Metals, 162, 361 (1990); Yu. N. Grin, K. I-liebl, P. Rogl and H. Noel, J. Less Common Metals, 16___22,371 (1990).
Solid State Communications, Mol. 81, No. 11, pp. 901-904, 1992. Printed in Great Britain.
0038-I09819255.00+.00 Pergamon Press plc
FERROMAGNETIC, DENSE KONDO BEHAVIOUR IN THE ALLOYS ,
CeNixGa4. x AND CeCuxGa4. x E.V. Sampathkumaran and L Das Tara Institute of Fundamental Research, Homi Bkobha Road, Bombay..400005, India (Received by C.N.R. Rao, Dec 23, 1991)
The results of electrical resistivity (1.4-300K) ~ t s alloys, CeNixGa4_ x (x = 0.5, 0.625, 0.75, 0.875 and
on the 1.1) and
CeCuxGa4. x ( x = 0.5, 1.0, 1.25 and 1.5) are reported. The results show the existence of magnetic ordering below 6K for Ga rich alloys (among the compositions investigated), whereas increasing the Ni and Cu content depresses magnetic ordering. Considering that the isothermal magnetizaton below 4.5K as a function of applied magnetic field tends to saturate, Ga rich compositions are fenvmagnetic, p data exhibit distinct anomalies characterizing Kondo effect and hence these alloys are ferromagnetic Kondo lattices.
Inspire of concentrated efforts for the past several years to understand a variety of interesting phenomena exhibited by Ce systemsI, much remains to be done to understand the detailed mechanism of ordering phenomena. It has been generally believed that the magnetically ordered Kondo lattices of Ce compounds exhibit antiferromagnetism due to the inherent antiferromagnetic coupling at the Ce site. While this is generally true, a few
of stoichiometry. distinct anomalies Kondo lauiccs.
The samples, CeNixGa4. x (x ffi 0.5, 0.625, 0.75, 0.875 and 1.1) and C e ~ x G a 4 . x (x = 0.5, 1.0, 1.25 and 1.5), were Inepared by arc melting stoichiome~ amounts of constituent elements. The ingots were annealed a t 600°C for 350hrs in an evac,_,~t_ed sealed quartz mhe. We have not prepared other compositions at the nickel/copper rich side as well as at the Ga rich side, as it is known8 that such attempts result in mulfiphase specimens. X-ray diffraction
compounds - Ce~i2.xGax 2, CeRu2Ge2 3, CePtl.xNix 4, CeSi2.xGex 5 and possibly C.ePdSb6 - are known to exhibit ferromagnetic ground state. Serious theoretical efforts have been initiated 7 to
patterns (CU-Kc~ confirm single these specimens except for
understand a correlation between various types of magnetic ground states and the 4f conduction band coupling strength. In this article, we present the results of eleclrical-resistivity (O) measuren~nts
on
a
new
series
of alloys5,
CeNixGa4_ x and CCCuxGa4_x, crystallizing in the BaAI4 type tetragonal structure, and the results show that there is an interplay of ferromagnetism and Kondo effect as a function
Some compositions show chaxacterizing fczzomagnctic,
90[
phase the
nature case
of of
CeCUl.5Ga2.5, where additional weak unidentified lines (<10%) were observed. Electrical resistivity (p) data were taken in the temperature interval 1.4-300K employing a conventional four probe method. The lattice constants, a, c and unit-cell volume V, for Ni and Cu specimens are shown in Fig.1. As reported earlier 8, the concenuation
FERROMAGNETIC, DENSE KONDO BEHAVIOUR
902 i
r
i
__
I
!
Vol. 81, No. 11 '
CeCu x Go4. x
(o) .....
'
60
. ....
c.= N~.= C,o=.~............. m "
190
50
....'"iCe mo.==..~. ~in 40
186
/."
I048
v u
10.40
"o
"¢)E 84
./-
11
/.//
142 1761
1-01
4.29 o
me
LIJ Q: 4.25
d
'
d
'
,
unit-cell
~,..
56O
:
volume
V
(:t:
...ol......... ' ....... "
"~....
4(I0
c
/CeN40"lT"J G63.r~ ~ " ""
CINIIjGO = •
I IO0
0
for
I 200
TEMPERATURE
CeNixGa4_ x and CeCUxGa4. x specimens. The line~ through the dam points serve as guides to the eyes.
"
. ..., • ........
-\
520
Figure 1 constants, a (:1: 0.004A), and
6001
,
X
0.004A)
. .....
/
>-
10.26
lauice
...-"
//./'
il // ...... ...-"
I--
The
....
.........
i
10.30
~
..... .
i
300
(K)
i
i (b)
40
Ce Nio. s G o , . 5
dependence of the unit ccL1 dimensions is non-linear exhibiting a positive deviation for the c ~ and a nmlr~v¢ dcvigtion for the a parameter. In the case of nickel series, a maximum is seen for c for the i n ~ ¢,once~ (x = 0.62.5 and 0.75). It, appears 8 that these dcviadons in th© lance parameters ms=It from the pre~crrcd occupation of "the 4c-site by the Cu/Ni atoms for smallcr values of x, l_e-~ing to the formation of Cu-Cu/Ni-Ni dumb-bell. Further increase of Cu/Ni leads to the occupation of the alternative dd site, thereby reducing both the c parameter and thc unit-cell volume when reaching stadsdcal disuibufion. The results of electrical resistivity (p) nmasuren~nts for Ni and Cu specimens are shown in Figs.2 and 3 respectively. In order to higldight the features due to magnetic ordering, the low mrnpenmm~ dam are plotted in an expanded form in Figs.2b and 31). The resistivity decreases with temperature and there is a broad
~0 2O
Ce Nio.usGas.srs : / .0 0
20
>" I--
I0 20
i,i I1"
I0
/
/
Ce Nio.TsGo3.rs
:
>
I-,Oq
..-
...~;
j:/
..
~ "xx N "~
30'
. ...
•
"x
"...
%. ,, %
',.
Ce Nio.arsGo3jzs
20
C e N i f iGo= i " ' " '
tO
= 0
~'~
"i"=
I
JO TEMPERATURE
20 (K)
Figure 2 (a) ElectricaJ rzsisfivity of CeNixGa4. x alloys in the temperature range 1.4-300K Co) The resistivity behaviour at low temperatures for these alloys is shown in an expanded form.
Vol. 81, No. 11
FERROMAGNETIC, DENSE KONDO BEHAVIOUR i
{o)
220
arises from the interplay between crystal-field and Kondo effects, as in other Cc systems 1. It is impommt to note that this feature disappears for higher values of x. Thus, this series of compounds arc unique in the sense that
.
CeCuo.sG%s
. ....."
L 180
........... C,tuG% / ..y"
....
...
......
..-
.y'
......'"
903
the
...."
features
due
to
crysud-field
effects
am
stoichiomcury.
The
low
~ ,4o
'very
ne
temperature resistivity dam (Figs.2b and 3b) also show the sensitivity of the ground state to the stoichiorrmu'y. There is a distinct minimum in the p dam for the Ni-rich and Cu-rich specimens, showing thereby the dominance of
,." "'
128
.. " ' " " ......
,2o~
............ ~c* Cu,sGo,s
0
100
sensitive
Kondo
20O
lower i
i
.'
/ o >I-
20
C¢CuGo5 ....."'" .......' .....-..
........-.' • "~
.'"
.../"
:;" ~,~ .: ." "....
..."
• .""
compositions.
Grin et al8
The
show
6K),
a
followed
reported that the such
compositions
data
peak at by
a
isothermal at
41(
at higher fields with saturation moment of the order of l g B. magnetization ~ n t s performed on specimens confirm this behaviour. Taking
the The our
this
satura~on into account, we can state that these samples undergo ferromagnetic ordering. However, the anomalies due to magnetic ordering disappear (Figs.2b and 3b) for higher concentrations of Cu
•..... \'-.... CeCu,~GoZ.75....' '"...
such
concentrations
magnefiz~on for undergo saturation
....'"
•'
Cu/Ni
tmnlXn'atures (at about
drop.
{b) . ....... -
C,Cu~C,~s
,~"'
effect for
for initial
TEMPERATURE (K)
to
..'"
W
"~CeCUl. s GO2. 5
and Ni in the temperautre range of investigation and there is a tendency for p to saturate below I tO
I
2K
20
TEMPERATURE
(K)
FIGURE 3 (a) Electrical resistivity of CeCuxGa4. x alloys in the tcrnperatum range 1.4-300K Co) The resistivity behaviour at low temperatures for these alloys is shown in an expanded form.
typical of Kondo
It between
curvature
for initial Cu
and
(0.5, 0.625
Ni
in and
the (x =
temperature
interval
0.5, 1.0 and
0.75) substitutions.
1.25) We
have not attempted to make corresponding La specimens to derive the knowledge about the phonon contribution, as we believe that reliable values due to obtained for
contribution may not be such a disordered lattice, particularly in polycrystalline spe~ruens. It may, however, be stated that this broad feature phonon
and
Ni
appears that there is a the dependence of Tc on
concentration By
50-200K
if Cu
content.
occupation upward
effect. Even
rich specimens tend to order at further lower temperatures (
this we
and of
the
Cu/Ni mean
correlation the Cu/Ni preferential site
mentioned
in
that the occupation
this article. of
Cu/Ni
at the 4e site tends to favour ferromagnetism, whereas 4d sire occupation results in non-magnetism. To summarize, we present evidence for the presence of a competition between fe~ronmguetism and Kondo effect in two Ce-based alloy series. The ground state appears to be very sendtive to atoms
stoichioumlzy. CeNi0.75Ga3.25 con~__d,~cd to
We
propose
that
dm alloys
like
and C¢(~1.25Ga2.75 can be be f c r ~ c danse Kondo
904
FERROMAGNETIC, DENSE KONDO BEHAVIOUR
systems. We thank Prof. R. support and encouragement.
4. Vijayaraghavan
for
his 5.
References
1.
2. 3.
See 'Wheoretical and experimental aspects of valence fluctuations and heavy fermions", edited by L.C. Gupta and S.K. Malik (New York and London, Plenum, 1987) and references therein. H. Mori, N. Sato and T. Satoh, Solid Sta~ Commun., 49..., 955 (1984). I. Felner and I. Nowik, J. Phys. Chem. Solids, 46, 681 (1985); M.J. Besnus, A. Essaihi, N. I-law_~J~_~ui, ~ G. Fischer, J.P. Kappler, A. Meyer, J. Peirre, P. I-laen and P. Lejay, Physica B 17___11,357 (1991).
6. 7.
8.
Vol. 81, No. 11
D. Gignoux and I.G. gomez Sal, Phys. Rev. B 30, 3969 (1984). H. Mori, H. Y ~ and N. Sam, J. Low Temp. Phys. 58__, 513 (1985); H. Yashirna, C.F. Lin, T. Satoh, H. Hiroyoshi and K. Kohn, Solid State Commun., 57__, 793 0986); H. Yashima, H. Mori, T. Sarah and K. Koln, Solid State Commun., 43, 193 (1982). S.K. Malik and D.T. Adroja, Phys. Rev. B 43, 6295 (1991). W. Nolling, V. Eyert and A. Ramakanth, in Ref. 1, p.597; P. Fazckas' and E. MUller-Harunann, Z. Phys. B - Cond. Matter 85, 285 (1991); R. Freytag and J. Keller, ibid, 8.__55,87 (1991). Yu. N. Grin, P. Rogl and H. Noel, J. Less Common Metals, 162, 361 (1990); Yu. N. Grin, K. I-liebl, P. Rogl and H. Noel, J. Less Common Metals, 16___22,371 (1990).