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Kondo effect of trivalent Tm in Y0.9Tm0.1S
Journal of Magnetism and Magnetic Materials 31-34 (1983) 435-436 KONDO
EFFECT
OF TRIVALENT
P. H A E N , F. L A P I E R R E ,
435
T i n I N Yo.gTmo.tS
J.M. MIGNOT
a n d J. F L O U Q U E T
Centre de Recherches sur les Trbs Basses Temperatures, CNRS, BP 166 X, 38042 Grenoble-Cedex, France
F. H O L T Z B E R G
a n d T. P E N N E Y
IBM T.J. Watson Research Center, Yorktown Heights, N Y 10598, USA
The existence of a Kondo effect in a trivalent alloy Yo.gTm0aS is shown by the Curie-Weiss behavior of the susceptibility and by a In T decrease of AO = Pa,oy - Ors above - 12 K comparable with that observed in TmS. Comparisons are made with the Kondo dilute alloys of the intermediate valent system (Y,Tm)Se.
Some fundamental questions still remain open in the interpretation of the properties of 4f instability compounds. In particular, it is important to know if the anomalous character of the rare earths is preserved when diluted in a nonmagnetic host. For the case of thulium, an answer to this question has been already given through the study of the system (Y,Tm)Se. It has been shown that the Tm ions are in an intermediate valence (IV) state as in TmSe and that in the dilute limit, x ~< 0.2, Y~ _xTmxSe alloys exhibit a K o n d o effect [1]. It is also interesting to observe the behavior of trivalent T m atoms in the dilute state. In this paper, we report susceptibility and resistivity measurements performed on single crystals of the alloy Y i - x T m x S with nominal composition x = 0.1. They show a K o n d o effect which will be compared with that of (Y,Tm)Se alloys and with the concentrated K o n d o behavior of the trivalent compound TmS [2]. The trivalent character of the T m ions in Y~ _xTmxS has been observed recently by photoemission spectroscopy [3], and is consistent with the lattice parameter a 0 = 5.485 A determined from pieces cut from our samples; this value is almost equal to the one interpolated between the values of a 0 for YS and TInS (respectively 5.495 and 5.417 ,/~). The susceptibility measurements were performed between 1.2 and 4.2 K by a conventional extraction technique and above 4.2 K with a S Q U I D magnetometer in a field of 1 kOe, where the magnetization is linear with H. The upper curve in fig. 1 represents the plot of the inverse susceptibility X - I ( T ) between 4.2 and 160 K. It shows a Curie-Weiss behavior above - 60 K with 0p ~ - 2 0 K. The effective moment determined from this variation, # e l f = 7 . 1 # n / T m , is almost equal to that deduced from the Curie-Weiss susceptibility of TmS in the same temperature range [4], but is lower than the free-ion value of 7.57 # a / T m . A negative curvature of X - I ( T ) occurs below - 6 0 K. However, the plot of X - l ( T ) between 1.2 and 40 K (lower curve in fig. 1) can be fitted with another Curie-Weiss law with 0LT = --7 K. This behavior suggests the existence of a K o n d o 0304-8853/83/0000-0000/$03.00
-20
0
20
40
60
80
'
'
100
120
'
140 7(K)
'
'
'
30
Yo.9Tmo.1S
/
20
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~
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0 8 6 4
lr /
2 ./.
-10
i
0
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,
10
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! 20
a
! 30
,
T(K)
0 /~0
Fig. i. Variation of the inverse susceptibility of Yo.gTmo.~Swith T between 4.2 and 160 K (upper curve) and between 1.2 and 40 K (lower curve). effect in Y0.gTm0.~S with a characteristic temperature T K of the order of 7 K. The behavior of the resistivity P~loy of Yo.gTm0.1S and of the difference AO = P a l l o y - PYS, where Ors is the resistivity of the host compound YS, confirms the existence of a K o n d o effect. Fig. 2 represents the variations of Pa,oy, Ors and Ap between 1.8 K and room temperature (RT) as a function of logT. On cooling, a deep minimum occurs in Pa,oy at - 60 K followed by a l n T i n c r e a s e for 37 _< T_< 12 K. Below 12 K, Pa,oy varies less rapidly with T and a plateau is expected at very low temperature. PYs, as measured on a single crystal, exhibits a normal metallic variation and reaches a residual value P 0 - 6 # ~ cm below - 1 5 K. (Notice that this curve is displaced upwards by 5#~ cm compared with the others in fig. 2). Pvs drops to zero at T~ = 2.85 K, confirming a previous report [5] on superconductivity in YS. At low temperatures, since Pvs is constant, the variation of Ap is identical to that of P~,oy. Above - 12 K, AO shows a l n T behavior which extends almost up to room temperature, whereas in P~,oy this behavior
© 1983 N o r t h - H o l l a n d
436 4C
P. Haen et aL / Kondo effect of Trn in Yo.gTrno i S
( p~.cm )
!
i
I
I
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i 20
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Fig. 2. Plots of the resistivity of single crystals of Y0.gTm0.1S and YS and of their difference Ap versus log T. The dashed lines represent the extreme variations of Ap caused by an uncertainty of + 10% in the resistivity of each compound.
reported for Kondo alloys with cerium impurities [6]. It is interesting to compare the Kondo behavior of trivalent T m in Y0.gTm0.~S with that of IV T m in dilute (Y,Tm)Se alloys. The value of ~ differs only by a factor of - 2 (for Yl_~TmxSe, ~ varies from 0.25 to 0.17 Fit c m / % T m with x increasing from 0.01 to 0.2 [1]), but the estimated values of T K differ by about two orders of magnitude (TK~<0.3-0.1 K in Yl_xTmxSe). Another major difference is that interactions between T m atoms occur at very low temperatures in Y~_xTmxSe, even with x as low as 0.01 [7], but there is no indication for such a phenomenon above 0.05 K in Y0.gTm0.1S, according to preliminary experiments. It must be pointed out that the l n T slope in TmS (67 to 4 4 / t i t cm [2,8]) is comparable with that extrapolated from the value of ~ in Y0.gTm0.tS (i.e. 42 /~it cm for 100% T m atoms). In contrast, there is a very large difference between the values of ~ in (Y,Tm)Se alloys and in stoichiometric TmSe: ~ is 18 times higher in the latter compound than in the former alloys. This result clearly indicates that cooperative effects are essential in TmSe. In conclusion, this study provides the first experimental evidence for a Kondo effect of dilute trivalent thulium impurities in a non-magnetic host. Comparison with pure TmS supports the view that the latter comp o u n d is indeed a concentrated Kondo compound. The system (Y,Tm)S therefore appears to be a promising candidate for the study of the ground state properties of Kondo ions with large orbital degeneracy.
References appears only in a short range of temperature. However, Ap is subject to an experimental error due to the uncertainty in the absolute values of #ahoy and Pvs. This uncertainty, which results essentially from the error in the sample dimensions, can be estimated to + 10%. This implies that the values of 3p can differ from those represented on fig. 2 by as much as - + 6 ~tit cm at R T and - + 4 / ~ D cm below - 100 K. The dashed lines in fig. 2 represent the variation of Ap defined by these two limits. Fortunately, it appears that the slope of these two curves is almost equal to that of the previous one for 12 < T_< 100 K. Thus, the value of this slope, ~ = ( 1 / x ) l d p / d l n T I - - 0 . 4 2 /tit c m / % T m , can be considered as representative of the Kondo behavior of Y0.gTm0.1S. This value of ~ is of the same order as those
[1] P. Haen, O. Laborde, F. Lapierre, J.M. Mignot, F.Holtzberg and T. Penney, in" Proc. Int. Conf. on Valence Instabilities, eds. P. Wachter and H. Boppart (North-Holland, Amsterdam, 1982) p. 423. [2] F. Lapierre, P. Haen, B. Coqblin, M. Ribault and F. Holtzberg, Physica 108B (1981) 1351. [3] N. Mttrtensson, B. Reihl, R.A. Pollak, F. Holtzberg, G. Kaindl and D.E. Eastman, Phys. Rev. B26 (1982) 648. [4] E. Bucher, K. Andres, F.J. Di Salvo, J.P. Maita, A.C. Gossard, A.S. Cooper and G.W. Hull, Jr., Phys. Rev. BI 1 (1975) 500. [5] F. Hulliger and G.W, Hull, Jr., Solid State Commun. 8 (1970) 1379. [6] W. Felsch and K. Winzer, Solid State Commun. 13 (1973) 569; K. Samwer and K. Winzer, Z. Phys. B25 (1976) 269. [7] J.L. Genicon, P. Haen, F. Holtzberg, F. Lapierre and J.M. Mignot, Physica 108B (1981) 1355. [8] P. Haen and F. Lapierre, unpublished.
EFFECT
OF TRIVALENT
P. H A E N , F. L A P I E R R E ,
435
T i n I N Yo.gTmo.tS
J.M. MIGNOT
a n d J. F L O U Q U E T
Centre de Recherches sur les Trbs Basses Temperatures, CNRS, BP 166 X, 38042 Grenoble-Cedex, France
F. H O L T Z B E R G
a n d T. P E N N E Y
IBM T.J. Watson Research Center, Yorktown Heights, N Y 10598, USA
The existence of a Kondo effect in a trivalent alloy Yo.gTm0aS is shown by the Curie-Weiss behavior of the susceptibility and by a In T decrease of AO = Pa,oy - Ors above - 12 K comparable with that observed in TmS. Comparisons are made with the Kondo dilute alloys of the intermediate valent system (Y,Tm)Se.
Some fundamental questions still remain open in the interpretation of the properties of 4f instability compounds. In particular, it is important to know if the anomalous character of the rare earths is preserved when diluted in a nonmagnetic host. For the case of thulium, an answer to this question has been already given through the study of the system (Y,Tm)Se. It has been shown that the Tm ions are in an intermediate valence (IV) state as in TmSe and that in the dilute limit, x ~< 0.2, Y~ _xTmxSe alloys exhibit a K o n d o effect [1]. It is also interesting to observe the behavior of trivalent T m atoms in the dilute state. In this paper, we report susceptibility and resistivity measurements performed on single crystals of the alloy Y i - x T m x S with nominal composition x = 0.1. They show a K o n d o effect which will be compared with that of (Y,Tm)Se alloys and with the concentrated K o n d o behavior of the trivalent compound TmS [2]. The trivalent character of the T m ions in Y~ _xTmxS has been observed recently by photoemission spectroscopy [3], and is consistent with the lattice parameter a 0 = 5.485 A determined from pieces cut from our samples; this value is almost equal to the one interpolated between the values of a 0 for YS and TInS (respectively 5.495 and 5.417 ,/~). The susceptibility measurements were performed between 1.2 and 4.2 K by a conventional extraction technique and above 4.2 K with a S Q U I D magnetometer in a field of 1 kOe, where the magnetization is linear with H. The upper curve in fig. 1 represents the plot of the inverse susceptibility X - I ( T ) between 4.2 and 160 K. It shows a Curie-Weiss behavior above - 60 K with 0p ~ - 2 0 K. The effective moment determined from this variation, # e l f = 7 . 1 # n / T m , is almost equal to that deduced from the Curie-Weiss susceptibility of TmS in the same temperature range [4], but is lower than the free-ion value of 7.57 # a / T m . A negative curvature of X - I ( T ) occurs below - 6 0 K. However, the plot of X - l ( T ) between 1.2 and 40 K (lower curve in fig. 1) can be fitted with another Curie-Weiss law with 0LT = --7 K. This behavior suggests the existence of a K o n d o 0304-8853/83/0000-0000/$03.00
-20
0
20
40
60
80
'
'
100
120
'
140 7(K)
'
'
'
30
Yo.9Tmo.1S
/
20
,f
J
~
~
(era_u,
...7
Im-'~
0 8 6 4
lr /
2 ./.
-10
i
0
.
,
10
,
! 20
a
! 30
,
T(K)
0 /~0
Fig. i. Variation of the inverse susceptibility of Yo.gTmo.~Swith T between 4.2 and 160 K (upper curve) and between 1.2 and 40 K (lower curve). effect in Y0.gTm0.~S with a characteristic temperature T K of the order of 7 K. The behavior of the resistivity P~loy of Yo.gTm0.1S and of the difference AO = P a l l o y - PYS, where Ors is the resistivity of the host compound YS, confirms the existence of a K o n d o effect. Fig. 2 represents the variations of Pa,oy, Ors and Ap between 1.8 K and room temperature (RT) as a function of logT. On cooling, a deep minimum occurs in Pa,oy at - 60 K followed by a l n T i n c r e a s e for 37 _< T_< 12 K. Below 12 K, Pa,oy varies less rapidly with T and a plateau is expected at very low temperature. PYs, as measured on a single crystal, exhibits a normal metallic variation and reaches a residual value P 0 - 6 # ~ cm below - 1 5 K. (Notice that this curve is displaced upwards by 5#~ cm compared with the others in fig. 2). Pvs drops to zero at T~ = 2.85 K, confirming a previous report [5] on superconductivity in YS. At low temperatures, since Pvs is constant, the variation of Ap is identical to that of P~,oy. Above - 12 K, AO shows a l n T behavior which extends almost up to room temperature, whereas in P~,oy this behavior
© 1983 N o r t h - H o l l a n d
436 4C
P. Haen et aL / Kondo effect of Trn in Yo.gTrno i S
( p~.cm )
!
i
I
I
\\\
3C
~p
",\\
25
~ \\
"~x\x
,20
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20
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'
15
\~\\\
'\"' \"',
15
J 10
i 2
t 5
I 10
i 20
10
\\\ i 50
I 100
I 5 200
Fig. 2. Plots of the resistivity of single crystals of Y0.gTm0.1S and YS and of their difference Ap versus log T. The dashed lines represent the extreme variations of Ap caused by an uncertainty of + 10% in the resistivity of each compound.
reported for Kondo alloys with cerium impurities [6]. It is interesting to compare the Kondo behavior of trivalent T m in Y0.gTm0.~S with that of IV T m in dilute (Y,Tm)Se alloys. The value of ~ differs only by a factor of - 2 (for Yl_~TmxSe, ~ varies from 0.25 to 0.17 Fit c m / % T m with x increasing from 0.01 to 0.2 [1]), but the estimated values of T K differ by about two orders of magnitude (TK~<0.3-0.1 K in Yl_xTmxSe). Another major difference is that interactions between T m atoms occur at very low temperatures in Y~_xTmxSe, even with x as low as 0.01 [7], but there is no indication for such a phenomenon above 0.05 K in Y0.gTm0.1S, according to preliminary experiments. It must be pointed out that the l n T slope in TmS (67 to 4 4 / t i t cm [2,8]) is comparable with that extrapolated from the value of ~ in Y0.gTm0.tS (i.e. 42 /~it cm for 100% T m atoms). In contrast, there is a very large difference between the values of ~ in (Y,Tm)Se alloys and in stoichiometric TmSe: ~ is 18 times higher in the latter compound than in the former alloys. This result clearly indicates that cooperative effects are essential in TmSe. In conclusion, this study provides the first experimental evidence for a Kondo effect of dilute trivalent thulium impurities in a non-magnetic host. Comparison with pure TmS supports the view that the latter comp o u n d is indeed a concentrated Kondo compound. The system (Y,Tm)S therefore appears to be a promising candidate for the study of the ground state properties of Kondo ions with large orbital degeneracy.
References appears only in a short range of temperature. However, Ap is subject to an experimental error due to the uncertainty in the absolute values of #ahoy and Pvs. This uncertainty, which results essentially from the error in the sample dimensions, can be estimated to + 10%. This implies that the values of 3p can differ from those represented on fig. 2 by as much as - + 6 ~tit cm at R T and - + 4 / ~ D cm below - 100 K. The dashed lines in fig. 2 represent the variation of Ap defined by these two limits. Fortunately, it appears that the slope of these two curves is almost equal to that of the previous one for 12 < T_< 100 K. Thus, the value of this slope, ~ = ( 1 / x ) l d p / d l n T I - - 0 . 4 2 /tit c m / % T m , can be considered as representative of the Kondo behavior of Y0.gTm0.1S. This value of ~ is of the same order as those
[1] P. Haen, O. Laborde, F. Lapierre, J.M. Mignot, F.Holtzberg and T. Penney, in" Proc. Int. Conf. on Valence Instabilities, eds. P. Wachter and H. Boppart (North-Holland, Amsterdam, 1982) p. 423. [2] F. Lapierre, P. Haen, B. Coqblin, M. Ribault and F. Holtzberg, Physica 108B (1981) 1351. [3] N. Mttrtensson, B. Reihl, R.A. Pollak, F. Holtzberg, G. Kaindl and D.E. Eastman, Phys. Rev. B26 (1982) 648. [4] E. Bucher, K. Andres, F.J. Di Salvo, J.P. Maita, A.C. Gossard, A.S. Cooper and G.W. Hull, Jr., Phys. Rev. BI 1 (1975) 500. [5] F. Hulliger and G.W, Hull, Jr., Solid State Commun. 8 (1970) 1379. [6] W. Felsch and K. Winzer, Solid State Commun. 13 (1973) 569; K. Samwer and K. Winzer, Z. Phys. B25 (1976) 269. [7] J.L. Genicon, P. Haen, F. Holtzberg, F. Lapierre and J.M. Mignot, Physica 108B (1981) 1355. [8] P. Haen and F. Lapierre, unpublished.