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Heavy fermion behaviour of the nonmagnetic CeCu4Al compound
Solid State Communications, Vol. 62, No. 4, pp. 271-274, 1987. Printed in Great Britam.
0038-1098/87 $3.00 + .00 Pergamon Journals Ltd.
H E A V Y F E R M I O N B E H A V I O U R O F T H E N O N M A G N E T I C CeCu4AI C O M P O U N D E. Bauer, E. Gratz and N. Plllmayr Institute of Experimental Physics, Technwal Umverslty Vienna, Austrm
(Recetved 22 October 1986 by P. Wachter) We present measurements of the temperature dependence of the electrical resistivity, the thermopower and the specific heat of the hexagonal compound CeCu4A1. At h~gh temperatures, the electrical resistivity is characterized by a nearly temperature independent behaviour, followed by a continuous increase below 100K. No maximum has been found down to 1.7 K. The thermopower shows a positive maximum at about 30 K. As in CeCu6 no negative values are observable in the range from 4.2 K up to a room temperature The specific heat data between 7 and 15K reveal a 7 value around 280mJ mol-Z K -2. Below this temperature range the specific heat cp/T shows a rapid rise and crosses the value of 1 J m o l - ~ K -2 at about 1.45 K. 1. I N T R O D U C T I O N
a substitution of one Cu-atom by an Al-atom. The whole family of the RECu4AI intermetalhcs (RE = rare earth) was found to crystallize in the hexagonal CaCu5 structure (P6/mmm) [12]. The substitution of Cu by A1 increases the average electron density per atom and therefore a significant change of the Kondo lattice behaviour of CeCu5 has to be expected. In order to investigate the variation of the physical properties depending on such a substitution we studied CeCu4A1. Polycrystalhne samples of CeCu4A1 and LaCu4AI were prepared by high frequency melting under argon atmosphere and subsequently annealed for 7 days at 600°C. The phase purity of the samples was checked by Debye-Scherrer photographs and by X-ray &ffractlon, usmg a conventional Siemens X-ray diffractometer. No traces of foreign phases were detected by these procedures. Electrical resistivity data were taken by means of a conventional four probe technique. The thermopower values were measured by a differential method, where Pb serves as reference material The specific heat was measured in a fully automated Nernst calorimeter. Previous measurements of the lattice constants (a = 5.195A, c = 4.188A) [12] as well as of the magnetic susceptibility [13] indicate a 3 + state for the Cerium ion in CeCunAI, within the uncertainty of such methods. The paramagnetic Curie temperature was found to lie at - 14 K.
IN R E C E N T YEARS growing interest has been focused on nearly trivalent Ce-based intermetallic compounds, whose unusual electronic properties are commonly referred to the existence of Kondo-type interaction. Among these properties, peculiar magnetic ordering with reduced moments as in CeAI2 [1], Fermiliquid behaviour as m CeA13 [2] or heavy fermlon superconductivity as in CeCu2Si2 [3] are of great experimental and theoretical relevance (for a revtew see e.g. [4, 5]). Within these Ce compounds the nonmagnetic CeA13 and C e f u 6 demonstrate the highest known 7 values of the specific heat ( ~ 1500mJ mol -~ K-2). This fact and most of the other physical properties have been attributed to the formation of a giant resonance at the Fermi-edge due to the anomalous proximity of the Ce 4 f level [5]. This resonance (Abrikosov-Suhl resonance, ASR) starts to increase strongly below a characteristic temperature, usually called the Kondo-temperature TK. The rise of the ASR ~s intimately connected to the increase of the 7 value at low temperatures. However, a modification of the ASR below a certain temperature T* (coherence temperature) is responsible for a drop of cp/T, giving rise to a maximum at T* [6]. Indeed, this behaviour was found for CeCu6 [7], for CeA13 [8], for CeCuz Si. in its normal state [9] and for CePtzSi 2 [10]. Recently, we have studied CeCu5 which was identified as a Kondo lattice compound exhibiting antiRESULTS A N D DISCUSSION ferromagnetism below 4 K and a considerably high ~, value ( ~ 100mJmol -~ K -2) of the specific heat [11]. Figure 1 displays the electrical resistivity (Q) of Without changing the structure, CeCu4A1 which ~s the CeCu4AI as a function of temperature. A remarkable subject of this paper can be obtained from CeCu5 by feature of CeCu4A1 is its extremely high and nearly 271
272
N O N M A G N E T I C CeCu4Al C O M P O U N D
7~oI y ~Y?~2
Vol. 62, No. 4
80 70
120
CeCu~ AI
700
50 50
80 z,O
50
LaCu 4At
30
.0 20
20 ~0
7 IK] 5'o
100 '
150 '
2o 0
250 '
3b 0
"
r
O-
[,~] L
Fig. 1 The temperature dependence of the electrical reslstwity O of CeCu4A1 and LaCu4A1.
Fig 2 Om,g vs In T for CeCu4A1. 0m,g denotes the magnetic contribution to the electrical resistiwty.
temperature independent resistivity at elevated temperatures which is followed by a smooth, Kondo like Increase below 100K. It should be noted that a very similar 0(T) behaviour was found for CeCu6 [14], CeA13 [15] and CePt2SI 2 [10] which are known as nonmagnetic heavy fermion systems However maxima, followed by a sudden drop at low temperatures are visible in CeCu6 (Tin,, ~ 13K) [14], CeA13 (Tm~x ~ 35K) [15] and CePt2Si2 (Tmax ~ 75 K) [10] Usually, for temperatures T ,~ Tm,, the resistivity IS characterized by a T 2 dependence, which can be referred to quasiparticle scattering in a Fermi liquid. The coherence temperature T* marks the onset of this T 2 behavlour. In fact, this coherence temperature has been found experimentally in case of CeCu6 (To* ~ 0.1K) [16], CeAI3 (Tv* ~ 0.3K) [2] and CePt2Si2 (T* ~ 12 K) [10] Since the ofT) behavlour of CeCu4AI IS comparable to those of CeCu6, CeA13 and CePt2SI2 above their maximum temperature Tma,, we also expect the appearance of a maximum in this compound which would announce the region of coherent electron scattering processes If so, this Q(T) maximum exists below our lowest available temperature ( ~ 1.7 K). Because of the present unknown o(T) behaviour below 1 7 K it is not possible to estimate the coherence temperature To* of CeCu4A1, however T* is commonly found well below Tma,. To define the phonon-resistivity of CeCu4A1 we have measured the electrical resistivity of the isostructural nonmagnetic LaCu4A1 (see Fig. l). In Fig. 2 we have plotted the magnetic resistivity 0m,~ of CeCu4A1 [emag = 0(CeCu4 AI) -- 0(LaCu4Al)] in a semllogarithmlc representation. At sufficient low temperatures 0m,g(T) shows a logarithmic behaviour indicating K o n d o type interaction in the crystal field ground state. Well above the overall crystal field split-
tlng temperature a further logarithmic behaviour of 0m,g(T) should be visible [17]. This behavlour was found for CeCu4AI above 100 K The thermopower (S) of CeCu4AI as a function of temperature is drawn in Fig 3. S(T) of CeCu4A1 shows only a single maximum around 30K which amounts to about 10/W K ~. No negative values o r S were found between 4.2 and 300 K. Again, similarities are ascertainable to S(T) of the nonmagnetic heavy fermlon compounds CeCu6 [16] and CeAI~ above about 7 K [18]. The maximum of S(T) of CeCu6 was found at 60 K which corresponds with the first excited crystal field level of this compound [19]. In contrast, no such agreement between the crystal field splitting temperature and the thermopower maximum was found in CeA13 [20]. But in the case of CeAI3 a theoretical model developed by Bhattacharlee and Coqblin
s t/,v/Kl
T [K]
~0
7~0
i~0
2~0
2~0
300
-'--
Fig 3. The temperature dependence of the thermopower S of CeCu4A!
N O N M A G N E T I C CeCu4Al C O M P O U N D
Vol. 62, No. 4
tOi cp/ Ffd/m°teK2j O8
,¢p (]lmote~l 75 60 Z5 /
CeC.~At
30 15 o
,% ", ~ O~
/
,b 2b 3b ~ s, 83 " ~
CeCd6
O2 T2D~2]
Fig 4. A c,/T vs T 2 plot of the specific heat of CeCu4AI (e) together with those of CeCu6 (v). The inset shows the temperature dependence of the specific heat Cp of CeCu4A1 up to 60K. [21] which predicts the crystal field sphtting temperature in between 3 to 6 times of the thermopower maximum, fits very well. The rather high values of S(T) are obviously connected with high values of the derivative of the density-of-states at the Fermi level which agrees with the assumption of the formation of a strong resonance at the Fermi level. The specific heat (cp) of CeCu4AI is plolted in Fig. 4 as cp/T vs T 2. A carefully performed extrapolation of the high temperature part of this plot (6K < T < 15 K) yields a 7 value of about 280mJmol ~K ~- Below 6 K cp/T shows a strong increase, very slmdar to CeCu6 and CeAI~ For comparison we have measured the specific heat of CeCu6 whxch ls included in Fig. 4. The formaUon of a &p in the density-of-states near the Fermi level at T* should yield a decrease of %IT below this temperature [6]. While for CePt2SI2 a considerably high coherence temperature ( T* ~ 2 K) [10] was reported resulting in a mammum value of cp/Tof 1 2 0 m J m o l e K 2, the more lower T* values in CeCu2S12 ( ~ 0.5 K) [9], CeAI3 ( ~ 0 5 K) [8] and CeCu6 ( ~ 0.3 K) [7] are accompamed by strongly enhanced magmtudes of cp/T at low temperatures. W~thln this phenomenological picture the coherence temperature limits the maximum value of the specific heat c / T As can be expected from the much stronger increase of c / T vs T 2 in CeCu4A1 compared to CeCu6 or CeA13, and the supposed low coherence temperature T*, the data of Fig. 4 might notify an extremely high maximum value of ?(T) below 1.4K The inset in Fig. 4 shows the specific heat Cpas a function of temperature up to 60 K. A Schottky-type anomaly centered around 45 K seems to reflect the first excited crystal field sphtting level of about 90K. A similar value was deduced from specific heat measurements [22] as well
273
as from inelastic neutron scattering experiments [19] for CeCu 6. The substitution of A1 in CeCus, which increases the average conduction electron density, seems to be sufficient to screen all localized 4f-moments in CeCu4AI, which leads to a crossover from a magnetic ground state in CeCu5 to nonmagnetic ground state properties In CeCu4AI. This transition is expected from a magnetic phase diagram of Kondo compounds [5] if JD(E) (J. exchange energy, D(E). conduction electron density-of-states) exceeds a critical value {JD(E)},.
Acknowledgements - - We thank the "Hochschul]ubllaeumsstlftung der Stadt Wlen" for financial grant. Part of the work was supported by the "Fonds zur Foerderung der Wlssenschafthchen Forschung" (proJect number 6104). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9 10. 11. 12 13.
B. Barbara, J.X, Boucherle, J.L Buevoz, M.F. Rossignol & J Schweizer, Sohd State Commun. 24, 481 (1977). K. Andres, J.E. Graebner & H.R. Ott, Phys. Rev Letr 27, 1779 (1975). F. Steghch, J. Aarts, C.D. Bredl, W. Lleke, D. Meschede, W. Franz & H. Schaefer, Phys. Rev. Lett 43, 1892 (1979). J.M. Lawrence, P.S. Rlseborough & R.D. Parks, Rep. Prog. Phys. 44, 1 (1981). N.B. Brandt & V.V. Moshchalkov, Adv. Phys. 33, 373 (1974). C. Lacrolx, J. Mag. Mag. Mater 60, 145 (1986). T. Fujita, K. Satoh, Y Onuki & T. Komatsubara, J. Mag. Mag. Mater. 47--48, 66 (1985). G E. Brodale, R.A. Fisher, N.E. Philhps & J. Flouquet, Phys. Rev. Letr 56, 390 (1986). C.D. Bredl, S. Horn, F. Steglich, B. Luethl & R.M. Martin, Phys. Rev. Lett. 52, 1982 (1984) D. Gignoux, D. Schmitt, M. Zerguine, C. Ayache & E Bonjour, Physws Letr A l l 7 , 145 (1986). E. Bauer, E. Gratz & C. Schmitzer, to appear m J. Mag Mag. Mater. 63--64, (1987). T. Takeshita, S. Malik & W.E. Wallace, J. Sol. State Chem. 23, 225 (1978). S. Malik, W.E. Wallace & T. Takeshita, The
Rare Earths m Modern Science and Technology, 14. 15.
Vol 2 p. 347, (E&ted by G.J. McCarthy, J.J. Rhyne and H B. Sllber), Plenum Press (1980). H.R. Ott, H. Ru&gier, Z. Fisk, J.O. Wdlis & G.R. Stewart, Sohd State Commun. 53, 235 (1985). A. Pecheron, J.C. Achard, O. Gorochov, B. Cornut, D. Jerome & B. Coqblin, Solid State Commun. 12, 1289 (1973).
274 16.
NONMAGNETIC CeCu4AI COMPOUND
A. Amato, D. Jaccard, E. Walker & J. Flouquet, Solid State Commun. 55, 1131 (1985). 17. B. Cornut & B. Coqbhn, Phys. Rev. B5, 4541 (1972). 18. P.B van Aken, H.J. van Daal & H.J. Buschow, Proc. of the llth Rare Earth Research Conference, p. 738, Traverse City, Michigan (1974). 19. U. Walter, D. Wohlleben & Z. Fisk~ Z. Phys. B62, 235 (1986).
20. 21. 22.
Vol. 62, No. 4
A P. Muram, K. Knorr, K.H.J. Buschow, A. Benoit & J. Flouquet, Solid State Commun. 36, 523 (1980). A. Bhattacharjee & B. Coqbhn, Phys. Rev. B13, 3441 (1976). Y. Onukl, Y. Shlmlzu, T. Komatsubara, A. Sum~yama, Y. Oda, H. Nagano, T. Fujita, Y. Maeno, K. Satoh & T. Ohtsuka, J. Mag. Mag. Mater. 52, 325 (1985).
0038-1098/87 $3.00 + .00 Pergamon Journals Ltd.
H E A V Y F E R M I O N B E H A V I O U R O F T H E N O N M A G N E T I C CeCu4AI C O M P O U N D E. Bauer, E. Gratz and N. Plllmayr Institute of Experimental Physics, Technwal Umverslty Vienna, Austrm
(Recetved 22 October 1986 by P. Wachter) We present measurements of the temperature dependence of the electrical resistivity, the thermopower and the specific heat of the hexagonal compound CeCu4A1. At h~gh temperatures, the electrical resistivity is characterized by a nearly temperature independent behaviour, followed by a continuous increase below 100K. No maximum has been found down to 1.7 K. The thermopower shows a positive maximum at about 30 K. As in CeCu6 no negative values are observable in the range from 4.2 K up to a room temperature The specific heat data between 7 and 15K reveal a 7 value around 280mJ mol-Z K -2. Below this temperature range the specific heat cp/T shows a rapid rise and crosses the value of 1 J m o l - ~ K -2 at about 1.45 K. 1. I N T R O D U C T I O N
a substitution of one Cu-atom by an Al-atom. The whole family of the RECu4AI intermetalhcs (RE = rare earth) was found to crystallize in the hexagonal CaCu5 structure (P6/mmm) [12]. The substitution of Cu by A1 increases the average electron density per atom and therefore a significant change of the Kondo lattice behaviour of CeCu5 has to be expected. In order to investigate the variation of the physical properties depending on such a substitution we studied CeCu4A1. Polycrystalhne samples of CeCu4A1 and LaCu4AI were prepared by high frequency melting under argon atmosphere and subsequently annealed for 7 days at 600°C. The phase purity of the samples was checked by Debye-Scherrer photographs and by X-ray &ffractlon, usmg a conventional Siemens X-ray diffractometer. No traces of foreign phases were detected by these procedures. Electrical resistivity data were taken by means of a conventional four probe technique. The thermopower values were measured by a differential method, where Pb serves as reference material The specific heat was measured in a fully automated Nernst calorimeter. Previous measurements of the lattice constants (a = 5.195A, c = 4.188A) [12] as well as of the magnetic susceptibility [13] indicate a 3 + state for the Cerium ion in CeCunAI, within the uncertainty of such methods. The paramagnetic Curie temperature was found to lie at - 14 K.
IN R E C E N T YEARS growing interest has been focused on nearly trivalent Ce-based intermetallic compounds, whose unusual electronic properties are commonly referred to the existence of Kondo-type interaction. Among these properties, peculiar magnetic ordering with reduced moments as in CeAI2 [1], Fermiliquid behaviour as m CeA13 [2] or heavy fermlon superconductivity as in CeCu2Si2 [3] are of great experimental and theoretical relevance (for a revtew see e.g. [4, 5]). Within these Ce compounds the nonmagnetic CeA13 and C e f u 6 demonstrate the highest known 7 values of the specific heat ( ~ 1500mJ mol -~ K-2). This fact and most of the other physical properties have been attributed to the formation of a giant resonance at the Fermi-edge due to the anomalous proximity of the Ce 4 f level [5]. This resonance (Abrikosov-Suhl resonance, ASR) starts to increase strongly below a characteristic temperature, usually called the Kondo-temperature TK. The rise of the ASR ~s intimately connected to the increase of the 7 value at low temperatures. However, a modification of the ASR below a certain temperature T* (coherence temperature) is responsible for a drop of cp/T, giving rise to a maximum at T* [6]. Indeed, this behaviour was found for CeCu6 [7], for CeA13 [8], for CeCuz Si. in its normal state [9] and for CePtzSi 2 [10]. Recently, we have studied CeCu5 which was identified as a Kondo lattice compound exhibiting antiRESULTS A N D DISCUSSION ferromagnetism below 4 K and a considerably high ~, value ( ~ 100mJmol -~ K -2) of the specific heat [11]. Figure 1 displays the electrical resistivity (Q) of Without changing the structure, CeCu4A1 which ~s the CeCu4AI as a function of temperature. A remarkable subject of this paper can be obtained from CeCu5 by feature of CeCu4A1 is its extremely high and nearly 271
272
N O N M A G N E T I C CeCu4Al C O M P O U N D
7~oI y ~Y?~2
Vol. 62, No. 4
80 70
120
CeCu~ AI
700
50 50
80 z,O
50
LaCu 4At
30
.0 20
20 ~0
7 IK] 5'o
100 '
150 '
2o 0
250 '
3b 0
"
r
O-
[,~] L
Fig. 1 The temperature dependence of the electrical reslstwity O of CeCu4A1 and LaCu4A1.
Fig 2 Om,g vs In T for CeCu4A1. 0m,g denotes the magnetic contribution to the electrical resistiwty.
temperature independent resistivity at elevated temperatures which is followed by a smooth, Kondo like Increase below 100K. It should be noted that a very similar 0(T) behaviour was found for CeCu6 [14], CeA13 [15] and CePt2SI 2 [10] which are known as nonmagnetic heavy fermion systems However maxima, followed by a sudden drop at low temperatures are visible in CeCu6 (Tin,, ~ 13K) [14], CeA13 (Tm~x ~ 35K) [15] and CePt2Si2 (Tmax ~ 75 K) [10] Usually, for temperatures T ,~ Tm,, the resistivity IS characterized by a T 2 dependence, which can be referred to quasiparticle scattering in a Fermi liquid. The coherence temperature T* marks the onset of this T 2 behavlour. In fact, this coherence temperature has been found experimentally in case of CeCu6 (To* ~ 0.1K) [16], CeAI3 (Tv* ~ 0.3K) [2] and CePt2Si2 (T* ~ 12 K) [10] Since the ofT) behavlour of CeCu4AI IS comparable to those of CeCu6, CeA13 and CePt2SI2 above their maximum temperature Tma,, we also expect the appearance of a maximum in this compound which would announce the region of coherent electron scattering processes If so, this Q(T) maximum exists below our lowest available temperature ( ~ 1.7 K). Because of the present unknown o(T) behaviour below 1 7 K it is not possible to estimate the coherence temperature To* of CeCu4A1, however T* is commonly found well below Tma,. To define the phonon-resistivity of CeCu4A1 we have measured the electrical resistivity of the isostructural nonmagnetic LaCu4A1 (see Fig. l). In Fig. 2 we have plotted the magnetic resistivity 0m,~ of CeCu4A1 [emag = 0(CeCu4 AI) -- 0(LaCu4Al)] in a semllogarithmlc representation. At sufficient low temperatures 0m,g(T) shows a logarithmic behaviour indicating K o n d o type interaction in the crystal field ground state. Well above the overall crystal field split-
tlng temperature a further logarithmic behaviour of 0m,g(T) should be visible [17]. This behavlour was found for CeCu4AI above 100 K The thermopower (S) of CeCu4AI as a function of temperature is drawn in Fig 3. S(T) of CeCu4A1 shows only a single maximum around 30K which amounts to about 10/W K ~. No negative values o r S were found between 4.2 and 300 K. Again, similarities are ascertainable to S(T) of the nonmagnetic heavy fermlon compounds CeCu6 [16] and CeAI~ above about 7 K [18]. The maximum of S(T) of CeCu6 was found at 60 K which corresponds with the first excited crystal field level of this compound [19]. In contrast, no such agreement between the crystal field splitting temperature and the thermopower maximum was found in CeA13 [20]. But in the case of CeAI3 a theoretical model developed by Bhattacharlee and Coqblin
s t/,v/Kl
T [K]
~0
7~0
i~0
2~0
2~0
300
-'--
Fig 3. The temperature dependence of the thermopower S of CeCu4A!
N O N M A G N E T I C CeCu4Al C O M P O U N D
Vol. 62, No. 4
tOi cp/ Ffd/m°teK2j O8
,¢p (]lmote~l 75 60 Z5 /
CeC.~At
30 15 o
,% ", ~ O~
/
,b 2b 3b ~ s, 83 " ~
CeCd6
O2 T2D~2]
Fig 4. A c,/T vs T 2 plot of the specific heat of CeCu4AI (e) together with those of CeCu6 (v). The inset shows the temperature dependence of the specific heat Cp of CeCu4A1 up to 60K. [21] which predicts the crystal field sphtting temperature in between 3 to 6 times of the thermopower maximum, fits very well. The rather high values of S(T) are obviously connected with high values of the derivative of the density-of-states at the Fermi level which agrees with the assumption of the formation of a strong resonance at the Fermi level. The specific heat (cp) of CeCu4AI is plolted in Fig. 4 as cp/T vs T 2. A carefully performed extrapolation of the high temperature part of this plot (6K < T < 15 K) yields a 7 value of about 280mJmol ~K ~- Below 6 K cp/T shows a strong increase, very slmdar to CeCu6 and CeAI~ For comparison we have measured the specific heat of CeCu6 whxch ls included in Fig. 4. The formaUon of a &p in the density-of-states near the Fermi level at T* should yield a decrease of %IT below this temperature [6]. While for CePt2SI2 a considerably high coherence temperature ( T* ~ 2 K) [10] was reported resulting in a mammum value of cp/Tof 1 2 0 m J m o l e K 2, the more lower T* values in CeCu2S12 ( ~ 0.5 K) [9], CeAI3 ( ~ 0 5 K) [8] and CeCu6 ( ~ 0.3 K) [7] are accompamed by strongly enhanced magmtudes of cp/T at low temperatures. W~thln this phenomenological picture the coherence temperature limits the maximum value of the specific heat c / T As can be expected from the much stronger increase of c / T vs T 2 in CeCu4A1 compared to CeCu6 or CeA13, and the supposed low coherence temperature T*, the data of Fig. 4 might notify an extremely high maximum value of ?(T) below 1.4K The inset in Fig. 4 shows the specific heat Cpas a function of temperature up to 60 K. A Schottky-type anomaly centered around 45 K seems to reflect the first excited crystal field sphtting level of about 90K. A similar value was deduced from specific heat measurements [22] as well
273
as from inelastic neutron scattering experiments [19] for CeCu 6. The substitution of A1 in CeCus, which increases the average conduction electron density, seems to be sufficient to screen all localized 4f-moments in CeCu4AI, which leads to a crossover from a magnetic ground state in CeCu5 to nonmagnetic ground state properties In CeCu4AI. This transition is expected from a magnetic phase diagram of Kondo compounds [5] if JD(E) (J. exchange energy, D(E). conduction electron density-of-states) exceeds a critical value {JD(E)},.
Acknowledgements - - We thank the "Hochschul]ubllaeumsstlftung der Stadt Wlen" for financial grant. Part of the work was supported by the "Fonds zur Foerderung der Wlssenschafthchen Forschung" (proJect number 6104). REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9 10. 11. 12 13.
B. Barbara, J.X, Boucherle, J.L Buevoz, M.F. Rossignol & J Schweizer, Sohd State Commun. 24, 481 (1977). K. Andres, J.E. Graebner & H.R. Ott, Phys. Rev Letr 27, 1779 (1975). F. Steghch, J. Aarts, C.D. Bredl, W. Lleke, D. Meschede, W. Franz & H. Schaefer, Phys. Rev. Lett 43, 1892 (1979). J.M. Lawrence, P.S. Rlseborough & R.D. Parks, Rep. Prog. Phys. 44, 1 (1981). N.B. Brandt & V.V. Moshchalkov, Adv. Phys. 33, 373 (1974). C. Lacrolx, J. Mag. Mag. Mater 60, 145 (1986). T. Fujita, K. Satoh, Y Onuki & T. Komatsubara, J. Mag. Mag. Mater. 47--48, 66 (1985). G E. Brodale, R.A. Fisher, N.E. Philhps & J. Flouquet, Phys. Rev. Letr 56, 390 (1986). C.D. Bredl, S. Horn, F. Steglich, B. Luethl & R.M. Martin, Phys. Rev. Lett. 52, 1982 (1984) D. Gignoux, D. Schmitt, M. Zerguine, C. Ayache & E Bonjour, Physws Letr A l l 7 , 145 (1986). E. Bauer, E. Gratz & C. Schmitzer, to appear m J. Mag Mag. Mater. 63--64, (1987). T. Takeshita, S. Malik & W.E. Wallace, J. Sol. State Chem. 23, 225 (1978). S. Malik, W.E. Wallace & T. Takeshita, The
Rare Earths m Modern Science and Technology, 14. 15.
Vol 2 p. 347, (E&ted by G.J. McCarthy, J.J. Rhyne and H B. Sllber), Plenum Press (1980). H.R. Ott, H. Ru&gier, Z. Fisk, J.O. Wdlis & G.R. Stewart, Sohd State Commun. 53, 235 (1985). A. Pecheron, J.C. Achard, O. Gorochov, B. Cornut, D. Jerome & B. Coqblin, Solid State Commun. 12, 1289 (1973).
274 16.
NONMAGNETIC CeCu4AI COMPOUND
A. Amato, D. Jaccard, E. Walker & J. Flouquet, Solid State Commun. 55, 1131 (1985). 17. B. Cornut & B. Coqbhn, Phys. Rev. B5, 4541 (1972). 18. P.B van Aken, H.J. van Daal & H.J. Buschow, Proc. of the llth Rare Earth Research Conference, p. 738, Traverse City, Michigan (1974). 19. U. Walter, D. Wohlleben & Z. Fisk~ Z. Phys. B62, 235 (1986).
20. 21. 22.
Vol. 62, No. 4
A P. Muram, K. Knorr, K.H.J. Buschow, A. Benoit & J. Flouquet, Solid State Commun. 36, 523 (1980). A. Bhattacharjee & B. Coqbhn, Phys. Rev. B13, 3441 (1976). Y. Onukl, Y. Shlmlzu, T. Komatsubara, A. Sum~yama, Y. Oda, H. Nagano, T. Fujita, Y. Maeno, K. Satoh & T. Ohtsuka, J. Mag. Mag. Mater. 52, 325 (1985).