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Electrical resistivity of the intermediate valence compound CePd3 under hydrostatic pressure
Solid State Communications, Vol. 55, No. 2, pp. 179-181, 1985. Printed in Great Britain.
0038-1098/85 $3.00 + .00 Pergamon Press Ltd.
ELECTRICAL RESISTIVITY OF THE INTERMEDIATE VALENCE COMPOUND CePd3 UNDER HYDROSTATIC PRESSURE J. Beille, B. Cheaito, A. Draperi, R.M. Galera and J. Pierre Laboratoire Louis N6el, C.N.R.S., 166X, 38042 Grenoble-codex, France (Received 6 March 1985 by E.F. Bertaut) The electrical resistivity of CePd3 has been measured between 1.5 and 300 K under hydrostatic pressures up to 20 kbar. The temperature TM for the maximum of resistivity increases with pressure at the rate dTM[dp = 0.65 Kkbar -1 . The v a l u e , - 5.2, found for a In TM[a In V is in good agreement with previous data based on elasticity measurements and thermodynamical properties. and the resistivity at 300 K have only a weak variation for pressures up to 20 kbar. With increasing pressure, the maximum in the resistivity shifts to higher temperatures and we observe a small significant decrease in the resistivity value at the maximum (Fig. 2). This result was previously observed by Mignot and Wittig [3] under very high pressure. Nevertheless those measurements were made on powder samples and it was difficult to separate the compacting effects and the geometrical factor change from the intrinsic effects. Moreover, the absolute value of the resistivity could not be determined. In the present experiment, the temperature corresponding to the resistivity anomaly, TM, increases linearly with pressure up to 20 kbar, while the resistivity amplitude, PM, decreases linearly (Fig. 3). The pressure derivatives are:
CERIUM INTERMETALLIC COMPOUNDS and cerium metal exhibit anomalous physical properties and are generally classified either as Kondo or as intermediate valence type. In intermediate valence systems the cerium fluctuates between two configurations 4/'1 and 4./"°, contrary to the Kondo systems in which the cerium valence is well-defined (v = 3). Experimental results show that in such compounds the pressure is an important parameter, the best known pressure effect being the 7---a phase transition in cerium metal under 7kbar. Therefore high pressure measurements appear as a powerful method for the study of anomalous rare earth systems. We present here the temperature dependence of the electrical resistivity of CePd3 measured under hydrostatic pressures up to 20 kbar. EXPERIMENTS The electrical resistivity has been measured on a bulk polycrystalline sample (2.5 mm x 0.5 mm x 0.5 mm), using a four probe method. Pressure was generated in a hydrostatic type beryllium copper self-clamped vessel, The sample was pressurised inside a teflon capsule by a 50:50 pentane-isoamyl alcohol mixture. The value of the pressure is derived from the superconductive transition of lead [1]. At 20kbar, the uncertainty of the pressure is about + 500 bar.
dTM dp - 0.65 -+ 0.2 K.kbar -1, and dr dp -
with r = (PM--Po)/(P3oo--Po), 03oo and Po are the room temperature and the residual resistivity of the sample respectively. From the bulk modulus of the sample (B = 10.25 10 s bar) [4] we deduce:
RESULTS The electrical resistivity of CePda at normal pressure presents a very unusual behaviour (Fig. 1). It first increases from the low temperatures to a maximum at about 130K and then slowly decreases up to 300K. The weak value of the residual resistivity at T = 0 K, shows that disorder and impurity contributions are relatively small [2]. Under pressure, the shape of the resistivity curve is not modified. The residual resistivity
1.45 -+ 0.15 kbar -1 ,
a In TM aln V
-
-- 5.2
and
a lnr - - = aln V
1.1.
A linear extrapolation would give TM = 300 K for P = 260kbar and r = I for P = 240kbar. This agrees with the fact that the anomaly has been found to disappear in the region of about 200 kbar [3].
179
180
CePd3 UNDER HYDROSTATIC PRESSURE
Vol. 55, No. 2
200
Ce Pd3
0 0
I00
-
/
(~) P (borX~
7650 12200
(')
16800
(,) t 9 5 o o
I
0
I
I O0
300
200
TemperGture (K)
Fig. 1. Temperature dependence of the resistivity of CePd3 under various pressures. 180
The anomaly of the resistivity and the maximum in the magnetic susceptibility in CePda occur at about the same temperature (= 130 K) and above this temperature the susceptibility follows a Curie-Weiss law. This may correspond to the cross-over between magnetic and non magnetic behaviour, related to both, thermal population of the magnetic configuration and decrease of E e with increasing temperature. The progressive shift towards the high temperatures and the amplitude decrease of the resistivity anomaly in CePda clearly indicate that the pressure favours the non magnetic state. We cannot theoretically relate T~ and E c .
Ce Pd3
•
:..'
: 160
P
0 •
E
• ;, = '
@)
o
(.)
7650
P(bor) (e)
12200
• ~, > ~
• "' 140
(.) t 6 8 0 0
:l=
D
:'~,
(z)
19500
145
~•lp •
1.56
~=• x
Ce Pd3
ot 120
*A z
5O
I
I O0
I
150
200
140
Temperoture (K)
0
Fig. 2. Temperature dependence of the resistivity of CePd3 in the vicinity of the maximum. DISCUSSION In a recent theoretical work for I.V. systems Ramakrishnan and Sur [5] predict the existence of a non magnetic ground state (Energy Eo) and an excited magnetic configuration (El), with an energy splitting Ee = Er -- Eo, E : being renormalized with temperature. In agreement with theoretical predictions, neutron measurements on CePd3 [6] have revealed the existence, at low temperatures, of an inelastic magnetic excitation at E e = 700 K. This excitation disappears into a large quasielastic structure at 300 K.
A V
'8 1.34
135
I.I :E
130
12~ = 0
I 5
I I0
I 15
1.32 20
Pressure (k bor)
Fig. 3. Pressure dependence of the temperature at the maximum of resistivity, TM, and of r = ( P M - - P o ) /
6o30o-po).
Vol. 55, No. 2
CePds UNDER HYDROSTATIC PRESSURE
181
Takke et al. [4] however have introduced an elec- variation with volume is expected. To verify this statetronic Griineisen parameter I2g with I2g = ~ In Te/~ In V. ment we intend to measure the magnetic susceptibilities Te is the characteristic temperature of the I.V. systems under pressure. which could be taken as E e. In CePds, they determine Acknowledgements - We would like to thank Dr. D. from the thermal expansion and the specific heat a low Givord for his critical reading of the manuscript. We are temperature ( T ~ TM) Grtineisen parameter ~2g = 10. also grateful to S. Pelosi for his very efficient technical Their calculation of the temperature dependence of the assistance on the high pressure equipments. bulk modulus, assuming a constant ~2g = 10, is in a very good agreement with experimental data for REFERENCES T < 220K. In CeSna, ~2g could be determined more precisely. It is found to decrease from 10 at low tem- 1. A. Eiling & J.S. Schilling, J. Phys. F: Metal Phys., 11 623 (1981). peratures to about 5 near TM. A similar behaviour may 2. H. Schneider & D.K. Wohlleben, Z. Phys. Bbe expected in CePds. Condensed Matter, 44 193 (1981), M.J. Besnus, If we consider that E e and TM vary in the same J.P. Kappler & A. Meyer J. Phys. F: Metal Phys., way with pressure, our data for a In TM/~ In V can be 13 597 (1983). a direct measurement of -- ~2g. This is confirmed by the 3. J.M. Mignot & J. Wittig, in Physics o f Solid under High Pressure (edited by J.S. Schilling & R.N. fact that ~ In TM/~ In V is in good agreement with the Shelton), North-Holland Publishing Co, 311 value of -- ~2g calculated by Takke et al., (taking into (1981). account the approximations of the thermodynamical 4. R. Takke, M. Niksch, W. Assmus, B. Ltithi, R. Pott, model). R. Schefzyk & D.K. Wohlleben, Z. Phys. B ConThus the resistivity measurements under hydrostatic densed Matter, 44 3339 (1981). T.V. Ramakrishnan & K. Sur, Phys. Rev. B, 26 pressure in the 20kbar range seem to be a very good 5. 1782 (1982). method for the direct determination of the characteristic 6. R.M. Galera, D. Givord, A.P. Murani, J. Pierre, energy variation with pressure of CePds. In theoretical C. Vettier & K.R.A. Ziebeck, in Valence Instamodels [5] for I.V. systems the magnetic susceptibility bilities, Proc. of the 4th Intern. Conf., Cologne is also related to the characteristic energy and the same (1984).
0038-1098/85 $3.00 + .00 Pergamon Press Ltd.
ELECTRICAL RESISTIVITY OF THE INTERMEDIATE VALENCE COMPOUND CePd3 UNDER HYDROSTATIC PRESSURE J. Beille, B. Cheaito, A. Draperi, R.M. Galera and J. Pierre Laboratoire Louis N6el, C.N.R.S., 166X, 38042 Grenoble-codex, France (Received 6 March 1985 by E.F. Bertaut) The electrical resistivity of CePd3 has been measured between 1.5 and 300 K under hydrostatic pressures up to 20 kbar. The temperature TM for the maximum of resistivity increases with pressure at the rate dTM[dp = 0.65 Kkbar -1 . The v a l u e , - 5.2, found for a In TM[a In V is in good agreement with previous data based on elasticity measurements and thermodynamical properties. and the resistivity at 300 K have only a weak variation for pressures up to 20 kbar. With increasing pressure, the maximum in the resistivity shifts to higher temperatures and we observe a small significant decrease in the resistivity value at the maximum (Fig. 2). This result was previously observed by Mignot and Wittig [3] under very high pressure. Nevertheless those measurements were made on powder samples and it was difficult to separate the compacting effects and the geometrical factor change from the intrinsic effects. Moreover, the absolute value of the resistivity could not be determined. In the present experiment, the temperature corresponding to the resistivity anomaly, TM, increases linearly with pressure up to 20 kbar, while the resistivity amplitude, PM, decreases linearly (Fig. 3). The pressure derivatives are:
CERIUM INTERMETALLIC COMPOUNDS and cerium metal exhibit anomalous physical properties and are generally classified either as Kondo or as intermediate valence type. In intermediate valence systems the cerium fluctuates between two configurations 4/'1 and 4./"°, contrary to the Kondo systems in which the cerium valence is well-defined (v = 3). Experimental results show that in such compounds the pressure is an important parameter, the best known pressure effect being the 7---a phase transition in cerium metal under 7kbar. Therefore high pressure measurements appear as a powerful method for the study of anomalous rare earth systems. We present here the temperature dependence of the electrical resistivity of CePd3 measured under hydrostatic pressures up to 20 kbar. EXPERIMENTS The electrical resistivity has been measured on a bulk polycrystalline sample (2.5 mm x 0.5 mm x 0.5 mm), using a four probe method. Pressure was generated in a hydrostatic type beryllium copper self-clamped vessel, The sample was pressurised inside a teflon capsule by a 50:50 pentane-isoamyl alcohol mixture. The value of the pressure is derived from the superconductive transition of lead [1]. At 20kbar, the uncertainty of the pressure is about + 500 bar.
dTM dp - 0.65 -+ 0.2 K.kbar -1, and dr dp -
with r = (PM--Po)/(P3oo--Po), 03oo and Po are the room temperature and the residual resistivity of the sample respectively. From the bulk modulus of the sample (B = 10.25 10 s bar) [4] we deduce:
RESULTS The electrical resistivity of CePda at normal pressure presents a very unusual behaviour (Fig. 1). It first increases from the low temperatures to a maximum at about 130K and then slowly decreases up to 300K. The weak value of the residual resistivity at T = 0 K, shows that disorder and impurity contributions are relatively small [2]. Under pressure, the shape of the resistivity curve is not modified. The residual resistivity
1.45 -+ 0.15 kbar -1 ,
a In TM aln V
-
-- 5.2
and
a lnr - - = aln V
1.1.
A linear extrapolation would give TM = 300 K for P = 260kbar and r = I for P = 240kbar. This agrees with the fact that the anomaly has been found to disappear in the region of about 200 kbar [3].
179
180
CePd3 UNDER HYDROSTATIC PRESSURE
Vol. 55, No. 2
200
Ce Pd3
0 0
I00
-
/
(~) P (borX~
7650 12200
(')
16800
(,) t 9 5 o o
I
0
I
I O0
300
200
TemperGture (K)
Fig. 1. Temperature dependence of the resistivity of CePd3 under various pressures. 180
The anomaly of the resistivity and the maximum in the magnetic susceptibility in CePda occur at about the same temperature (= 130 K) and above this temperature the susceptibility follows a Curie-Weiss law. This may correspond to the cross-over between magnetic and non magnetic behaviour, related to both, thermal population of the magnetic configuration and decrease of E e with increasing temperature. The progressive shift towards the high temperatures and the amplitude decrease of the resistivity anomaly in CePda clearly indicate that the pressure favours the non magnetic state. We cannot theoretically relate T~ and E c .
Ce Pd3
•
:..'
: 160
P
0 •
E
• ;, = '
@)
o
(.)
7650
P(bor) (e)
12200
• ~, > ~
• "' 140
(.) t 6 8 0 0
:l=
D
:'~,
(z)
19500
145
~•lp •
1.56
~=• x
Ce Pd3
ot 120
*A z
5O
I
I O0
I
150
200
140
Temperoture (K)
0
Fig. 2. Temperature dependence of the resistivity of CePd3 in the vicinity of the maximum. DISCUSSION In a recent theoretical work for I.V. systems Ramakrishnan and Sur [5] predict the existence of a non magnetic ground state (Energy Eo) and an excited magnetic configuration (El), with an energy splitting Ee = Er -- Eo, E : being renormalized with temperature. In agreement with theoretical predictions, neutron measurements on CePd3 [6] have revealed the existence, at low temperatures, of an inelastic magnetic excitation at E e = 700 K. This excitation disappears into a large quasielastic structure at 300 K.
A V
'8 1.34
135
I.I :E
130
12~ = 0
I 5
I I0
I 15
1.32 20
Pressure (k bor)
Fig. 3. Pressure dependence of the temperature at the maximum of resistivity, TM, and of r = ( P M - - P o ) /
6o30o-po).
Vol. 55, No. 2
CePds UNDER HYDROSTATIC PRESSURE
181
Takke et al. [4] however have introduced an elec- variation with volume is expected. To verify this statetronic Griineisen parameter I2g with I2g = ~ In Te/~ In V. ment we intend to measure the magnetic susceptibilities Te is the characteristic temperature of the I.V. systems under pressure. which could be taken as E e. In CePds, they determine Acknowledgements - We would like to thank Dr. D. from the thermal expansion and the specific heat a low Givord for his critical reading of the manuscript. We are temperature ( T ~ TM) Grtineisen parameter ~2g = 10. also grateful to S. Pelosi for his very efficient technical Their calculation of the temperature dependence of the assistance on the high pressure equipments. bulk modulus, assuming a constant ~2g = 10, is in a very good agreement with experimental data for REFERENCES T < 220K. In CeSna, ~2g could be determined more precisely. It is found to decrease from 10 at low tem- 1. A. Eiling & J.S. Schilling, J. Phys. F: Metal Phys., 11 623 (1981). peratures to about 5 near TM. A similar behaviour may 2. H. Schneider & D.K. Wohlleben, Z. Phys. Bbe expected in CePds. Condensed Matter, 44 193 (1981), M.J. Besnus, If we consider that E e and TM vary in the same J.P. Kappler & A. Meyer J. Phys. F: Metal Phys., way with pressure, our data for a In TM/~ In V can be 13 597 (1983). a direct measurement of -- ~2g. This is confirmed by the 3. J.M. Mignot & J. Wittig, in Physics o f Solid under High Pressure (edited by J.S. Schilling & R.N. fact that ~ In TM/~ In V is in good agreement with the Shelton), North-Holland Publishing Co, 311 value of -- ~2g calculated by Takke et al., (taking into (1981). account the approximations of the thermodynamical 4. R. Takke, M. Niksch, W. Assmus, B. Ltithi, R. Pott, model). R. Schefzyk & D.K. Wohlleben, Z. Phys. B ConThus the resistivity measurements under hydrostatic densed Matter, 44 3339 (1981). T.V. Ramakrishnan & K. Sur, Phys. Rev. B, 26 pressure in the 20kbar range seem to be a very good 5. 1782 (1982). method for the direct determination of the characteristic 6. R.M. Galera, D. Givord, A.P. Murani, J. Pierre, energy variation with pressure of CePds. In theoretical C. Vettier & K.R.A. Ziebeck, in Valence Instamodels [5] for I.V. systems the magnetic susceptibility bilities, Proc. of the 4th Intern. Conf., Cologne is also related to the characteristic energy and the same (1984).