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Magnetic and structural phase transition of CeAg at hydrostatic pressure
Volume 70A, number 5,6
PHYSICS LETTERS
2 April 1979
MAGNETIC AND STRUCTURAL PHASE TRANSITION OF CeAg AT HYDROSTATIC PRESSURE 1-lideoki KADOMATSU, Makio KURISU and Hiroshi FUJIWARA Faculty of Science, Hiroshima University, hiroshima, 730, Japan Received 8 November 1978
Pressure effects on the Curie temperature and the crystallographic phase transition temperature of CeAg were determined from an electrical resistivity measurement from 4.2 to 300 K at hydrostatic pressures up to 5 kb. Results correspond to the alloying effect in Ce(Ag,ln).
Among the equiatomic intermetallic compounds, with CsCl structure at room temperature, of rare earth elements and silver, only CeAg is ferronrngnetic with Curie temperature Tc = 6—9 K 11—3] and its origin is actively investigated. Moreover, there is a crystallographic phase transition temperature TM at 15 K from the cubic to the tetragonal structure. This transition has been considered to be martensitic and to result from a Jahn—Teller effect, suggesting strongly that the Fermi energy level of CeAg lies close to the peak position in a region of high density of states [4,5]. Therefore, information on the variation of Tc or TM with a change in the Fermi energy level will be required. Regarding this subject, Ihrig and Lohmann [3] quite recently carried out investigations from the standpoint of the alloying effect, by substituting Ag with In such as CeAg~In1_~. Under these circumstances, the present work has been started for the purpose of investigating the same subject in more detail, but from the standpoint of the pressure effect. This paper concerns the hydrostatic pressure effects on T~ and TM determined from measurement of the electrical resistivity of CeAg at pressures up to 5 kb in the temperature range from 4.2 to 300 K. The compound was prepared from 99.9% Ce and 99.999% Ag by melting in a plasma jet furnace in an argon atmosphere. An ingot was turned over, remelted several times and then was sealed in an evacuated quartz tube, subjected to a homogenizing annealing at 500°Cfor one week. The preparation was made extremely carefully to prevent oxidation. The total 472
weight loss was less than 0.01%. An X-ray analysis at room temperature revealed the CsCl-type crystal structure. The specimen was made with a rectangular shape and a maximum dimension of about 10mm. The cutting was carried out in mineral oil, followed by the annealing at 500°C for 24 hours. The electrical resistivity was measured by means of the four-terminal method and the electrical leads of Cu wires were connected to the specimen by spot welding. A Be—Cu clamp cell equipped with an armored 0-ring seal generated pressures up to 5 kb near 4.2 K and the pressure was transmitted hydrostatically to the specimen and to the superconducting manometer (Sn) through spindle oil. The conversion of the manometer data into pressure values has been based on the relation between the superconducting transition temperature and pressure for Sn. The pressure actually applied in the present operating temperature range up to about 150 K may be slightly higher than that measured at 3.7 K, due to a slight loss resulting from the cooling procedure. The influence of this loss, however, is very small. Another loss occurs when the spindle oil freezes, but the freezing temperature is beyond the maximum operation temperature. Fig. 1 gives the isobar data on the electrical resistivity p in a temperature range from 4.2 up to 150 K. In the figure, the pressures actually used were in the order 0, 2.4, 4.4, 1 .8, 0 and 4.9 kb. Detailed and magnified information at lower temperatures is plotted in fig. 2, where the pressures quoted from fig. 1 are 0, 2.4 and 4.9 kb. As indicated by arrows in fig. 2, Tc at
Volume 70A, number 5,6
PHYSICS LETTERS
I
I
2 April 1979
8 I
_____
30
P1 kb)
~
I
7
150
/
oo~
°
~
50
/ ~
20
///\~‘
—
P1kb)
4
5
6°
//J-~j.8~
/
I0•
//
Fig. 3. Pressure dependence of T~and TM for CeAg.
/
0
/
,1 I
0
50
I
T (K)
100
150
[2, 3] is satisfactory. (ii) As was expected, the hysteresis phenomenon appears around TM as in fig. 1, when the resistivity measurement was carried out under pressures. But no hysteresis was found, as in fig. 2, at T~. (iii) The measurements were completely reversible in magnitude: the values of Tc, TM and p before and
at various pressures.
after pressure application were the same. This fact may substantiate the circumstance that the applied pressure is hydrostatic and/or the magnetic properties
each pressure was uniquely determined. On the other hand, TM in the present work was defined as the ternperature corresponding to the center of the width of the hysteresis in fig. 1. The clear and important results obtained are summarized as follows. (i) The values of T~and TM at normal pressure were 5.5 and 16 K, respectively, and
of the specimen are reversible in pressure. The variation of T~and TM with pressure is shown in fig. 3, where the data on T~and TM should be read with left-hand and right-hand scales in the ordinate, respectively. The vertical bars in the plot of TM represent the width of the hysteresis in fig. 1. The summarized results are as follows. (i) The variation of T~and TM with pressure is not necessarily linear. Although both
the agreement of these values with the published data
transition temperatures increase with increasing pres-
Fig. 1. The electrical resistivity of CeAg versus temperature
sure, the variation is rather concave downward for T~ I
I
P4.9kb
______
6
1
1
~
in this pressure effect are the same as those in the case of the alloying effect in CeAg~In~~[3]. (i~Frnm
the curves in fig. 3. The results thus obtained are.
C
..‘
and almost linear for TM up to about 4 kb, suggesting a rapid increase at higher pressures. The trends found~
2
P=
z~T~/~p+ 0.4 deg/kb and z~TM/z~p + 20 deg/kb.
0kb
No available data have been found on the pressure 0
—~-~
4
5
6
7
8
9
I0
II
Fig. 2. The electrical resistivity of CeAg versus temperature near Te at various pressures.
effect on Te and TM for CeAg, but the value of L~TMfL~p in the present work agrees very well with the result of ~TM/~p obtained for LaAg [6]. (iii) So far as the temperature range operated is concerned, the resistivity p at a given temperature increases with pres473
Volume 70A number 5,6
PHYSICS LETTERS
2 April 1979
sure. A quantitative evaluation of zip/p, however, should be made with the compressibility data.
In conclusion, the pressure effects on T~and TM in the present work likely reflect the result of the alloy-
In the course of discussing the alloying effect on Tc and TM of CeAg, it has been pointed out [3] that the most important factors are the location of the Fermi energy level relative to the high density of states and the shift of the level associated with the Jahn—Teller distortion. This way of analysis may be applicable to the results of the pressure effects on T~,TM and p which were carried out in the present work. The increase in Tc with pressure suggests an enhancement of the s—f exchange interaction resulting from an upward shift of the Fermi energy level with pressure. The fact that both zXTM/~pand z~TM/1~c, where c is the concentration of substituted element In in the alloy-
ing effect and will be a more direct way to further investigate the electronic structure than the alloying effect. Details will be reported in the near future.
ing effect, are positive may support a situation in which the distortion due to pressure may be in the same direction as that due to the Jahn—Teller distortion.
474
References [11 R.E.
Walline and W.E. Wallace, J. Chem. Phys. 41(1964)
3285. [21 D. Schmitt, P. Morjn and J. Pierre, J. Magn. Magn. Mat. 8 249. 131 (1978) II. lhrig and W. Lohmann, J. Phys. Fl (1977) 1957. [41 A. Hasegawa, B. Bremicker and J. Kübler, Z. Phys. B22
(1975) 231.
151 D.K.
Ray and J. Sivardiere, Solid State Commun. 19
(1976) 1053.
L6l J.S. Schilling, S. Methfessel and State Commun. 24 (1977) 659.
R.N. Shelton, Solid
PHYSICS LETTERS
2 April 1979
MAGNETIC AND STRUCTURAL PHASE TRANSITION OF CeAg AT HYDROSTATIC PRESSURE 1-lideoki KADOMATSU, Makio KURISU and Hiroshi FUJIWARA Faculty of Science, Hiroshima University, hiroshima, 730, Japan Received 8 November 1978
Pressure effects on the Curie temperature and the crystallographic phase transition temperature of CeAg were determined from an electrical resistivity measurement from 4.2 to 300 K at hydrostatic pressures up to 5 kb. Results correspond to the alloying effect in Ce(Ag,ln).
Among the equiatomic intermetallic compounds, with CsCl structure at room temperature, of rare earth elements and silver, only CeAg is ferronrngnetic with Curie temperature Tc = 6—9 K 11—3] and its origin is actively investigated. Moreover, there is a crystallographic phase transition temperature TM at 15 K from the cubic to the tetragonal structure. This transition has been considered to be martensitic and to result from a Jahn—Teller effect, suggesting strongly that the Fermi energy level of CeAg lies close to the peak position in a region of high density of states [4,5]. Therefore, information on the variation of Tc or TM with a change in the Fermi energy level will be required. Regarding this subject, Ihrig and Lohmann [3] quite recently carried out investigations from the standpoint of the alloying effect, by substituting Ag with In such as CeAg~In1_~. Under these circumstances, the present work has been started for the purpose of investigating the same subject in more detail, but from the standpoint of the pressure effect. This paper concerns the hydrostatic pressure effects on T~ and TM determined from measurement of the electrical resistivity of CeAg at pressures up to 5 kb in the temperature range from 4.2 to 300 K. The compound was prepared from 99.9% Ce and 99.999% Ag by melting in a plasma jet furnace in an argon atmosphere. An ingot was turned over, remelted several times and then was sealed in an evacuated quartz tube, subjected to a homogenizing annealing at 500°Cfor one week. The preparation was made extremely carefully to prevent oxidation. The total 472
weight loss was less than 0.01%. An X-ray analysis at room temperature revealed the CsCl-type crystal structure. The specimen was made with a rectangular shape and a maximum dimension of about 10mm. The cutting was carried out in mineral oil, followed by the annealing at 500°C for 24 hours. The electrical resistivity was measured by means of the four-terminal method and the electrical leads of Cu wires were connected to the specimen by spot welding. A Be—Cu clamp cell equipped with an armored 0-ring seal generated pressures up to 5 kb near 4.2 K and the pressure was transmitted hydrostatically to the specimen and to the superconducting manometer (Sn) through spindle oil. The conversion of the manometer data into pressure values has been based on the relation between the superconducting transition temperature and pressure for Sn. The pressure actually applied in the present operating temperature range up to about 150 K may be slightly higher than that measured at 3.7 K, due to a slight loss resulting from the cooling procedure. The influence of this loss, however, is very small. Another loss occurs when the spindle oil freezes, but the freezing temperature is beyond the maximum operation temperature. Fig. 1 gives the isobar data on the electrical resistivity p in a temperature range from 4.2 up to 150 K. In the figure, the pressures actually used were in the order 0, 2.4, 4.4, 1 .8, 0 and 4.9 kb. Detailed and magnified information at lower temperatures is plotted in fig. 2, where the pressures quoted from fig. 1 are 0, 2.4 and 4.9 kb. As indicated by arrows in fig. 2, Tc at
Volume 70A, number 5,6
PHYSICS LETTERS
I
I
2 April 1979
8 I
_____
30
P1 kb)
~
I
7
150
/
oo~
°
~
50
/ ~
20
///\~‘
—
P1kb)
4
5
6°
//J-~j.8~
/
I0•
//
Fig. 3. Pressure dependence of T~and TM for CeAg.
/
0
/
,1 I
0
50
I
T (K)
100
150
[2, 3] is satisfactory. (ii) As was expected, the hysteresis phenomenon appears around TM as in fig. 1, when the resistivity measurement was carried out under pressures. But no hysteresis was found, as in fig. 2, at T~. (iii) The measurements were completely reversible in magnitude: the values of Tc, TM and p before and
at various pressures.
after pressure application were the same. This fact may substantiate the circumstance that the applied pressure is hydrostatic and/or the magnetic properties
each pressure was uniquely determined. On the other hand, TM in the present work was defined as the ternperature corresponding to the center of the width of the hysteresis in fig. 1. The clear and important results obtained are summarized as follows. (i) The values of T~and TM at normal pressure were 5.5 and 16 K, respectively, and
of the specimen are reversible in pressure. The variation of T~and TM with pressure is shown in fig. 3, where the data on T~and TM should be read with left-hand and right-hand scales in the ordinate, respectively. The vertical bars in the plot of TM represent the width of the hysteresis in fig. 1. The summarized results are as follows. (i) The variation of T~and TM with pressure is not necessarily linear. Although both
the agreement of these values with the published data
transition temperatures increase with increasing pres-
Fig. 1. The electrical resistivity of CeAg versus temperature
sure, the variation is rather concave downward for T~ I
I
P4.9kb
______
6
1
1
~
in this pressure effect are the same as those in the case of the alloying effect in CeAg~In~~[3]. (i~Frnm
the curves in fig. 3. The results thus obtained are.
C
..‘
and almost linear for TM up to about 4 kb, suggesting a rapid increase at higher pressures. The trends found~
2
P=
z~T~/~p+ 0.4 deg/kb and z~TM/z~p + 20 deg/kb.
0kb
No available data have been found on the pressure 0
—~-~
4
5
6
7
8
9
I0
II
Fig. 2. The electrical resistivity of CeAg versus temperature near Te at various pressures.
effect on Te and TM for CeAg, but the value of L~TMfL~p in the present work agrees very well with the result of ~TM/~p obtained for LaAg [6]. (iii) So far as the temperature range operated is concerned, the resistivity p at a given temperature increases with pres473
Volume 70A number 5,6
PHYSICS LETTERS
2 April 1979
sure. A quantitative evaluation of zip/p, however, should be made with the compressibility data.
In conclusion, the pressure effects on T~and TM in the present work likely reflect the result of the alloy-
In the course of discussing the alloying effect on Tc and TM of CeAg, it has been pointed out [3] that the most important factors are the location of the Fermi energy level relative to the high density of states and the shift of the level associated with the Jahn—Teller distortion. This way of analysis may be applicable to the results of the pressure effects on T~,TM and p which were carried out in the present work. The increase in Tc with pressure suggests an enhancement of the s—f exchange interaction resulting from an upward shift of the Fermi energy level with pressure. The fact that both zXTM/~pand z~TM/1~c, where c is the concentration of substituted element In in the alloy-
ing effect and will be a more direct way to further investigate the electronic structure than the alloying effect. Details will be reported in the near future.
ing effect, are positive may support a situation in which the distortion due to pressure may be in the same direction as that due to the Jahn—Teller distortion.
474
References [11 R.E.
Walline and W.E. Wallace, J. Chem. Phys. 41(1964)
3285. [21 D. Schmitt, P. Morjn and J. Pierre, J. Magn. Magn. Mat. 8 249. 131 (1978) II. lhrig and W. Lohmann, J. Phys. Fl (1977) 1957. [41 A. Hasegawa, B. Bremicker and J. Kübler, Z. Phys. B22
(1975) 231.
151 D.K.
Ray and J. Sivardiere, Solid State Commun. 19
(1976) 1053.
L6l J.S. Schilling, S. Methfessel and State Commun. 24 (1977) 659.
R.N. Shelton, Solid