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High-pressure resistivity of Ce(Ru0.85Rh0.15)2Si2
Physica B 259—261 (1999) 63—65
High-pressure resistivity of Ce(Ru Rh ) Si C. Sekine *, K. Kiho , I. Shirotani , S. Murayama , G. Oomi, Y. O nuki Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan Department of Mechanical Engineering and Materials Science, Kumamoto University, Kumamoto 860, Japan Department of Physics, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan
Abstract Ce(Ru Rh ) Si is the itinerant antiferromagnetic heavy-fermion compound (Ne´el temperature ¹ "5.5 K). The , temperature dependence of electrical resistivity parallel and perpendicular to the tetragonal c-axis on a single-crystalline sample of this compound has been measured under hydrostatic pressure up to 2 GPa. It is found that ¹ is depressed , with pressure at the rate of (d¹ /dP) "!3.9 K/GPa. Such a strong dependence on pressure is seen as a consequence , . of the delicate Fermi-surface nesting that results in a spin-density-wave transition. 1999 Elsevier Science B.V. All rights reserved. Keywords: SDW; Ce(Ru Rh ) Si ; High pressure
The pseudo-ternary compounds Ce(Ru Rh ) Si \V V with the ThCr Si -type tetragonal structure show a very rich electronic and magnetic phase diagram as a function of the concentration x, the magnetic field B and the applied pressure P. This system exhibits a variety of behaviors, including heavy-fermion character, metamagnetic transition [1], non-Fermi liquid behavior [2,3], local-moment magnetic ordering for x'0.5 [4] and superconductivity for x"1 at high pressure [5]. Furthermore, a weak antiferromagnetic (AF) phase exists in the Ru rich region (0.05(x(0.3) [6]. The ordering temperature ¹ has a maximum at x"0.15 (¹ " , , 5.5 K). A neutron diffraction experiment for x"0.15 shows that the AF phase has an incommensurate sinusoidal spin modulation with a wave vector q"(0, 0, 0.42) and that the magnetic moment is polarized along the c-axis with the amplitude of 0.65 l /Ce [4]. Recent resistivity measurements on Ce(Ru Rh ) Si have suggested that a partial gapping of the Fermi surface occurs associated with the development of a spin-
* Corresponding author. Tel.: #81-143-46-5551; fax: #81143-46-5501; e-mail: [email protected].
density-wave (SDW) [7]. Hydrostatic pressure has been an important tool for investigating the SDW transition in Cr [8]. In the present work we have measured the electrical resistivity of Ce(Ru Rh ) Si under high pres sure to elucidate the character of the ordered state of this compound. High-quality single-crystalline sample of Ce(Ru Rh ) Si was grown by the Czochralski technique in a tri-arc furnace. Resistivity was measured with a standard DC four-probe method in the range of 2—300 K. The hydrostatic pressure was generated by using a WC piston and a CuBe cylinder device operating up to 2 GPa. A mixture of Fluorinert, FC70 and FC77 was used as the pressure-transmitting medium. The load is always kept constant by controlling the oil pressure of the hydraulic press. Pressure inside the cell was calibrated by the phase transition of NH F at room temperature. The temperature was measured with a thermocouple put in the cell. The detail of the apparatus was reported previously [9]. Fig. 1a and b shows the results of the resistivity measurements for small slices cleaved to directions parallel (o ) and perpendicular (o ) to the tetragonal c-axis , , with excitation current, respectively, at various hydrostatic pressures up to 2 GPa. As shown in this figure, the
0921-4526/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 7 2 1 - 2
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C. Sekine et al. / Physica B 259—261 (1999) 63—65
Fig. 2. Resistivity of Ce(Ru Rh ) Si in the parallel direc tion at low-temperature region under hydrostatic pressure. Inset: transition temperature ¹ versus applied hydrostatic , pressure.
Fig. 1. Temperature dependence of the electrical resistivity of Ce(Ru Rh ) Si for the current in the basal plane (a) or parallel to the c-axis (b) at various pressures.
temperature dependence of each resistivity is strongly anisotropic. At ambient pressure, o decreases gradually , with temperature (down to 50 K). A shoulder is observed around 20 K, which is also the effective Kondo temperature ¹ derived from specific heat experiments ) [6]. This shoulder is much more pronounced and becomes a maximum for o . The temperature of resistiv, ity maximum (o ) or shoulder (o ) is found to increase , , with increasing pressure and both the anomalies tend to be smeared at high pressure. These results indicate the enhancement of ¹ under high pressure. Similar behav) ior was observed on CeRu Si in hydrostatic pressure [10]. Fig. 2 shows the effect of hydrostatic pressure on o of , Ce(Ru Rh ) Si in the low-temperature region. The kink (¹ ) observed at 5.5 K for ambient pressure is in , good agreement with the value in a preceding paper [7]. This anomaly is visible only in the parallel direction (o ). , On the other hand, o shows a rather continuous de, crease with decreasing temperature. Application of a rather small pressure, between 0.4 and 0.6 GPa, suppresses any resistive signature for the low-temperature phase transition. The inset in Fig. 2 shows ¹ versus , applied hydrostatic pressure, obtained from the kinks in o . The transition temperature ¹ is depressed linearly , , with pressure. A solid line passes through the data points, with a slope (d¹ /dP) "!3.9 K/GPa. Such a , . strong dependence on pressure is consistent with the transition in Ce(Ru Rh ) Si being due to a Fermi surface instability (SDW).
Following an earlier analysis of the conductivity of Cr [8] and Ce(Ru Rh ) Si [7], the total conductivity is written as p"p #p if one assumes that the Fermi surface is divided into two independent parts, where indices 1 and 2 refer to the ungapped and gapped magnetic regions of the Fermi-surface at zero pressure and magnetic field, respectively. Then, the relative change in conductivity produced by SDW is given by
p !p o !o p p " " 1! . (1) p o p p Here, the subscripts g and p refer to the case when the magnetic region 2 is gapped or made paramagnetic by application of pressure, respectively. Then, we estimate ratio (1) experimentally. We assume that the paramagnetic background (o ) that has to be subtracted, is given by the P"0.6 GPa curve of Fig. 2. Correcting a temperature-independent resistivity shift by pressure as a background effect, we can roughly estimate zero-temperature value of ratio (1) in zero pressure as &0.45 taking the extrapolation of ¹P0 K. The p /p can be calculated by using the formula given by a SDW gap D and ¹ [8]. , For ¹P0 K the contribution of the gapped magnetic part p /p is zero in any case. Therefore, we obtain (p !p )/p "p /p "0.45 for zero pressure. The ratio p /p is related to the percentage of the Fermi-surface that is gapped along the c-axis. The value is in good agreement with 0.5, which is obtained by analysis of magnetoresistivity [7].
References [1] P. Haen, J. Flouquet, F. Lapierre, P. Lejay, G. Remenyi, J. Low Temp. Phys. 67 (1987) 391. [2] T. Taniguchi, Y. Tabata, H. Tanabe, Y. Miyako, Physica B 230—232 (1997) 123.
C. Sekine et al. / Physica B 259—261 (1999) 63—65 [3] T. Graf, J.D. Thompson, M.F. Hundley, R. Movshovich, Z. Fisk, D. Mandrus, R.A. Fisher, N.E. Phillips, Phys. Rev. Lett. 78 (1997) 3769. [4] S. Kawarazaki, Y. Kobashi, J.A. Fernandez-Baca, S. Murayama, Y. Onuki, Y. Miyako, Physica B 206 & 207 (1995) 298. [5] R. Movshovich, T. Graf, D. Mandrus, J.D. Thompson, J.L. Smith, Z. Fisk, Phys. Rev. B 53 (1996) 8241. [6] C. Sekine, T. Sakakibara, H. Amitsuka, Y. Miyako, T. Goto, J. Phys. Soc. Japan 61 (1992) 4536.
65
[7] S. Murayama, C. Sekine, A. Yokoyanagi, K. Hoshi, Y. Onuki, Phys. Rev. B 56 (1997) 11092. [8] D.B. McWhan, T.M. Rice, Phys. Rev. Lett. 19 (1967) 846. [9] C. Sekine, T. Shimizu, I. Shirotani, G. Oomi, Memoirs of the Muroran Institute of Technology 47 (1997) 73. [10] J.M. Mignot, A. Ponchet, P. Haen, F. Lapierre, J. Flouquet, Phys. Rev. B 40 (1990) 10917.
High-pressure resistivity of Ce(Ru Rh ) Si C. Sekine *, K. Kiho , I. Shirotani , S. Murayama , G. Oomi, Y. O nuki Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan Department of Mechanical Engineering and Materials Science, Kumamoto University, Kumamoto 860, Japan Department of Physics, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan
Abstract Ce(Ru Rh ) Si is the itinerant antiferromagnetic heavy-fermion compound (Ne´el temperature ¹ "5.5 K). The , temperature dependence of electrical resistivity parallel and perpendicular to the tetragonal c-axis on a single-crystalline sample of this compound has been measured under hydrostatic pressure up to 2 GPa. It is found that ¹ is depressed , with pressure at the rate of (d¹ /dP) "!3.9 K/GPa. Such a strong dependence on pressure is seen as a consequence , . of the delicate Fermi-surface nesting that results in a spin-density-wave transition. 1999 Elsevier Science B.V. All rights reserved. Keywords: SDW; Ce(Ru Rh ) Si ; High pressure
The pseudo-ternary compounds Ce(Ru Rh ) Si \V V with the ThCr Si -type tetragonal structure show a very rich electronic and magnetic phase diagram as a function of the concentration x, the magnetic field B and the applied pressure P. This system exhibits a variety of behaviors, including heavy-fermion character, metamagnetic transition [1], non-Fermi liquid behavior [2,3], local-moment magnetic ordering for x'0.5 [4] and superconductivity for x"1 at high pressure [5]. Furthermore, a weak antiferromagnetic (AF) phase exists in the Ru rich region (0.05(x(0.3) [6]. The ordering temperature ¹ has a maximum at x"0.15 (¹ " , , 5.5 K). A neutron diffraction experiment for x"0.15 shows that the AF phase has an incommensurate sinusoidal spin modulation with a wave vector q"(0, 0, 0.42) and that the magnetic moment is polarized along the c-axis with the amplitude of 0.65 l /Ce [4]. Recent resistivity measurements on Ce(Ru Rh ) Si have suggested that a partial gapping of the Fermi surface occurs associated with the development of a spin-
* Corresponding author. Tel.: #81-143-46-5551; fax: #81143-46-5501; e-mail: [email protected].
density-wave (SDW) [7]. Hydrostatic pressure has been an important tool for investigating the SDW transition in Cr [8]. In the present work we have measured the electrical resistivity of Ce(Ru Rh ) Si under high pres sure to elucidate the character of the ordered state of this compound. High-quality single-crystalline sample of Ce(Ru Rh ) Si was grown by the Czochralski technique in a tri-arc furnace. Resistivity was measured with a standard DC four-probe method in the range of 2—300 K. The hydrostatic pressure was generated by using a WC piston and a CuBe cylinder device operating up to 2 GPa. A mixture of Fluorinert, FC70 and FC77 was used as the pressure-transmitting medium. The load is always kept constant by controlling the oil pressure of the hydraulic press. Pressure inside the cell was calibrated by the phase transition of NH F at room temperature. The temperature was measured with a thermocouple put in the cell. The detail of the apparatus was reported previously [9]. Fig. 1a and b shows the results of the resistivity measurements for small slices cleaved to directions parallel (o ) and perpendicular (o ) to the tetragonal c-axis , , with excitation current, respectively, at various hydrostatic pressures up to 2 GPa. As shown in this figure, the
0921-4526/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 7 2 1 - 2
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C. Sekine et al. / Physica B 259—261 (1999) 63—65
Fig. 2. Resistivity of Ce(Ru Rh ) Si in the parallel direc tion at low-temperature region under hydrostatic pressure. Inset: transition temperature ¹ versus applied hydrostatic , pressure.
Fig. 1. Temperature dependence of the electrical resistivity of Ce(Ru Rh ) Si for the current in the basal plane (a) or parallel to the c-axis (b) at various pressures.
temperature dependence of each resistivity is strongly anisotropic. At ambient pressure, o decreases gradually , with temperature (down to 50 K). A shoulder is observed around 20 K, which is also the effective Kondo temperature ¹ derived from specific heat experiments ) [6]. This shoulder is much more pronounced and becomes a maximum for o . The temperature of resistiv, ity maximum (o ) or shoulder (o ) is found to increase , , with increasing pressure and both the anomalies tend to be smeared at high pressure. These results indicate the enhancement of ¹ under high pressure. Similar behav) ior was observed on CeRu Si in hydrostatic pressure [10]. Fig. 2 shows the effect of hydrostatic pressure on o of , Ce(Ru Rh ) Si in the low-temperature region. The kink (¹ ) observed at 5.5 K for ambient pressure is in , good agreement with the value in a preceding paper [7]. This anomaly is visible only in the parallel direction (o ). , On the other hand, o shows a rather continuous de, crease with decreasing temperature. Application of a rather small pressure, between 0.4 and 0.6 GPa, suppresses any resistive signature for the low-temperature phase transition. The inset in Fig. 2 shows ¹ versus , applied hydrostatic pressure, obtained from the kinks in o . The transition temperature ¹ is depressed linearly , , with pressure. A solid line passes through the data points, with a slope (d¹ /dP) "!3.9 K/GPa. Such a , . strong dependence on pressure is consistent with the transition in Ce(Ru Rh ) Si being due to a Fermi surface instability (SDW).
Following an earlier analysis of the conductivity of Cr [8] and Ce(Ru Rh ) Si [7], the total conductivity is written as p"p #p if one assumes that the Fermi surface is divided into two independent parts, where indices 1 and 2 refer to the ungapped and gapped magnetic regions of the Fermi-surface at zero pressure and magnetic field, respectively. Then, the relative change in conductivity produced by SDW is given by
p !p o !o p p " " 1! . (1) p o p p Here, the subscripts g and p refer to the case when the magnetic region 2 is gapped or made paramagnetic by application of pressure, respectively. Then, we estimate ratio (1) experimentally. We assume that the paramagnetic background (o ) that has to be subtracted, is given by the P"0.6 GPa curve of Fig. 2. Correcting a temperature-independent resistivity shift by pressure as a background effect, we can roughly estimate zero-temperature value of ratio (1) in zero pressure as &0.45 taking the extrapolation of ¹P0 K. The p /p can be calculated by using the formula given by a SDW gap D and ¹ [8]. , For ¹P0 K the contribution of the gapped magnetic part p /p is zero in any case. Therefore, we obtain (p !p )/p "p /p "0.45 for zero pressure. The ratio p /p is related to the percentage of the Fermi-surface that is gapped along the c-axis. The value is in good agreement with 0.5, which is obtained by analysis of magnetoresistivity [7].
References [1] P. Haen, J. Flouquet, F. Lapierre, P. Lejay, G. Remenyi, J. Low Temp. Phys. 67 (1987) 391. [2] T. Taniguchi, Y. Tabata, H. Tanabe, Y. Miyako, Physica B 230—232 (1997) 123.
C. Sekine et al. / Physica B 259—261 (1999) 63—65 [3] T. Graf, J.D. Thompson, M.F. Hundley, R. Movshovich, Z. Fisk, D. Mandrus, R.A. Fisher, N.E. Phillips, Phys. Rev. Lett. 78 (1997) 3769. [4] S. Kawarazaki, Y. Kobashi, J.A. Fernandez-Baca, S. Murayama, Y. Onuki, Y. Miyako, Physica B 206 & 207 (1995) 298. [5] R. Movshovich, T. Graf, D. Mandrus, J.D. Thompson, J.L. Smith, Z. Fisk, Phys. Rev. B 53 (1996) 8241. [6] C. Sekine, T. Sakakibara, H. Amitsuka, Y. Miyako, T. Goto, J. Phys. Soc. Japan 61 (1992) 4536.
65
[7] S. Murayama, C. Sekine, A. Yokoyanagi, K. Hoshi, Y. Onuki, Phys. Rev. B 56 (1997) 11092. [8] D.B. McWhan, T.M. Rice, Phys. Rev. Lett. 19 (1967) 846. [9] C. Sekine, T. Shimizu, I. Shirotani, G. Oomi, Memoirs of the Muroran Institute of Technology 47 (1997) 73. [10] J.M. Mignot, A. Ponchet, P. Haen, F. Lapierre, J. Flouquet, Phys. Rev. B 40 (1990) 10917.