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Pressure effects on crystal structure, magnetic and transport properties of layered perovskite TbBaCo2O5.5
ARTICLE IN PRESS
Physica B 378–380 (2006) 537–538 www.elsevier.com/locate/physb
Pressure effects on crystal structure, magnetic and transport properties of layered perovskite TbBaCo2 O5:5 A. Podlesnyaka,, S. Streulea, K. Condera,b, E. Pomjakushinaa,b, J. Mesota, A. Mirmelsteinc, P. Schu¨tzendorfd, R. Lengsdorfd, M.M. Abd-Elmeguidd a Laboratory for Neutron Scattering, ETHZ & PSI, CH-5232 Villigen PSI, Switzerland Laboratory for Developments and Methods, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland c Institute for Metal Physics RAS, 620219 Ekaterinburg GSP-170, Russia d II. Physikalisches Institut, Universita¨t zu Ko¨ln, Zu¨lpicherstr. 77, 50937 Ko¨ln, Germany
b
Abstract The complex behavior of the RBaCo2 O5:5 perovskites, which include a metal–insulator (MI) as well as successive magnetic (PM ! FM ! AFM) transitions, is suggested to be related to an interplay between spin, charge and orbital degrees of freedom of the Co3þ ions. We have investigated the effect of pressure on the structural, magnetic and electronic properties of TbBaCo2 O5:5 by means of neutron powder diffraction (p ¼ 1:2 GPa), magnetization (p ¼ 1:2 GPa), and resistivity measurements (p ¼ 2:6 GPa), respectively. Contrary to the results reported on conventional (La,Sr)CoO3 perovskites, we find that the pressure coefficients of the transition temperatures T N , T C , as well as T MI are rather small (o1 K=GPa), suggesting a weak change of the spin states at the MI transition. We further show, that pressure and temperature have different effects on the volumes of the CoO6 octahedron and CoO5 pyramid in the layered double-perovskite. r 2006 Elsevier B.V. All rights reserved. PACS: 75.30.m; 71.27.þa; 62.50.þp Keywords: Cobaltites; Pressure; Phase transition
Pressure can modify the magnetic and transport properties of 3d transition metal oxides either by closing the Mott–Hubbard/charge-transfer gap, or by inducing a spinstate transition [1]. Pressure-induced spin-state as well as metal–insulator (MI) transitions were reported for many 3D perovskites, among others La1x Srx CoO3 , MFeO3 (M ¼ La, Pr, Ca) [2–4]. In the present work, we have investigated the effect of pressure on the magnetic, transport and structural properties of layered doubleperovskite cobalt oxides TbBaCo2 O5:5 . These materials have recently attracted renewed attention due to their extraordinary magnetic and transport properties, in particular after the discovery of giant negative magnetoresistance with resistivity ratios 30% in RBaCo2 O5:4 (R ¼ Eu, Gd) [5]. Surprisingly, we find contrary to Corresponding author. Tel.: +41 56 310 4613; fax: +41 56 310 2939.
E-mail address: [email protected] (A. Podlesnyak). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.405
conventional (La,Sr)CoO3 perovskites [4], that pressure has a weak influence on both magnetic (see Fig. 1) and transport (see Fig. 2) properties. In this short article we only focus on the structural properties. The neutron powder diffraction (NPD) experiments were carried out using a zero-matrix clamp pressure cell made of Zi/Ti alloy. The data were collected on the HRPT highresolution diffractometer at the spallation source SINQ, Switzerland, using a wavelength of l ¼ 1:494 A˚. The program FullProf was applied for the refinement [6]. The measurements of the magnetic susceptibility were carried out in a Quantum Design PPMS system. For the experiments under pressure a clamp cell made of nonmagnetic Cu/Be alloy was used, allowing to reach pressures up to 1.5 GPa. The TbBaCo2 O5:5 perovskite consists in consecutive ordered layers of CoO2 –BaO–CoO2 –RO0:5 (see inset of Fig. 2). Selected structural parameters are displayed in
ARTICLE IN PRESS A. Podlesnyak et al. / Physica B 378–380 (2006) 537–538
538
Table 1 Refined structural parameters for TbBaCo2 O5:5
0.06 0.05 dM/dT
Magnetization (a.u.)
0.008
0.04
0.004
Tc = 280 K
0.000 TN = 252 K
0.03
-0.004 200
0.02
220
240 260 Temperature (K)
280
0.01 0.00
0
50
100
150
200
250
300
Temperature (K) Fig. 1. (Color online) Temperature dependence of the ZFC magnetization of TbBaCo2 O5:5 . Circles and boxes denote measurements at zero pressure and p ¼ 1:2 GPa, respectively. Inset shows dM=dT.
Temperature (K) Pressure (GPa)
260 0
260 1.2
100 0
a (A˚) b (A˚) c (A˚) ˚3 V ðA˚ ) Tb (2p) (1/2 y 1/2) Ba (2o) (1/2 y 0) Co1 (2r) (0 1/2 z) Co2 (2q) (0 0 z) O4 (2s) (1/2 0 z) O5 (2t) (1/2 1/2 z) O6 (4u) (0 y z); y z V octa (A˚3 ) V pyr (A˚3 )
3.8691(1) 7.8021(1) 7.5244(1) 227.140
3.8614(1) 7.7765(3) 7.5086(3) 225.470
3.8680(1) 7.7899(1) 7.5130(1) 226.377
0.2690(5) 0.2470(5) 0.2545(9) 0.2587(9) 0.3148(6) 0.2751(7) 0.2392(5) 0.2902(5) 9.87(1) 5.70(1)
0.2674(9) 0.2520(15) 0.2565(38) 0.2530(44) 0.3064(11) 0.2791(12) 0.2436(9) 0.2921(9) 9.64(1) 5.61(1)
0.2703(5) 0.2465(5) 0.2567(9) 0.2585(9) 0.3157(6) 0.2782(7) 0.2380(5) 0.2899(5) 9.89(1) 5.67(1)
Wyckoff positions of the O(1)–O(3) ions are 1a, (0 0 0) for O(1); 1e, (0 1/ 2 0) for O(2); 1g, (0 1/2 1/2) for O(3).
10
Tb
1
O(3) O(4)
R (T) [Ω]
O(6)
O(5)
Co(2)
Co(1)
Ba O(1)
O(2)
0.1
2.61 GPa
1.65 GPa
0.01
2.06 GPa
200
240
280
320
360
400
440
480
T [K] Fig. 2. (Color online) Temperature dependence of the resistivity rðp; TÞ of TbBaCo2 O5:5 . Measurements were performed in a diamond anvil cell. Inset shows a polyhedral view of the layered double-perovskite.
Table 1. The detailed analysis of the observed structural variation with temperature as well as under pressure will be published elsewhere [7]. Currently, based on a comparison of the experimentally determined values for Co–O bond lengths, we conclude that pressure and temperature have different effects on the octahedron and pyramid volumes (V oct and V pyr ). As expected, the unit-cell parameters, and hence unit-cell volume, contract under pressure as well as on temperature decrease (see Table 1). Both V oct and V pyr
shrink on applying a pressure of p ¼ 1:2 GPa. In contrast to this, V oct slightly increases when the temperature is lowered from 260 to 100 K. This volume expansion could be an evidence for a transition of octahedral Co3þ ions to a higher spin state, since the effective volume of the CoO6 octahedron is 9.51 and 10.83 A˚ for LS and HS state, respectively [8]. Note that the pyramid volumes shrink as expected. The authors are grateful to V. Pomjakushin for his help with NPD measurements and Yu. Chernenkov for stimulating discussions. The experiments have been partly performed at the Swiss Spallation Neutron Source, Paul Scherrer Institute, Villigen, Switzerland. The work was supported by Swiss National Science Foundation through Grants 200021–100194, SCOPES IB7320-110859/1, NCCR MaNEP project, and the Deutsche Forschungsgemeinschaft through SFB 608. References [1] [2] [3] [4] [5] [6] [7]
V. Ksenofonov, et al., Top. Curr. Chem. 235 (2004) 23. M. Pasternak, et al., Phys. Rev. Lett. 79 (1997) 5046. T. Vogt, et al., Phys. Rev. B 67 (2003) 140401. R. Lengsdorf, et al., Phys. Rev. B 69 (2004) 140403. C. Martin, et al., Appl. Phys. Lett. 71 (1997) 1421. J. Rodriguez-Carvajal, Physica B 192 (1993) 55. A. Podlesnyak, et al., NovaScience Publishers, Inc. N.Y. 2005, to be published. [8] R.D. Shennon, Acta Cryst. A 32 (1976) 751.
Physica B 378–380 (2006) 537–538 www.elsevier.com/locate/physb
Pressure effects on crystal structure, magnetic and transport properties of layered perovskite TbBaCo2 O5:5 A. Podlesnyaka,, S. Streulea, K. Condera,b, E. Pomjakushinaa,b, J. Mesota, A. Mirmelsteinc, P. Schu¨tzendorfd, R. Lengsdorfd, M.M. Abd-Elmeguidd a Laboratory for Neutron Scattering, ETHZ & PSI, CH-5232 Villigen PSI, Switzerland Laboratory for Developments and Methods, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland c Institute for Metal Physics RAS, 620219 Ekaterinburg GSP-170, Russia d II. Physikalisches Institut, Universita¨t zu Ko¨ln, Zu¨lpicherstr. 77, 50937 Ko¨ln, Germany
b
Abstract The complex behavior of the RBaCo2 O5:5 perovskites, which include a metal–insulator (MI) as well as successive magnetic (PM ! FM ! AFM) transitions, is suggested to be related to an interplay between spin, charge and orbital degrees of freedom of the Co3þ ions. We have investigated the effect of pressure on the structural, magnetic and electronic properties of TbBaCo2 O5:5 by means of neutron powder diffraction (p ¼ 1:2 GPa), magnetization (p ¼ 1:2 GPa), and resistivity measurements (p ¼ 2:6 GPa), respectively. Contrary to the results reported on conventional (La,Sr)CoO3 perovskites, we find that the pressure coefficients of the transition temperatures T N , T C , as well as T MI are rather small (o1 K=GPa), suggesting a weak change of the spin states at the MI transition. We further show, that pressure and temperature have different effects on the volumes of the CoO6 octahedron and CoO5 pyramid in the layered double-perovskite. r 2006 Elsevier B.V. All rights reserved. PACS: 75.30.m; 71.27.þa; 62.50.þp Keywords: Cobaltites; Pressure; Phase transition
Pressure can modify the magnetic and transport properties of 3d transition metal oxides either by closing the Mott–Hubbard/charge-transfer gap, or by inducing a spinstate transition [1]. Pressure-induced spin-state as well as metal–insulator (MI) transitions were reported for many 3D perovskites, among others La1x Srx CoO3 , MFeO3 (M ¼ La, Pr, Ca) [2–4]. In the present work, we have investigated the effect of pressure on the magnetic, transport and structural properties of layered doubleperovskite cobalt oxides TbBaCo2 O5:5 . These materials have recently attracted renewed attention due to their extraordinary magnetic and transport properties, in particular after the discovery of giant negative magnetoresistance with resistivity ratios 30% in RBaCo2 O5:4 (R ¼ Eu, Gd) [5]. Surprisingly, we find contrary to Corresponding author. Tel.: +41 56 310 4613; fax: +41 56 310 2939.
E-mail address: [email protected] (A. Podlesnyak). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.405
conventional (La,Sr)CoO3 perovskites [4], that pressure has a weak influence on both magnetic (see Fig. 1) and transport (see Fig. 2) properties. In this short article we only focus on the structural properties. The neutron powder diffraction (NPD) experiments were carried out using a zero-matrix clamp pressure cell made of Zi/Ti alloy. The data were collected on the HRPT highresolution diffractometer at the spallation source SINQ, Switzerland, using a wavelength of l ¼ 1:494 A˚. The program FullProf was applied for the refinement [6]. The measurements of the magnetic susceptibility were carried out in a Quantum Design PPMS system. For the experiments under pressure a clamp cell made of nonmagnetic Cu/Be alloy was used, allowing to reach pressures up to 1.5 GPa. The TbBaCo2 O5:5 perovskite consists in consecutive ordered layers of CoO2 –BaO–CoO2 –RO0:5 (see inset of Fig. 2). Selected structural parameters are displayed in
ARTICLE IN PRESS A. Podlesnyak et al. / Physica B 378–380 (2006) 537–538
538
Table 1 Refined structural parameters for TbBaCo2 O5:5
0.06 0.05 dM/dT
Magnetization (a.u.)
0.008
0.04
0.004
Tc = 280 K
0.000 TN = 252 K
0.03
-0.004 200
0.02
220
240 260 Temperature (K)
280
0.01 0.00
0
50
100
150
200
250
300
Temperature (K) Fig. 1. (Color online) Temperature dependence of the ZFC magnetization of TbBaCo2 O5:5 . Circles and boxes denote measurements at zero pressure and p ¼ 1:2 GPa, respectively. Inset shows dM=dT.
Temperature (K) Pressure (GPa)
260 0
260 1.2
100 0
a (A˚) b (A˚) c (A˚) ˚3 V ðA˚ ) Tb (2p) (1/2 y 1/2) Ba (2o) (1/2 y 0) Co1 (2r) (0 1/2 z) Co2 (2q) (0 0 z) O4 (2s) (1/2 0 z) O5 (2t) (1/2 1/2 z) O6 (4u) (0 y z); y z V octa (A˚3 ) V pyr (A˚3 )
3.8691(1) 7.8021(1) 7.5244(1) 227.140
3.8614(1) 7.7765(3) 7.5086(3) 225.470
3.8680(1) 7.7899(1) 7.5130(1) 226.377
0.2690(5) 0.2470(5) 0.2545(9) 0.2587(9) 0.3148(6) 0.2751(7) 0.2392(5) 0.2902(5) 9.87(1) 5.70(1)
0.2674(9) 0.2520(15) 0.2565(38) 0.2530(44) 0.3064(11) 0.2791(12) 0.2436(9) 0.2921(9) 9.64(1) 5.61(1)
0.2703(5) 0.2465(5) 0.2567(9) 0.2585(9) 0.3157(6) 0.2782(7) 0.2380(5) 0.2899(5) 9.89(1) 5.67(1)
Wyckoff positions of the O(1)–O(3) ions are 1a, (0 0 0) for O(1); 1e, (0 1/ 2 0) for O(2); 1g, (0 1/2 1/2) for O(3).
10
Tb
1
O(3) O(4)
R (T) [Ω]
O(6)
O(5)
Co(2)
Co(1)
Ba O(1)
O(2)
0.1
2.61 GPa
1.65 GPa
0.01
2.06 GPa
200
240
280
320
360
400
440
480
T [K] Fig. 2. (Color online) Temperature dependence of the resistivity rðp; TÞ of TbBaCo2 O5:5 . Measurements were performed in a diamond anvil cell. Inset shows a polyhedral view of the layered double-perovskite.
Table 1. The detailed analysis of the observed structural variation with temperature as well as under pressure will be published elsewhere [7]. Currently, based on a comparison of the experimentally determined values for Co–O bond lengths, we conclude that pressure and temperature have different effects on the octahedron and pyramid volumes (V oct and V pyr ). As expected, the unit-cell parameters, and hence unit-cell volume, contract under pressure as well as on temperature decrease (see Table 1). Both V oct and V pyr
shrink on applying a pressure of p ¼ 1:2 GPa. In contrast to this, V oct slightly increases when the temperature is lowered from 260 to 100 K. This volume expansion could be an evidence for a transition of octahedral Co3þ ions to a higher spin state, since the effective volume of the CoO6 octahedron is 9.51 and 10.83 A˚ for LS and HS state, respectively [8]. Note that the pyramid volumes shrink as expected. The authors are grateful to V. Pomjakushin for his help with NPD measurements and Yu. Chernenkov for stimulating discussions. The experiments have been partly performed at the Swiss Spallation Neutron Source, Paul Scherrer Institute, Villigen, Switzerland. The work was supported by Swiss National Science Foundation through Grants 200021–100194, SCOPES IB7320-110859/1, NCCR MaNEP project, and the Deutsche Forschungsgemeinschaft through SFB 608. References [1] [2] [3] [4] [5] [6] [7]
V. Ksenofonov, et al., Top. Curr. Chem. 235 (2004) 23. M. Pasternak, et al., Phys. Rev. Lett. 79 (1997) 5046. T. Vogt, et al., Phys. Rev. B 67 (2003) 140401. R. Lengsdorf, et al., Phys. Rev. B 69 (2004) 140403. C. Martin, et al., Appl. Phys. Lett. 71 (1997) 1421. J. Rodriguez-Carvajal, Physica B 192 (1993) 55. A. Podlesnyak, et al., NovaScience Publishers, Inc. N.Y. 2005, to be published. [8] R.D. Shennon, Acta Cryst. A 32 (1976) 751.