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Cr-doping effect on the perovskite (Nd, Sr) MnO3 single crystals
Physica B 312–313 (2002) 754–756
Cr-doping effect on the perovskite (Nd, Sr) MnO3 single crystals Jun Takeuchi*, Seitaro Hirahara, Tara P. Dhakal, Kiyotaka Miyoshi, Kenji Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The effect of Cr-doping on the Mn site in Nd1ySryMnO3 (y ¼ 0:5 and 0.55) single crystals grown by the floating zone method has been studied. The y ¼ 0:5 mother material exhibits a transition at TC ¼ 260 K to be a ferromagnetic metal (FMM) and at TN ¼ 160 K to be an antiferromagnetic insulator (AFMI). The doping of 5 at% Cr3+ ions lowers TC to be 250 K and completely suppresses the AFMI. The y ¼ 0:55 mother material exhibits a transition at TN ¼ 230 K to be an antiferromagnetic metal . The doping of 5 at% Cr3+ ions changes the state to be similar to y ¼ 0:5 mother material having the FMM and AFMI. The doping of 10 at% Cr3+ ions completely suppresses the AFMI and keeps the FMM. In both cases, small amount of Cr-doping stabilizes the FMM, which is probably caused by provoking the double exchange interaction between Mn3+/Mn4+ pairs. r 2002 Elsevier Science B.V. All rights reserved. PACS: 71.30.th; 75.30.Hx; 75.30.Vn Keywords: Metal–insulator transition; Doping effects; Colossal magnetoresistance; Charge ordering
There has been renewed interest in physical properties of hole-doped perovskite manganites Ln1xAxMnO3, since these materials show exotic electronic transport and magnetic properties [1]. Double exchange (DE) interactions between Mn3+/Mn4+ pairs and the lattice distortion are believed to play an important role for the properties of these materials. Though many works have been done through doping of the Ln sites, far fewer studies have been made in doping Mn sites, which are at the heart of the DE [2,3]. Recently, it has been revealed that a small amount of Cr-doping on the Mn site in Ln0.5Ca0.5MnO3 has a strong influence on the magnetic and electronic properties [4–7]. In this work, we have undertaken a study of the effect of Cr-doping in Nd1ySryMn1xCrxO3 single crystals with y ¼ 0:5 and 0.55 grown by the floating-zone method having been *Corresponding author. Tel.: +81-852-32-6390; fax: +81852-32-6409. E-mail address: [email protected] (J. Takeuchi).
useful for doped single crystals Nd0.67Sr0.33Mn1xMxO3 (M=Fe, Co) [8,9]. The temperature dependence of the magnetization measured by the SQUID magnetometer for Nd1ySryMn1xCrxO3 at a field of 0.1 T is shown in Fig. 1. The mother material for y ¼ 0:5 system shows a ferromagnetic transition at TC ¼ 260 K and then an antiferromagnetic transition at TN ¼ 160 K accompanied with abrupt increase and decrease of the magnetization as lowering temperatures. The doping of 5 at% Cr3+ ions lowers TC to be 250 K, and keeps the ferromagnetic state to the lowest temperature (10 K) measured suppressing completely the antiferromagnetic state. The mother material for y ¼ 0:55 system shows an antiferromagnetic transition at TN ¼ 230 K, where a small peak appears in the magnetization. The doping of 5 at% Cr3+ ions changes the magnetic state to be similar to y ¼ 0:5 mother material having TC ¼ 250 K and TN ¼ 140 K. The doping of 10 at% Cr3+ ions raises TC to be 260 K, and keeps the ferromagnetic state to the lowest temperature measured.
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 2 2 - 4
J. Takeuchi et al. / Physica B 312–313 (2002) 754–756
(a) y =0.5
Nd1-ySryMn1-xCrxO3
1
x=0.05 H=0.1T
M [µ B/f.u.]
0.5
Open Symbols: ZFC Closed Symbols: FC
x=0
0
(b)y=0.55 x=0.1
1
x=0.05
0.5 0
x=0
0
100
200
T [K]
300
Fig. 1. Temperature dependence of the magnetization for Nd1ySryMn1xCrxO3 at a field of 0.1 T.
104 102
ρ [ Ω · cm]
10
(a) y=0.5
Nd1-ySryMn1-xCrxO3
Closed Symbols: 0T Open Symbols: 7T
0
10-1 10-2
x=0
10-3
x=0.05
10-2
(b) y=0.55
x=0.05
10-1
10-2
10-2
x=0
10-3
10-3
x=0.1
10-4
10-4
0
100
T [K]
Fig. 2. Temperature dependence Nd1ySryMn1xCrxO3.
200 of
the
keeping the FMM state in accordance with the magnetization data. It should be noted that the colossal magnetoresistance (CMR) near TC for Cr-doped material is bigger than undoped mother material. The resistivity for y ¼ 0:55 mother material shows metallic behavior below TN ; indicating that this material is antiferromagnetic metal (AFMM), though the resistivity increases slowly at lower temperatures. The resistivity for 5 at% Cr-doped material shows similar behavior to y ¼ 0:5 mother material with FMM and AFMI state. The resistivity for 10 at% Cr-doped material shows metallic conduction below TC keeping the FMM state. The temperature dependence of the linear thermal expansion (LTE) measured by the strain gauge method for Nd1ySryMn1xCrxO3 is shown in Fig. 3. The LTE for y ¼ 0:5 mother material changes drastically at TN probably due to the drastic change in lattice parameters which should be related with the appearance of the spin-, charge- and orbital-ordered state below TN : The temperature where the drastic change of LTE appears is lowered by 60 K under the 7 T magnetic field similar to the temperature dependence of the resistivity behavior. The doping of 5 at% Cr3+ ions completely removes the drastic change of LTE and makes clearer an anomaly near TC : This anomaly is suppressed by the 7 T magnetic field. The LTE for y ¼ 0:55 system also shows gradual decrease below TC and abrupt reduction below TN : These experimental results indicate that Cr3+ ions doped at Mn3+ site has an effect of breaking the spin, charge and orbital ordering in the AFMI state formed by the arrangement of Mn3+ and Mn4+ ions. This is probably due to the stability of Cr3+ ions and isoelectricity of Cr3+ with Mn4+. In this situation, DE interaction between Mn3+/Mn4+ pairs should become effective, which will stabilize the FMM state.
10-5 300 resistivity
755
Nd1-ySryMn1-xCrxO3
for
0.001
(a) y=0.5
x=0 x =0.05
∆ L/ L
The temperature dependence of the resistivity for Nd1ySryMn1xCrxO3 is shown in Fig. 2. The resistivity for y ¼ 0:5 mother material shows metallic behavior below Tc and abrupt increase below TN indicating that this material changes from ferromagnetic metal (FMM) to antiferromagnetic insulator (AFMI) through TN : This AFMI state is believed to be spin-, charge- and orbital-ordered state [10]. The applied magnetic field of 7 T lowers TN by 60 K, which consequently leads that the resistivity at 125 K becomes small by 5 orders of magnitude under 7 T field. The resistivity for 5 at% Cr-doped material shows metallic conduction below TC
Closed Symbols: 0T Open Symbols: 7T
(b) y =0.55 0.001
x =0.05 x=0 x=0.1
0
100
T [K]
200
300
Fig. 3. Temperature dependence of the linear thermal expansion for Nd1ySryMn1xCrxO3.
756
J. Takeuchi et al. / Physica B 312–313 (2002) 754–756
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, World Scientific, Singapore, 1998. [2] K.H. Ahn, X.W. Wu, K. Liu, C.L. Chien, Phys. Rev. B 54 (1996) 15299. [3] N. Gayathri, A.K. Raychaudhuri, S.K. Tiwary, R. Gundakaram, A. Arulraj, C.N.R. Rao, Phys. Rev. B 56 (1997) 1345. [4] B. Raveau, A. Maignan, C. Martin, J. Solid State Chem. 130 (1997) 162.
[5] F. Damay, C. Martin, A. Maignan, M. Hervieu, B. Raveau, F. Bouree, G. Andre, Appl. Phys. Lett. 73 (1998) 3772. [6] T. Kimura, Y. Tomioka, R. Kumai, Y. Okimoto, Y. Tokura, Phys. Rev. Lett. 83 (1999) 3940. [7] Y. Moritomo, A. Machida, S. Mori, N. Yamamoto, A. Nakamura, Phys. Rev. B 60 (1999) 9220. [8] J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, J. Magn. Magn. Mater. 226–230 (2001) 884. [9] T.P. Dhakal, K. Miyoshi, K. Fujiwara, J. Takeuchi, J. Magn. Magn. Mater. 226–230 (2001) 824. [10] H. Kuwahara, Y. Tomioka, A. Asamitsu, Y. Moritomo, Y. Tokura, Science 270 (1995) 961.
Cr-doping effect on the perovskite (Nd, Sr) MnO3 single crystals Jun Takeuchi*, Seitaro Hirahara, Tara P. Dhakal, Kiyotaka Miyoshi, Kenji Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The effect of Cr-doping on the Mn site in Nd1ySryMnO3 (y ¼ 0:5 and 0.55) single crystals grown by the floating zone method has been studied. The y ¼ 0:5 mother material exhibits a transition at TC ¼ 260 K to be a ferromagnetic metal (FMM) and at TN ¼ 160 K to be an antiferromagnetic insulator (AFMI). The doping of 5 at% Cr3+ ions lowers TC to be 250 K and completely suppresses the AFMI. The y ¼ 0:55 mother material exhibits a transition at TN ¼ 230 K to be an antiferromagnetic metal . The doping of 5 at% Cr3+ ions changes the state to be similar to y ¼ 0:5 mother material having the FMM and AFMI. The doping of 10 at% Cr3+ ions completely suppresses the AFMI and keeps the FMM. In both cases, small amount of Cr-doping stabilizes the FMM, which is probably caused by provoking the double exchange interaction between Mn3+/Mn4+ pairs. r 2002 Elsevier Science B.V. All rights reserved. PACS: 71.30.th; 75.30.Hx; 75.30.Vn Keywords: Metal–insulator transition; Doping effects; Colossal magnetoresistance; Charge ordering
There has been renewed interest in physical properties of hole-doped perovskite manganites Ln1xAxMnO3, since these materials show exotic electronic transport and magnetic properties [1]. Double exchange (DE) interactions between Mn3+/Mn4+ pairs and the lattice distortion are believed to play an important role for the properties of these materials. Though many works have been done through doping of the Ln sites, far fewer studies have been made in doping Mn sites, which are at the heart of the DE [2,3]. Recently, it has been revealed that a small amount of Cr-doping on the Mn site in Ln0.5Ca0.5MnO3 has a strong influence on the magnetic and electronic properties [4–7]. In this work, we have undertaken a study of the effect of Cr-doping in Nd1ySryMn1xCrxO3 single crystals with y ¼ 0:5 and 0.55 grown by the floating-zone method having been *Corresponding author. Tel.: +81-852-32-6390; fax: +81852-32-6409. E-mail address: [email protected] (J. Takeuchi).
useful for doped single crystals Nd0.67Sr0.33Mn1xMxO3 (M=Fe, Co) [8,9]. The temperature dependence of the magnetization measured by the SQUID magnetometer for Nd1ySryMn1xCrxO3 at a field of 0.1 T is shown in Fig. 1. The mother material for y ¼ 0:5 system shows a ferromagnetic transition at TC ¼ 260 K and then an antiferromagnetic transition at TN ¼ 160 K accompanied with abrupt increase and decrease of the magnetization as lowering temperatures. The doping of 5 at% Cr3+ ions lowers TC to be 250 K, and keeps the ferromagnetic state to the lowest temperature (10 K) measured suppressing completely the antiferromagnetic state. The mother material for y ¼ 0:55 system shows an antiferromagnetic transition at TN ¼ 230 K, where a small peak appears in the magnetization. The doping of 5 at% Cr3+ ions changes the magnetic state to be similar to y ¼ 0:5 mother material having TC ¼ 250 K and TN ¼ 140 K. The doping of 10 at% Cr3+ ions raises TC to be 260 K, and keeps the ferromagnetic state to the lowest temperature measured.
0921-4526/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 0 1 ) 0 1 2 2 2 - 4
J. Takeuchi et al. / Physica B 312–313 (2002) 754–756
(a) y =0.5
Nd1-ySryMn1-xCrxO3
1
x=0.05 H=0.1T
M [µ B/f.u.]
0.5
Open Symbols: ZFC Closed Symbols: FC
x=0
0
(b)y=0.55 x=0.1
1
x=0.05
0.5 0
x=0
0
100
200
T [K]
300
Fig. 1. Temperature dependence of the magnetization for Nd1ySryMn1xCrxO3 at a field of 0.1 T.
104 102
ρ [ Ω · cm]
10
(a) y=0.5
Nd1-ySryMn1-xCrxO3
Closed Symbols: 0T Open Symbols: 7T
0
10-1 10-2
x=0
10-3
x=0.05
10-2
(b) y=0.55
x=0.05
10-1
10-2
10-2
x=0
10-3
10-3
x=0.1
10-4
10-4
0
100
T [K]
Fig. 2. Temperature dependence Nd1ySryMn1xCrxO3.
200 of
the
keeping the FMM state in accordance with the magnetization data. It should be noted that the colossal magnetoresistance (CMR) near TC for Cr-doped material is bigger than undoped mother material. The resistivity for y ¼ 0:55 mother material shows metallic behavior below TN ; indicating that this material is antiferromagnetic metal (AFMM), though the resistivity increases slowly at lower temperatures. The resistivity for 5 at% Cr-doped material shows similar behavior to y ¼ 0:5 mother material with FMM and AFMI state. The resistivity for 10 at% Cr-doped material shows metallic conduction below TC keeping the FMM state. The temperature dependence of the linear thermal expansion (LTE) measured by the strain gauge method for Nd1ySryMn1xCrxO3 is shown in Fig. 3. The LTE for y ¼ 0:5 mother material changes drastically at TN probably due to the drastic change in lattice parameters which should be related with the appearance of the spin-, charge- and orbital-ordered state below TN : The temperature where the drastic change of LTE appears is lowered by 60 K under the 7 T magnetic field similar to the temperature dependence of the resistivity behavior. The doping of 5 at% Cr3+ ions completely removes the drastic change of LTE and makes clearer an anomaly near TC : This anomaly is suppressed by the 7 T magnetic field. The LTE for y ¼ 0:55 system also shows gradual decrease below TC and abrupt reduction below TN : These experimental results indicate that Cr3+ ions doped at Mn3+ site has an effect of breaking the spin, charge and orbital ordering in the AFMI state formed by the arrangement of Mn3+ and Mn4+ ions. This is probably due to the stability of Cr3+ ions and isoelectricity of Cr3+ with Mn4+. In this situation, DE interaction between Mn3+/Mn4+ pairs should become effective, which will stabilize the FMM state.
10-5 300 resistivity
755
Nd1-ySryMn1-xCrxO3
for
0.001
(a) y=0.5
x=0 x =0.05
∆ L/ L
The temperature dependence of the resistivity for Nd1ySryMn1xCrxO3 is shown in Fig. 2. The resistivity for y ¼ 0:5 mother material shows metallic behavior below Tc and abrupt increase below TN indicating that this material changes from ferromagnetic metal (FMM) to antiferromagnetic insulator (AFMI) through TN : This AFMI state is believed to be spin-, charge- and orbital-ordered state [10]. The applied magnetic field of 7 T lowers TN by 60 K, which consequently leads that the resistivity at 125 K becomes small by 5 orders of magnitude under 7 T field. The resistivity for 5 at% Cr-doped material shows metallic conduction below TC
Closed Symbols: 0T Open Symbols: 7T
(b) y =0.55 0.001
x =0.05 x=0 x=0.1
0
100
T [K]
200
300
Fig. 3. Temperature dependence of the linear thermal expansion for Nd1ySryMn1xCrxO3.
756
J. Takeuchi et al. / Physica B 312–313 (2002) 754–756
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, World Scientific, Singapore, 1998. [2] K.H. Ahn, X.W. Wu, K. Liu, C.L. Chien, Phys. Rev. B 54 (1996) 15299. [3] N. Gayathri, A.K. Raychaudhuri, S.K. Tiwary, R. Gundakaram, A. Arulraj, C.N.R. Rao, Phys. Rev. B 56 (1997) 1345. [4] B. Raveau, A. Maignan, C. Martin, J. Solid State Chem. 130 (1997) 162.
[5] F. Damay, C. Martin, A. Maignan, M. Hervieu, B. Raveau, F. Bouree, G. Andre, Appl. Phys. Lett. 73 (1998) 3772. [6] T. Kimura, Y. Tomioka, R. Kumai, Y. Okimoto, Y. Tokura, Phys. Rev. Lett. 83 (1999) 3940. [7] Y. Moritomo, A. Machida, S. Mori, N. Yamamoto, A. Nakamura, Phys. Rev. B 60 (1999) 9220. [8] J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, J. Magn. Magn. Mater. 226–230 (2001) 884. [9] T.P. Dhakal, K. Miyoshi, K. Fujiwara, J. Takeuchi, J. Magn. Magn. Mater. 226–230 (2001) 824. [10] H. Kuwahara, Y. Tomioka, A. Asamitsu, Y. Moritomo, Y. Tokura, Science 270 (1995) 961.