- Email: [email protected]
Charge and spin ordering in (Nd, Sr)MnO3 induced by Cr-doping with oxygen deficiency
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281
Charge and spin ordering in (Nd, Sr)MnO3 induced by Cr-doping with oxygen deficiency J. Takeuchi*, N. Yamane, S. Hirahara, K. Miyoshi, K. Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The effect of Cr-doping on the Mn site in the perovskite Nd1ySryMnO3 (y ¼ 0:5; 0.55 and 0.65) single crystals has been studied. The magnetic and electronic phase diagram has been obtained. Especially, the charge-ordered insulating phase with CE-type spin ordering, which is characteristic for y ¼ 0:5 material, has also been observed in Cr-doped y ¼ 0:55 and 0.65 materials. The results are explained by the antiferromagnetic interaction between Cr and Mn ions together with oxygen deficiency induced by Cr-doping. r 2003 Elsevier B.V. All rights reserved. PACS: 71.30.+h; 75.30.Hx; 75.30.Vn Keywords: Metal–insulator transition; Doping effects; Charge ordering; (Nd,Sr)MnO3
There has been renewed interest in physical properties of hole-doped perovskite manganites Ln1xAxMnO3, since these materials show exotic electronic transport and magnetic properties [1,2]. Double exchange (DE) interactions between Mn3+/Mn4+ pairs and the lattice distortion have been clarified to play an important role for the properties of these materials. Recently, it has been reported that a small amount of Cr-doping on the Mn site in Ln0.5A0.5MnO3 has a strong influence on the magnetic and electronic properties [3–8]. In this work, we have undertaken a study of the effect of Cr-doping in Nd1ySryMn1xCrxO3 (y ¼ 0:5; 0.55 and 0.65) single crystals grown by the floating-zone method. The undoped y ¼ 0:5 material shows successive transition from paramagnetic semiconducting phase (PM) to ferromagnetic metallic phase (F-M) and then to charge-ordered insulating phase with CE-type antiferromagnetic spin ordering (CE-I) [1,2]. The temperature dependence of the magnetization M and the resistivity r for this material (y ¼ 0:5; x ¼ 0) are shown *Corresponding author. Tel.: +81-852-32-6390; fax: +81852-32-6409. E-mail address: [email protected] (J. Takeuchi).
in Fig. 1. Cr-doping above 2 at% completely suppresses the CE-I keeping the F-M down to the lowest temperature measured [7]. The undoped y ¼ 0:55 material shows a transition from PM to A-type antiferromagnetic metallic phase (A-M). It is noticeable that Cr-doping of 5 at% induces successive transition from PM to F-M and to CE-I [8], similar to the undoped y ¼ 0:5 material. The temperature dependence of M and r for this material (y ¼ 0:55; x ¼ 0:05) are shown in Fig. 1. Cr-doping above 7 at% completely suppresses the CE-I keeping the F-M down to the lowest temperature. The undoped y ¼ 0:65 material shows a transition from PM to C-type antiferromagnetic insulating phase (C-I). Cr-doping of 5 and 10 at% induces a transition from PM to A-M similar to the undoped y ¼ 0:55 material. The temperature dependence of M and r for the material with 15 at% Cr (y ¼ 0:65; x ¼ 0:15) are shown in Fig. 1. Same type of successive transition as the undoped y ¼ 0:5 material is observed though the change of M and r near the transition temperature is largely broadened. Cr-doping of 20 at% induces the simple F-M down to the lowest temperature. The average magnetic moment per TM site (Mn or Cr) determined by the magnetization at 10 K under 7 T
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.514
ARTICLE IN PRESS J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281
e280
0.2
Nd1-y SryMn1-x CrxO3
M [µB / f.u.]
1
0. 5
H=0.1T y=0.5 x=0
y=0.55 x=0.05
y=0.65 x=0.15
Nd1-y SryMn1-xCrxO3
F-M
0
ρ [ Ω · cm]
y=0.5 x=0
y=0.55 x=0.05
10
0
10
-1
H=0
x
10 1
0.1
CE-I
y=0.65 x=0.15
10 -2
A-1
10 -3 10 -4
0
100
300
200
C-1
T [K ] Fig. 1. Temperature dependence of the magnetization (upper panel) and the resistivity (lower panel) for Nd1ySryMn1xCrxO3.
0
0.5
0.55
Fig. 3. Magnetic and Nd1ySryMn1xCrxO3.
0.6 y electronic
0.65 phase
0.7 diagram
for
4
Nd1-y SryMn1-xCrxO3
M (µB / f.u.)
3 y=0.05 y=0.55
2
y=0.65 1
0 0
0.1
0.2
x Fig. 2. Average magnetic moment per TM site at 10 K under 7 T as a function of x for Nd1ySryMn1xCrxO3.
as a function of x is shown in Fig. 2. The average moment in the F-M region decreases with increasing x; which means Cr3+ spins are opposite to Mn3+ and Mn4+ spins. These results suggest the mechanism for Cr-induced F-M state. The antiferromagnetic interaction between Cr and Mn ions invokes the ferromagnetic DE interaction between Mn3+/Mn4+ pairs. The F-M phase will be realized when DE interaction overcomes antiferromagnetic super-exchange (SE) interaction between Mn ions. The magnetic and electronic phase diagram in x vs. y is shown in Fig. 3, where solid line is a guide for the eye. This diagram is determined by taking into account not only the data of M and r but also the data of thermal expansion and magnetostriction. For example, thermal expansion data show that the crystal with y ¼ 0:55 and x ¼ 0:05 exhibits large contraction of c-axis and expan-
sion of a-axis at a transition from F-M to CE-I just like the undoped y ¼ 0:5 crystal, which reflects the realization of a characteristic d-electron state 3x2 r2 =3y2 r2 in the CE-I [2]. An extraordinary result is the existence of CE-I phase in Cr-doped materials, which appears in the region that Cr-concentration is nearly equal to the deviation of Sr-concentration from 0.5, i.e. xEy 0:5 shown by the dotted line in Fig. 3. We propose a possible mechanism that CE-I phase is formed in the region (Mn3++Cr3+):Mn4+E1:1 that is realized by substituting Cr3+ not for Mn3+ but for Mn4+ accompanying with oxygen deficiency. Solid lines in Fig. 2, M ¼ 3:5 6x for y ¼ 0:5; M ¼ 3:45 6x for y ¼ 0:55; M ¼ 3:35 6x for y ¼ 0:65; are drown assuming that Cr3+ substituted for Mn4+ couples antiferromagnetically with neighboring Mn ions, which fit the data satisfactorily. In conclusion, the magnetic and electronic phases observed in Cr-doped Nd1ySryMnO3 are explained by the idea that the antiferromagnetic interaction between Cr and Mn ions together with oxygen deficiency induced by Cr-doping strongly affects the competing ferromagnetic DE and antiferromagnetic SE interactions between Mn ions.
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal magnetoresistance, charge ordering and related properties of manganese oxides, World Scientific, Singapore, 1998. [2] Y. Tokura (Ed.), Colossal magnetoresistive oxides, Gordon and Breach, New York, 2000.
ARTICLE IN PRESS J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281 [3] B. Raveau, A. Maignan, C. Martin, J. Solid State Chem. 130 (1997) 162. [4] F. Damay, C. Martin, A. Maignan, M. Hervieu, B. Raveau, F. Bouree, G. Andre, Appl. Phys. Lett. 73 (1998) 3772. [5] T. Kimura, Y. Tomioka, R. Kumai, Y. Okimoto, Y. Tokura, Phys. Rev. Lett. 83 (1999) 3940.
e281
[6] Y. Moritomo, A. Machida, S. Mori, N. Yamamoto, A. Nakamura, Phys. Rev. B 60 (1999) 9220. [7] J. Takeuchi, T.P. Dhakal, S. Hirahara, K. Miyoshi, J. Magn. Magn. Mater. 239 (2002) 173. [8] J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, Physica B 312–313 (2002) 754.
Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281
Charge and spin ordering in (Nd, Sr)MnO3 induced by Cr-doping with oxygen deficiency J. Takeuchi*, N. Yamane, S. Hirahara, K. Miyoshi, K. Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The effect of Cr-doping on the Mn site in the perovskite Nd1ySryMnO3 (y ¼ 0:5; 0.55 and 0.65) single crystals has been studied. The magnetic and electronic phase diagram has been obtained. Especially, the charge-ordered insulating phase with CE-type spin ordering, which is characteristic for y ¼ 0:5 material, has also been observed in Cr-doped y ¼ 0:55 and 0.65 materials. The results are explained by the antiferromagnetic interaction between Cr and Mn ions together with oxygen deficiency induced by Cr-doping. r 2003 Elsevier B.V. All rights reserved. PACS: 71.30.+h; 75.30.Hx; 75.30.Vn Keywords: Metal–insulator transition; Doping effects; Charge ordering; (Nd,Sr)MnO3
There has been renewed interest in physical properties of hole-doped perovskite manganites Ln1xAxMnO3, since these materials show exotic electronic transport and magnetic properties [1,2]. Double exchange (DE) interactions between Mn3+/Mn4+ pairs and the lattice distortion have been clarified to play an important role for the properties of these materials. Recently, it has been reported that a small amount of Cr-doping on the Mn site in Ln0.5A0.5MnO3 has a strong influence on the magnetic and electronic properties [3–8]. In this work, we have undertaken a study of the effect of Cr-doping in Nd1ySryMn1xCrxO3 (y ¼ 0:5; 0.55 and 0.65) single crystals grown by the floating-zone method. The undoped y ¼ 0:5 material shows successive transition from paramagnetic semiconducting phase (PM) to ferromagnetic metallic phase (F-M) and then to charge-ordered insulating phase with CE-type antiferromagnetic spin ordering (CE-I) [1,2]. The temperature dependence of the magnetization M and the resistivity r for this material (y ¼ 0:5; x ¼ 0) are shown *Corresponding author. Tel.: +81-852-32-6390; fax: +81852-32-6409. E-mail address: [email protected] (J. Takeuchi).
in Fig. 1. Cr-doping above 2 at% completely suppresses the CE-I keeping the F-M down to the lowest temperature measured [7]. The undoped y ¼ 0:55 material shows a transition from PM to A-type antiferromagnetic metallic phase (A-M). It is noticeable that Cr-doping of 5 at% induces successive transition from PM to F-M and to CE-I [8], similar to the undoped y ¼ 0:5 material. The temperature dependence of M and r for this material (y ¼ 0:55; x ¼ 0:05) are shown in Fig. 1. Cr-doping above 7 at% completely suppresses the CE-I keeping the F-M down to the lowest temperature. The undoped y ¼ 0:65 material shows a transition from PM to C-type antiferromagnetic insulating phase (C-I). Cr-doping of 5 and 10 at% induces a transition from PM to A-M similar to the undoped y ¼ 0:55 material. The temperature dependence of M and r for the material with 15 at% Cr (y ¼ 0:65; x ¼ 0:15) are shown in Fig. 1. Same type of successive transition as the undoped y ¼ 0:5 material is observed though the change of M and r near the transition temperature is largely broadened. Cr-doping of 20 at% induces the simple F-M down to the lowest temperature. The average magnetic moment per TM site (Mn or Cr) determined by the magnetization at 10 K under 7 T
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.514
ARTICLE IN PRESS J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281
e280
0.2
Nd1-y SryMn1-x CrxO3
M [µB / f.u.]
1
0. 5
H=0.1T y=0.5 x=0
y=0.55 x=0.05
y=0.65 x=0.15
Nd1-y SryMn1-xCrxO3
F-M
0
ρ [ Ω · cm]
y=0.5 x=0
y=0.55 x=0.05
10
0
10
-1
H=0
x
10 1
0.1
CE-I
y=0.65 x=0.15
10 -2
A-1
10 -3 10 -4
0
100
300
200
C-1
T [K ] Fig. 1. Temperature dependence of the magnetization (upper panel) and the resistivity (lower panel) for Nd1ySryMn1xCrxO3.
0
0.5
0.55
Fig. 3. Magnetic and Nd1ySryMn1xCrxO3.
0.6 y electronic
0.65 phase
0.7 diagram
for
4
Nd1-y SryMn1-xCrxO3
M (µB / f.u.)
3 y=0.05 y=0.55
2
y=0.65 1
0 0
0.1
0.2
x Fig. 2. Average magnetic moment per TM site at 10 K under 7 T as a function of x for Nd1ySryMn1xCrxO3.
as a function of x is shown in Fig. 2. The average moment in the F-M region decreases with increasing x; which means Cr3+ spins are opposite to Mn3+ and Mn4+ spins. These results suggest the mechanism for Cr-induced F-M state. The antiferromagnetic interaction between Cr and Mn ions invokes the ferromagnetic DE interaction between Mn3+/Mn4+ pairs. The F-M phase will be realized when DE interaction overcomes antiferromagnetic super-exchange (SE) interaction between Mn ions. The magnetic and electronic phase diagram in x vs. y is shown in Fig. 3, where solid line is a guide for the eye. This diagram is determined by taking into account not only the data of M and r but also the data of thermal expansion and magnetostriction. For example, thermal expansion data show that the crystal with y ¼ 0:55 and x ¼ 0:05 exhibits large contraction of c-axis and expan-
sion of a-axis at a transition from F-M to CE-I just like the undoped y ¼ 0:5 crystal, which reflects the realization of a characteristic d-electron state 3x2 r2 =3y2 r2 in the CE-I [2]. An extraordinary result is the existence of CE-I phase in Cr-doped materials, which appears in the region that Cr-concentration is nearly equal to the deviation of Sr-concentration from 0.5, i.e. xEy 0:5 shown by the dotted line in Fig. 3. We propose a possible mechanism that CE-I phase is formed in the region (Mn3++Cr3+):Mn4+E1:1 that is realized by substituting Cr3+ not for Mn3+ but for Mn4+ accompanying with oxygen deficiency. Solid lines in Fig. 2, M ¼ 3:5 6x for y ¼ 0:5; M ¼ 3:45 6x for y ¼ 0:55; M ¼ 3:35 6x for y ¼ 0:65; are drown assuming that Cr3+ substituted for Mn4+ couples antiferromagnetically with neighboring Mn ions, which fit the data satisfactorily. In conclusion, the magnetic and electronic phases observed in Cr-doped Nd1ySryMnO3 are explained by the idea that the antiferromagnetic interaction between Cr and Mn ions together with oxygen deficiency induced by Cr-doping strongly affects the competing ferromagnetic DE and antiferromagnetic SE interactions between Mn ions.
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal magnetoresistance, charge ordering and related properties of manganese oxides, World Scientific, Singapore, 1998. [2] Y. Tokura (Ed.), Colossal magnetoresistive oxides, Gordon and Breach, New York, 2000.
ARTICLE IN PRESS J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 272-276 (2004) e279–e281 [3] B. Raveau, A. Maignan, C. Martin, J. Solid State Chem. 130 (1997) 162. [4] F. Damay, C. Martin, A. Maignan, M. Hervieu, B. Raveau, F. Bouree, G. Andre, Appl. Phys. Lett. 73 (1998) 3772. [5] T. Kimura, Y. Tomioka, R. Kumai, Y. Okimoto, Y. Tokura, Phys. Rev. Lett. 83 (1999) 3940.
e281
[6] Y. Moritomo, A. Machida, S. Mori, N. Yamamoto, A. Nakamura, Phys. Rev. B 60 (1999) 9220. [7] J. Takeuchi, T.P. Dhakal, S. Hirahara, K. Miyoshi, J. Magn. Magn. Mater. 239 (2002) 173. [8] J. Takeuchi, S. Hirahara, T.P. Dhakal, K. Miyoshi, K. Fujiwara, Physica B 312–313 (2002) 754.