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Mössbauer study of 57Fe-doped La2SrCu2O6
Nuclear Instruments North-Holland
and Methods
in Physics Research
B76 (1993) 341-342 Beam Interactions with Materials A Atoms
Miissbauer study of 57Fe-doped La,SrCu,O, Yoshihiko Takano a, Takuya Okada b, Sumiko Noro a and Tokio Yamadaya a ’ Department of Physics, Yokohama City Vniuersity, 22-2, Seto, Kanazawa-ku, Yokohama 236. Japan ’ The Institute of Physical and Chemical Research, Wako, Saitama 351-01. Japan
O,OsOh were measured at various temperatures between 372 and 5 K. The spectrum The MGssbauer spectra of La,SrCu,,,57Fe measured at room temperature consists of two paramagnetic quadrupole doublets with similar Miissbauer parameters. The values sites. The spectrum measured at 5 K of IS and small quadrupole splitting values indicate that high spin Fe-” ions are in octahedral consists of a broad sextet and a minor paramagnetic component. The distribution function of H,, shows two peaks of 520 and at 440 kOe. The magnetic susceptibility shows no distinct anomaly in this temperature range. Magnetic ordering seems to take place over a wide range of temperature.
3. Results and discussions
1. Introduction
The 2126 cuprates La,MCu,O,(M:Ca, Sr) have a simple crystal structure composed of double layered two dimensional CuO, pyramids [l]. For the Ca-based compounds synthesized under a high pressure oxygen atmosphere, superconducting transition was observed at 60 K [2,3]. On the other hand, the Sr-based analogue, La,SrCu,O,, exhibited a metallic behavior without superconducting transition [4]. It was pointed out that this difference was closely related to the difference in the local structure [.5-71: e.g. the presence of oxygen between CuO, layers and ordering of large cations, La and M. In the present paper, the results of Mijssbauer and magnetic measurements of 57Fe-doped La,SrCu,_,Fe,O,+, are reported.
The Miissbauer spectra of La,SrCu,~&7Feo,os06 measured at various temperatures are shown in fig. 1. General feature of the spectra is in accord with that of C. Meyer et al. [8,9], except that the magnetic transition was observed at higher temperature in our study.
:i: ; ;.
95
-loo ------?:rs t :.
2. Experimental
296K
!
5
96
iI z
100
258
. . .
K
_Jw
s . .
Powdered specimens La,SrCu,.,,“Fe,,,,O, were prepared by a solid state reaction. Stoichiometric mixture of La,O,, SrCO,, CuO and 57Fe,0, were calcined at 900-1000°C in air. The fired pellets were reground and refired again until the single phase specimens were obtained. The powder X-ray diffraction pattern shows only a 2126 phase, and no impurity phase was observed. The Miissbauer spectra were measured in the temperature range between 5 to 372 K. The magnetic susceptibilities were measured from room temperature to 4.2K by a SQUID magnetometer. 0168-583X/93/$06.00
0 1993 - Elsevier
Science
Publishers
;: )_
. .
t
SOK
5K
-10
I
I
0
Cl0
VELOCITY
Fig. 1. MGssbauer B.V. All rights reserved
spectra
(mm/s)
at various
temperatures.
342
Y. Takano et al. / Study of 57Fe-doped La,SrCu,06
I
I
I
200
I
I
400
I
,
600
tihf ( KOe 1 Fig. 2. Distribution of H,, at SK.
In the paramagnetic state the spectrum is asymetric quadrupole doublet with a small splitting of A = 0.4 mm/s. The spectra could be analyzed into two symmetric quadrupole doublets: sites A and B. The Isomer shift (IS), quadrupole splitting (A) and absorption area (%) are summarized as follows; (a)
IS = 0.305
mm/s,
A = 0.461
(62.5%);
(b)
IS =0.210
mm/s,
A =0.349
(37.5%).
Similarity of the Mossbauer parameters suggest that the two sites have similar surroundings. Both A and B sites will be octahedral sites, and iron are in high spin Fe3+ state. The small values of A are compatible with the calculated values of A by Meyer et al. [8] for Fe3+ octahedra single or Fe3+ pair in the two connected provided by the intercalated oxygen between the CuO, layers. The IS of site B is somewhat reduced as compared with the IS of typical Fe3+ in a octahedron. This reduction could be caused by the increase of the hole density in the 3d orbitals of Fe3+ as in the case of La,_,Sr,CuO, [lo]. The spectrum at 5K consists of two components; minor paramagnetic doublet and magnetic broad sextet, which indicates distribution of Hi,,.
As is shown in fig. 2, the derived distribution function of H,, exhibit two peaks around 520 and 440 KOe, the values are typical of Fe3+ in high spin states. When the temperature rises, the paramagnetic part grows gradually with a simultaneous decrease of the magnetic parts, and becomes paramagnetic around the room temperature. The magnetic susceptibility does not exhibit any distinct anomaly in the same temperature range. The distribution of H,, and broadend magnetic transition are explained by the presence of oxygen between CuO, layers. At the Fe3+ sites, CuO, layers are coupled through the strong 180” superexchange interactions via Fe3+-O-Fe3+ or Fe3+-O-Cu2+ which cause a wide distribution of exchange field and the H,,. If the distribution of Fe3+ and inter-layer oxygen are inhomogeneous, the superparamagnetic behavior will be expected.
References L. Er-Rakho, C. Michel, J. Choisnet and B. Raveau. Mater. Res. Bull. 15 (1980) 897. [2] R.J. Cava et al., Nature 345 (1990) 602. [3] K. Kinoshita, H. Shibata and T. Yamada, Jpn. J. Appl. Phys. 29 (1990) L1632. [4] J.B. Torrance, Y. Tokura, A. Nazzal and S.S.P. Parkin, [l] N. Nguyen,
Phys. Rev. Lett. 60 (1988) 542. [5] V. Caignaert, N. Nugyen and B. Raveau, Mater. Res. Bull. 25 (1990) 199. [6] P. Lightfoot, Shiyou Pei, J.D. Jorgensen, X.X. Tang, A. Manthiram and J.B. Goodenough, Physica Cl69 (1990) 464. [7] K. Kinoshita, H. Shibata and T. Yamada, Physica Cl76 (1991) 433. [8] C. Meyer, F. Hartmann-Boutron, Y. Gros and P. Strobel, Physica Cl81 (1991) 1. [9] F. Hartmann-Boutron, Y. Gros, C. Meyer, P. Strobe1 and J.L. Tholence, J. Magn. Magn. Mater. 104-107 (1992) 501. [lo] P. Imbert, G. Jehanno, P. Debray, C. Garcin and J.A. Hodges, J. Phys. I France 2 (1992) 1405.
and Methods
in Physics Research
B76 (1993) 341-342 Beam Interactions with Materials A Atoms
Miissbauer study of 57Fe-doped La,SrCu,O, Yoshihiko Takano a, Takuya Okada b, Sumiko Noro a and Tokio Yamadaya a ’ Department of Physics, Yokohama City Vniuersity, 22-2, Seto, Kanazawa-ku, Yokohama 236. Japan ’ The Institute of Physical and Chemical Research, Wako, Saitama 351-01. Japan
O,OsOh were measured at various temperatures between 372 and 5 K. The spectrum The MGssbauer spectra of La,SrCu,,,57Fe measured at room temperature consists of two paramagnetic quadrupole doublets with similar Miissbauer parameters. The values sites. The spectrum measured at 5 K of IS and small quadrupole splitting values indicate that high spin Fe-” ions are in octahedral consists of a broad sextet and a minor paramagnetic component. The distribution function of H,, shows two peaks of 520 and at 440 kOe. The magnetic susceptibility shows no distinct anomaly in this temperature range. Magnetic ordering seems to take place over a wide range of temperature.
3. Results and discussions
1. Introduction
The 2126 cuprates La,MCu,O,(M:Ca, Sr) have a simple crystal structure composed of double layered two dimensional CuO, pyramids [l]. For the Ca-based compounds synthesized under a high pressure oxygen atmosphere, superconducting transition was observed at 60 K [2,3]. On the other hand, the Sr-based analogue, La,SrCu,O,, exhibited a metallic behavior without superconducting transition [4]. It was pointed out that this difference was closely related to the difference in the local structure [.5-71: e.g. the presence of oxygen between CuO, layers and ordering of large cations, La and M. In the present paper, the results of Mijssbauer and magnetic measurements of 57Fe-doped La,SrCu,_,Fe,O,+, are reported.
The Miissbauer spectra of La,SrCu,~&7Feo,os06 measured at various temperatures are shown in fig. 1. General feature of the spectra is in accord with that of C. Meyer et al. [8,9], except that the magnetic transition was observed at higher temperature in our study.
:i: ; ;.
95
-loo ------?:rs t :.
2. Experimental
296K
!
5
96
iI z
100
258
. . .
K
_Jw
s . .
Powdered specimens La,SrCu,.,,“Fe,,,,O, were prepared by a solid state reaction. Stoichiometric mixture of La,O,, SrCO,, CuO and 57Fe,0, were calcined at 900-1000°C in air. The fired pellets were reground and refired again until the single phase specimens were obtained. The powder X-ray diffraction pattern shows only a 2126 phase, and no impurity phase was observed. The Miissbauer spectra were measured in the temperature range between 5 to 372 K. The magnetic susceptibilities were measured from room temperature to 4.2K by a SQUID magnetometer. 0168-583X/93/$06.00
0 1993 - Elsevier
Science
Publishers
;: )_
. .
t
SOK
5K
-10
I
I
0
Cl0
VELOCITY
Fig. 1. MGssbauer B.V. All rights reserved
spectra
(mm/s)
at various
temperatures.
342
Y. Takano et al. / Study of 57Fe-doped La,SrCu,06
I
I
I
200
I
I
400
I
,
600
tihf ( KOe 1 Fig. 2. Distribution of H,, at SK.
In the paramagnetic state the spectrum is asymetric quadrupole doublet with a small splitting of A = 0.4 mm/s. The spectra could be analyzed into two symmetric quadrupole doublets: sites A and B. The Isomer shift (IS), quadrupole splitting (A) and absorption area (%) are summarized as follows; (a)
IS = 0.305
mm/s,
A = 0.461
(62.5%);
(b)
IS =0.210
mm/s,
A =0.349
(37.5%).
Similarity of the Mossbauer parameters suggest that the two sites have similar surroundings. Both A and B sites will be octahedral sites, and iron are in high spin Fe3+ state. The small values of A are compatible with the calculated values of A by Meyer et al. [8] for Fe3+ octahedra single or Fe3+ pair in the two connected provided by the intercalated oxygen between the CuO, layers. The IS of site B is somewhat reduced as compared with the IS of typical Fe3+ in a octahedron. This reduction could be caused by the increase of the hole density in the 3d orbitals of Fe3+ as in the case of La,_,Sr,CuO, [lo]. The spectrum at 5K consists of two components; minor paramagnetic doublet and magnetic broad sextet, which indicates distribution of Hi,,.
As is shown in fig. 2, the derived distribution function of H,, exhibit two peaks around 520 and 440 KOe, the values are typical of Fe3+ in high spin states. When the temperature rises, the paramagnetic part grows gradually with a simultaneous decrease of the magnetic parts, and becomes paramagnetic around the room temperature. The magnetic susceptibility does not exhibit any distinct anomaly in the same temperature range. The distribution of H,, and broadend magnetic transition are explained by the presence of oxygen between CuO, layers. At the Fe3+ sites, CuO, layers are coupled through the strong 180” superexchange interactions via Fe3+-O-Fe3+ or Fe3+-O-Cu2+ which cause a wide distribution of exchange field and the H,,. If the distribution of Fe3+ and inter-layer oxygen are inhomogeneous, the superparamagnetic behavior will be expected.
References L. Er-Rakho, C. Michel, J. Choisnet and B. Raveau. Mater. Res. Bull. 15 (1980) 897. [2] R.J. Cava et al., Nature 345 (1990) 602. [3] K. Kinoshita, H. Shibata and T. Yamada, Jpn. J. Appl. Phys. 29 (1990) L1632. [4] J.B. Torrance, Y. Tokura, A. Nazzal and S.S.P. Parkin, [l] N. Nguyen,
Phys. Rev. Lett. 60 (1988) 542. [5] V. Caignaert, N. Nugyen and B. Raveau, Mater. Res. Bull. 25 (1990) 199. [6] P. Lightfoot, Shiyou Pei, J.D. Jorgensen, X.X. Tang, A. Manthiram and J.B. Goodenough, Physica Cl69 (1990) 464. [7] K. Kinoshita, H. Shibata and T. Yamada, Physica Cl76 (1991) 433. [8] C. Meyer, F. Hartmann-Boutron, Y. Gros and P. Strobel, Physica Cl81 (1991) 1. [9] F. Hartmann-Boutron, Y. Gros, C. Meyer, P. Strobe1 and J.L. Tholence, J. Magn. Magn. Mater. 104-107 (1992) 501. [lo] P. Imbert, G. Jehanno, P. Debray, C. Garcin and J.A. Hodges, J. Phys. I France 2 (1992) 1405.