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Appearance of two magnetic phases in doped Lu1−xAxFeO3(A=Ca,Sr)
Physica B 329–333 (2003) 745–746
Appearance of two magnetic phases in doped Lu1xAx FeO3 ðA ¼ Ca; SrÞ Michio Takahashi, Hideaki Takano*, Shigeyuki Murayama Department of Materials Science and Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan
Abstract The effect of Ca and Sr substitution for Lu in polycrystalline samples of LuFeO3 has been studied by means of X-ray diffraction, specific heat and magnetization measurements. Lu1x Cax FeO3 for xp0:2 and Lu1x Srx FeO3 for xp0:1 crystallize into the same orthorhombic structure as LuFeO3 : The peak of the specific heat caused by antiferromagnetic transition for Lu0:9 Ca0:1 FeO3 (LCFO) and Lu0:9 Sr0:1 FeO3 (LSFO) is seen around 590 K and 620 K; respectively. Temperature dependence of the magnetization for LCFO and LSFO also shows rapid changes around 480 K and 605 K; and 525 K and 625 K; respectively. M–H measurements indicate that LCFO below 480 K and LSFO below 525 K are ferromagnetic. These typical changes of the specific heat and the magnetization suggest the appearance of two magnetic ordered phases in the doped Lu1x Ax FeO3 ðA ¼ Ca; SrÞ system. r 2003 Elsevier Science B.V. All rights reserved. Keywords: Phase transition; Career doping; Lu1x Cax FeO3 ; Lu1x Srx FeO3
The rare-earth orthoferrites LaFeO3 and LuFeO3 have a common atomic arrangement and crystallize with the orthorhombic distortion of the perovskite structure [1]. Recently, charge ordering phenomena and magnetic transition are observed in La1x Srx FeO3 [2]. Though La atom has no 4f electron and Lu atom has a closed 4f electron shell, both atoms have a common characteristic in the point that there is no effect of 4f electron. Then we have investigated magnetic and electric effects of carrier doping in LuFeO3 : In this paper we reports two-steps magnetic transition in this carrier doping system. Starting materials used in this study were Fe2 O3 ; Lu2 O3 ; CaCO3 and SrCO3 powder. Mechanical milling was carried out to mix the weighed amount of the powder well and to pre-synthesize for 24 h in a vibrating frame using a hardened steel vial and a 50 mm diameter steel ball. The mixture, in compressed tablet, was sintered in air at 12001C for 24 h: The tablet was mechanically milled for 12 h again, and then the powder was pressed into a disk. Finally this disk was fired again
*Corresponding author. Fax: +81-143-46-5625. E-mail address: [email protected] (H. Takano).
at 12001C for 24 h in an atmosphere and subsequently cooled to room temperature. The structures of Lu1x Ax FeO3 ðA ¼ Ca; SrÞ were characterized by conventional X-ray powder diffraction with Cu Ka radiation and refined by a Rietveld refinement method. Magnetization measurements were carried out between 10 and 750 K in a field of 10 kOe by SQUID magnetometer. A light-chopped AC calorimeter was used to measure relative changes of specific heat from 300 to 840 K: Fig. 1 shows the X-ray diffraction patterns of LuFeO3 (LFO), CaFeO3 (CFO), SrFeO3 (SFO), Lu0:9 Ca0:1 FeO3 (LCFO) and Lu0:9 Sr0:1 FeO3 (LSFO), which are nominal composition. The compounds LFO and CFO are ( b ¼ 5:554 A; ( c¼ orthorhombic with a ¼ 5:217 A; ( and a ¼ 5:594 A; ( b ¼ 5:431 A; ( c ¼ 14:774 A; ( 7:565 A respectively, and belong to the space group Pnma. The ( is space group of SFO, which is cubic with a ¼ 3:863 A; consistent with Pm3% m: We obtained single phases of Lu1x Cax FeO3 for xp0:2 and Lu1x Srx FeO3 for xp0:1; which crystallized into the same orthorhombic structure as LuFeO3 : The obvious difference of lattice constants among LFO, LCFO and LSFO could not be confirmed from Rietveld refinement. It seems that a
0921-4526/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4526(02)02485-7
M. Takahashi et al. / Physica B 329–333 (2003) 745–746
746
0.2 Lu0.9Sr0.1FeO3
1
M (emu/g)
113 321
141 311
132
122
103
040 202
212
221 131
220 112
022
204
230
121 002
200
111
101
LuFeO3
011
Intensity (arb. units)
Lu0.9Sr0.1FeO3 0.8
H =10kOe
Temperature (K) LuFeO3
143
0 300
H=10kOe
400
500
600
700
Temperature (K)
Fig. 2. DC magnetization upon cooling in a 10 kOe magnetic field for Lu1x Cax FeO3 and Lu1x Srx FeO3 : The inset shows MðTÞ curves of CaFeO3 and SrFeO3 in a same field.
60
Fig. 1. X-ray-diffraction patterns of Lu1x Cax FeO3 Lu1x Srx FeO3 recorded with Cu Ka radiation.
CaFeO3
0.12
0.6
341
033
50
0.14
0.1 300 400 500 600 700
0.2
181 331
152 222 080
202
40 2θ (deg.)
0.16
and
chemical pressure effect is very small in these doped LFO system at least for xp0:1: Fig. 2 shows the temperature dependence of magnetization MðTÞ with decreasing temperature for these five samples. The inset shows MðTÞ of CFO and SFO. The increase of MðTÞ upon cooling of LFO, LCFO, LSFO and CFO are seen at about 625 K; 605 K; 625 K and 710 K; respectively. In SFO the peak of the magnetization is shown at 630 K: (These temperatures are denoted by TN :) Fig. 3 shows the specific heat Cp ðTÞ of these five samples between 300 and 750 K: The peak of Cp ðTÞ of all samples is seen around TN : These anomalies of MðTÞ and Cp ðTÞ indicates the existence of a magnetic phase transition at TN : Treves [1] and White [3] reported that LuFeO3 was a canted antiferromagnets with TC ¼ 625 K: Then we conclude this magnetic phase transition at TN is a canted antiferromagnetic or an antiferromagnetic transition. Another abrupt increase of MðTÞ at about 480 and 525 K ðTC Þ upon cooling with no anomaly in Cp ðTÞ is observed for LCFO and LSFO, respectively. Arrott plots obtained from M–H measurements at various temperatures indicate the existence of the spontaneous magnetization only below TC for LCFO and LSFO. From preliminary measurements of the resistivity for the five samples between 80 and 280 K; it was observed that the resistivity of LCFO and LSFO became much smaller than LFO and the temperature dependence of the resistivity for LCFO and LSFO was semiconductive. It is suggested that the Ca and Sr substitution for Lu in LFO results in carrier doping to LFO. Then we conclude that the secondary increase of
SrFeO3
Lu0.9Sr0.1FeO3
Cp (arb. units)
30
161
002 200 141 051 220 102 151 112 042 231
131
111 031 121 040
101
20
Lu0.9Ca0.1FeO3
SrFeO3
0.4
Lu0.9Ca0.1FeO3
CaFeO3
0.18
M (emu/g)
211
210
100
111
200
110
1.2
SrFeO3
LuFeO3
Lu0.9Ca0.1FeO3
CaFeO3
300
400
500
600
700
Temperature (K)
Fig. 3. Specific heat of Lu1x Cax FeO3 and Lu1x Srx FeO3 : The arrow shows the temperature at which MðTÞ shows rapid increase or peak.
MðTÞ for LCFO and LSFO suggest the existence of a ferromagnetic or a ferrimagnetic transition induced by carrier doping.
References [1] D. Treves, J. Appl. Phys. B 26 (1970) 2008. [2] J.Q. Li, Y. Matsui, S.K. Park, Y. Tokura, Phys. Rev. Lett. 79 (1997) 297; T. Ishikawa, S.K. Park, T. Katsufuji, T. Arima, Y. Tokura, Phys. Rev. B 58 (1998) R13326. [3] R.L. White, J. Appl. Phys. 40 (1969) 1061.
Appearance of two magnetic phases in doped Lu1xAx FeO3 ðA ¼ Ca; SrÞ Michio Takahashi, Hideaki Takano*, Shigeyuki Murayama Department of Materials Science and Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585, Japan
Abstract The effect of Ca and Sr substitution for Lu in polycrystalline samples of LuFeO3 has been studied by means of X-ray diffraction, specific heat and magnetization measurements. Lu1x Cax FeO3 for xp0:2 and Lu1x Srx FeO3 for xp0:1 crystallize into the same orthorhombic structure as LuFeO3 : The peak of the specific heat caused by antiferromagnetic transition for Lu0:9 Ca0:1 FeO3 (LCFO) and Lu0:9 Sr0:1 FeO3 (LSFO) is seen around 590 K and 620 K; respectively. Temperature dependence of the magnetization for LCFO and LSFO also shows rapid changes around 480 K and 605 K; and 525 K and 625 K; respectively. M–H measurements indicate that LCFO below 480 K and LSFO below 525 K are ferromagnetic. These typical changes of the specific heat and the magnetization suggest the appearance of two magnetic ordered phases in the doped Lu1x Ax FeO3 ðA ¼ Ca; SrÞ system. r 2003 Elsevier Science B.V. All rights reserved. Keywords: Phase transition; Career doping; Lu1x Cax FeO3 ; Lu1x Srx FeO3
The rare-earth orthoferrites LaFeO3 and LuFeO3 have a common atomic arrangement and crystallize with the orthorhombic distortion of the perovskite structure [1]. Recently, charge ordering phenomena and magnetic transition are observed in La1x Srx FeO3 [2]. Though La atom has no 4f electron and Lu atom has a closed 4f electron shell, both atoms have a common characteristic in the point that there is no effect of 4f electron. Then we have investigated magnetic and electric effects of carrier doping in LuFeO3 : In this paper we reports two-steps magnetic transition in this carrier doping system. Starting materials used in this study were Fe2 O3 ; Lu2 O3 ; CaCO3 and SrCO3 powder. Mechanical milling was carried out to mix the weighed amount of the powder well and to pre-synthesize for 24 h in a vibrating frame using a hardened steel vial and a 50 mm diameter steel ball. The mixture, in compressed tablet, was sintered in air at 12001C for 24 h: The tablet was mechanically milled for 12 h again, and then the powder was pressed into a disk. Finally this disk was fired again
*Corresponding author. Fax: +81-143-46-5625. E-mail address: [email protected] (H. Takano).
at 12001C for 24 h in an atmosphere and subsequently cooled to room temperature. The structures of Lu1x Ax FeO3 ðA ¼ Ca; SrÞ were characterized by conventional X-ray powder diffraction with Cu Ka radiation and refined by a Rietveld refinement method. Magnetization measurements were carried out between 10 and 750 K in a field of 10 kOe by SQUID magnetometer. A light-chopped AC calorimeter was used to measure relative changes of specific heat from 300 to 840 K: Fig. 1 shows the X-ray diffraction patterns of LuFeO3 (LFO), CaFeO3 (CFO), SrFeO3 (SFO), Lu0:9 Ca0:1 FeO3 (LCFO) and Lu0:9 Sr0:1 FeO3 (LSFO), which are nominal composition. The compounds LFO and CFO are ( b ¼ 5:554 A; ( c¼ orthorhombic with a ¼ 5:217 A; ( and a ¼ 5:594 A; ( b ¼ 5:431 A; ( c ¼ 14:774 A; ( 7:565 A respectively, and belong to the space group Pnma. The ( is space group of SFO, which is cubic with a ¼ 3:863 A; consistent with Pm3% m: We obtained single phases of Lu1x Cax FeO3 for xp0:2 and Lu1x Srx FeO3 for xp0:1; which crystallized into the same orthorhombic structure as LuFeO3 : The obvious difference of lattice constants among LFO, LCFO and LSFO could not be confirmed from Rietveld refinement. It seems that a
0921-4526/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4526(02)02485-7
M. Takahashi et al. / Physica B 329–333 (2003) 745–746
746
0.2 Lu0.9Sr0.1FeO3
1
M (emu/g)
113 321
141 311
132
122
103
040 202
212
221 131
220 112
022
204
230
121 002
200
111
101
LuFeO3
011
Intensity (arb. units)
Lu0.9Sr0.1FeO3 0.8
H =10kOe
Temperature (K) LuFeO3
143
0 300
H=10kOe
400
500
600
700
Temperature (K)
Fig. 2. DC magnetization upon cooling in a 10 kOe magnetic field for Lu1x Cax FeO3 and Lu1x Srx FeO3 : The inset shows MðTÞ curves of CaFeO3 and SrFeO3 in a same field.
60
Fig. 1. X-ray-diffraction patterns of Lu1x Cax FeO3 Lu1x Srx FeO3 recorded with Cu Ka radiation.
CaFeO3
0.12
0.6
341
033
50
0.14
0.1 300 400 500 600 700
0.2
181 331
152 222 080
202
40 2θ (deg.)
0.16
and
chemical pressure effect is very small in these doped LFO system at least for xp0:1: Fig. 2 shows the temperature dependence of magnetization MðTÞ with decreasing temperature for these five samples. The inset shows MðTÞ of CFO and SFO. The increase of MðTÞ upon cooling of LFO, LCFO, LSFO and CFO are seen at about 625 K; 605 K; 625 K and 710 K; respectively. In SFO the peak of the magnetization is shown at 630 K: (These temperatures are denoted by TN :) Fig. 3 shows the specific heat Cp ðTÞ of these five samples between 300 and 750 K: The peak of Cp ðTÞ of all samples is seen around TN : These anomalies of MðTÞ and Cp ðTÞ indicates the existence of a magnetic phase transition at TN : Treves [1] and White [3] reported that LuFeO3 was a canted antiferromagnets with TC ¼ 625 K: Then we conclude this magnetic phase transition at TN is a canted antiferromagnetic or an antiferromagnetic transition. Another abrupt increase of MðTÞ at about 480 and 525 K ðTC Þ upon cooling with no anomaly in Cp ðTÞ is observed for LCFO and LSFO, respectively. Arrott plots obtained from M–H measurements at various temperatures indicate the existence of the spontaneous magnetization only below TC for LCFO and LSFO. From preliminary measurements of the resistivity for the five samples between 80 and 280 K; it was observed that the resistivity of LCFO and LSFO became much smaller than LFO and the temperature dependence of the resistivity for LCFO and LSFO was semiconductive. It is suggested that the Ca and Sr substitution for Lu in LFO results in carrier doping to LFO. Then we conclude that the secondary increase of
SrFeO3
Lu0.9Sr0.1FeO3
Cp (arb. units)
30
161
002 200 141 051 220 102 151 112 042 231
131
111 031 121 040
101
20
Lu0.9Ca0.1FeO3
SrFeO3
0.4
Lu0.9Ca0.1FeO3
CaFeO3
0.18
M (emu/g)
211
210
100
111
200
110
1.2
SrFeO3
LuFeO3
Lu0.9Ca0.1FeO3
CaFeO3
300
400
500
600
700
Temperature (K)
Fig. 3. Specific heat of Lu1x Cax FeO3 and Lu1x Srx FeO3 : The arrow shows the temperature at which MðTÞ shows rapid increase or peak.
MðTÞ for LCFO and LSFO suggest the existence of a ferromagnetic or a ferrimagnetic transition induced by carrier doping.
References [1] D. Treves, J. Appl. Phys. B 26 (1970) 2008. [2] J.Q. Li, Y. Matsui, S.K. Park, Y. Tokura, Phys. Rev. Lett. 79 (1997) 297; T. Ishikawa, S.K. Park, T. Katsufuji, T. Arima, Y. Tokura, Phys. Rev. B 58 (1998) R13326. [3] R.L. White, J. Appl. Phys. 40 (1969) 1061.