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Praseodymium-deficiency effects upon physical properties of bulk Pr0.6Sr0.4MnO3 manganite
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239 www.elsevier.com/locate/jmmm
Praseodymium-deficiency effects upon physical properties of bulk Pr0:6 Sr0:4MnO3 manganite W. Cheikhrouhou-Koubaaa,, M. Koubaaa, A. Cheikhrouhoua,b,, K. Shimizuc a
Laboratoire de Physique des Mate´riaux, Faculte´ des Sciences de Sfax, B.P. 802, Sfax, Tunisia b Laboratoire Louis NEEL, CNRS, B.P. 166, 38042 Grenoble cedex 9, France c Facuty of Science, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan Available online 27 November 2006
Abstract Structural, magnetic and 55Mn spin-echo NMR properties of praseodymium-deficient Pr0:6x &x Sr0:4 MnO3 compounds (x ¼ 0–0.2) have been investigated. Our synthesized samples have been elaborated using the conventional solid state reaction at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. With decreasing temperature, the stoichiometric Pr0:6 Sr0:4 MnO3 sample exhibits a paramagnetic–ferromagnetic transition above room temperature. Praseodymium deficiency leads to a decrease of the Curie temperature T C . 55Mn spin-echo NMR measurements have also been done at 4.2 K in order to clarify the microscopic characterization of Pr0:6x &x Sr0:4 MnO3 . For Pr deficient samples, several peaks have been observed around 380 MHz, which suggests that the structure in the spectrum originate from inhomogeneous local magnetic states introduced by the Pr deficiency. r 2006 Elsevier B.V. All rights reserved. PACS: 75.47.m; 76.60.Lz Keywords: Manganites; NMR; Spin-echo; Magnetization; Lacunar
Mixed-valent manganites with perovskite structure have attracted considerable attention due to the discovery of colossal magnetoresistance (CMR) effect and potential technological applications for various functional devices [1]. These oxides have a rich, complex and still underdebate physics that is related to the competing electronlattice and electron-electron interactions. The present study is a continuation of our systematic investigations on the effect of presence of a cationic vacancy on the A-site of the perovskite lattice cell. Previous studies on A-site deficient Pr0:7 Sr0:3 MnO3 (PSMO) samples have shown an increase of T C in Pr-deficient compounds (Pr0:7x &x Sr0:3 MnO3 with 0:05oxo0:2) [2], and a decrease of T C in Sr-deficient ones ðPr0:7 Sr0:3x &x MnO3 with xp0:2) [3]. Corresponding authors. Laboratoire de Physique des Mate´riaux, Faculte´ des Sciences de Sfax, B.P. 802, Sfax, Tunisia. Tel./fax: +216 74 676607. E-mail address: [email protected] (W. Cheikhrouhou-Koubaa).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.1084
Pr0:6x &x Sr0:4 MnO3 powder samples with x ¼ 0, 0.05, 0.1, 0.15 and 0.2 were synthesized using the solid state reaction at high temperature. Phase purity, homogeneity and cell dimensions were checked by powder X-ray diffraction (XRD). Magnetization measurements versus temperature in the range 10–350 K were carried out using a vibrating sample magnetometer. 55Mn spin-echo NMR measurements have been carried out using frequency swept spin-echo apparatus at 4.2 K. X-ray powder diffraction at room temperature shows that all our samples are single phase with no detectable secondary phases and crystallize in the orthorhombic structure with Pbnm space group. We present in Fig. 1 the observed and calculated XRD patterns for the sample with x ¼ 0:05 (Open circles represent the observed patterns; continuous lines represent calculated and difference patterns. Thick marks correspond to the position of the allowed Bragg positions). The lattice parameters were ˚ b ¼ 5:4779 A ˚ and c ¼ 7:6577 A. ˚ found to be a ¼ 5:4351 A, With increasing deficiency content, the unit cell volume
ARTICLE IN PRESS W. Cheikhrouhou-Koubaa et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239
e238
30 25
Intensity (a.u.)
M (a.u)
Yobs Ycalc Yobs-Ycala Bragg-position
20 15
x=0 x = 0.05
10
x = 0.1 x = 0.15
5
x = 0.2
0 0
50
100
150
200
250
300
350
T (K) 5
10
15
20
25
30
35
40
45
50
2θ (ο)
Fig. 2. Magnetization evolution versus temperature at 500 Oe for Pr0:6x &x Sr0:4 MnO3 .
Fig. 1. Refinement X-ray diffraction patterns of Pr0:55 Sr0:4 MnO3 at room temperature.
decreases. Detailed results of the structural refinements will be published elsewhere [4]. In Fig. 2 we present the temperature dependance of the magnetzation under an applied field of 500 Oe. With decreasing temperature, all our samples exhibit a paramagnetic–ferromagnetic transition. The Curie temperature T C decreases from 320 K for x ¼ 0 to 254 K, for x ¼ 0:2. With increasing deficiency content, the magnetization decrease observed in the parent compound below 100 K shifts to higher temperature and disappears for x ¼ 0:2. 55 Mn spin-echo NMR measurements have been done at 4.2 K in order to clarify the microscopic characterization of Pr deficient compounds Pr0:6x &x Sr0:4 MnO3 . For ferromagnetic metallic state in a mixed valence manganite, a single broad line is observed because of the fast hopping of eg electron from Mn3þ to Mn4þ . The resonance frequency of the line falls into the frequency range between Mn3þ and Mn4þ lines depending on the hole concentration, which is widely accepted [5,6]. Fig. 3 shows 55Mn NMR spectra of Pr0:6x &x Sr0:4 MnO3 (x ¼ 0:05, 0.15, 0.2) in zero external magnetic field and a field of 1 T, together with that of Pr0:6 Sr0:4 MnO3 . Several peaks, denoted by P1–P5 in Fig. 3, have been observed for the deficient samples. The peaks P1 and P5 correspond to the lines from Mn4þ and Mn3þ in ferromagnetic insulating phases, respectively. These are not observed for the stoichiometric Pr0:6 Sr0:4 MnO3 in ferromagnetic metallic state. The lines at peaks P2, P3 and P4 are attributed to signals from ferromagnetic metallic phases. The line with the peak P4, which is close to that of Pr0:6 Sr0:4 MnO3 , may be attributed to the fast hopping of electrons over whole crystal. The lower line with the peak P3 would arise from the nuclei with different surrounding compared to the line of P4. The metallic lines having such structures might indicate that electron hopping reflects the
Fig. 3. 55Mn NMR spectra of Pr0:6x &x Sr0:4 MnO3 taken at 4.2 K in zerofield (filled circle) and a field of 1 T (open circle), except for x ¼ 0:05. The spectrum for x ¼ 0:05 was taken in a field of 1.5 T. The usual correction was made dividing the intensity of the observed spin-echo at a frequency n by n2 . Zero-field spectrum of stoichiometric Pr0:6 Sr0:4 MnO3 is also shown with dotted line.
local environment around Mn ions, such as fluctuations in Sr concentration at small scale, introduced by Pr deficiency. Furthermore, the multi-peak feature might be
ARTICLE IN PRESS W. Cheikhrouhou-Koubaa et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239
attributed to a pinning of domain walls which is induced by the disorder introduced by the deficiency. The shape of spectrum in the field of 1 T clearly differs from that taken in zero field, which suggests that applying the field removes the pinning of domain walls. The multi-peak spectra have also been observed for ferromagnetic metallic Nd1x Srx MnO3 compounds [7]. References [1] A.M. Haghiri-Gosnet, J.-P. Renard, J. Phys. D: Appl. Phys. 36 (2003) R127.
e239
[2] W. Boujelben, A. Cheikh-Rouhou, J. Pierre, D. Abou-Ras, J.P. Renard, K. Shimizu, Physica B 321 (2002) 68. [3] D. Abou-Ras, W. Boujelben, A. Cheikh-Rouhou, J. Pierre, J.P. Renard, L. Reversat, K. Shimizu, J. Magn. Magn. Mater. 233 (2001) 147. [4] W. Cheikhrouhou-Koubaa, M. Koubaa, A. Cheikhrouhou, A.-M. Haghiri-Gosnet, K. Shimizu, unpublished. [5] G. Matsumoto, J. Phys. Soc. Japan 29 (1970) 615. [6] A. Anane, C. Dupas, K. Le Dang, J.-P. Renard, P. Veillet, A.M. de Leon-Guevara, F. Millot, L. Pinsard, A. Revcolevschi, J. Phys. Condens. Matter 7 (1995) 7015. [7] M. Pattabiraman, P. Murugaraj, G. Rangarajan, C. Dimitropoulos, J.-Ph. Ansermet, G. Papavassiliou, G. Balakrishnan, D.McK. Paul, M.R. Lees, Phys. Rev. B 66 (2002) 224415.
Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239 www.elsevier.com/locate/jmmm
Praseodymium-deficiency effects upon physical properties of bulk Pr0:6 Sr0:4MnO3 manganite W. Cheikhrouhou-Koubaaa,, M. Koubaaa, A. Cheikhrouhoua,b,, K. Shimizuc a
Laboratoire de Physique des Mate´riaux, Faculte´ des Sciences de Sfax, B.P. 802, Sfax, Tunisia b Laboratoire Louis NEEL, CNRS, B.P. 166, 38042 Grenoble cedex 9, France c Facuty of Science, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan Available online 27 November 2006
Abstract Structural, magnetic and 55Mn spin-echo NMR properties of praseodymium-deficient Pr0:6x &x Sr0:4 MnO3 compounds (x ¼ 0–0.2) have been investigated. Our synthesized samples have been elaborated using the conventional solid state reaction at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. With decreasing temperature, the stoichiometric Pr0:6 Sr0:4 MnO3 sample exhibits a paramagnetic–ferromagnetic transition above room temperature. Praseodymium deficiency leads to a decrease of the Curie temperature T C . 55Mn spin-echo NMR measurements have also been done at 4.2 K in order to clarify the microscopic characterization of Pr0:6x &x Sr0:4 MnO3 . For Pr deficient samples, several peaks have been observed around 380 MHz, which suggests that the structure in the spectrum originate from inhomogeneous local magnetic states introduced by the Pr deficiency. r 2006 Elsevier B.V. All rights reserved. PACS: 75.47.m; 76.60.Lz Keywords: Manganites; NMR; Spin-echo; Magnetization; Lacunar
Mixed-valent manganites with perovskite structure have attracted considerable attention due to the discovery of colossal magnetoresistance (CMR) effect and potential technological applications for various functional devices [1]. These oxides have a rich, complex and still underdebate physics that is related to the competing electronlattice and electron-electron interactions. The present study is a continuation of our systematic investigations on the effect of presence of a cationic vacancy on the A-site of the perovskite lattice cell. Previous studies on A-site deficient Pr0:7 Sr0:3 MnO3 (PSMO) samples have shown an increase of T C in Pr-deficient compounds (Pr0:7x &x Sr0:3 MnO3 with 0:05oxo0:2) [2], and a decrease of T C in Sr-deficient ones ðPr0:7 Sr0:3x &x MnO3 with xp0:2) [3]. Corresponding authors. Laboratoire de Physique des Mate´riaux, Faculte´ des Sciences de Sfax, B.P. 802, Sfax, Tunisia. Tel./fax: +216 74 676607. E-mail address: [email protected] (W. Cheikhrouhou-Koubaa).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.10.1084
Pr0:6x &x Sr0:4 MnO3 powder samples with x ¼ 0, 0.05, 0.1, 0.15 and 0.2 were synthesized using the solid state reaction at high temperature. Phase purity, homogeneity and cell dimensions were checked by powder X-ray diffraction (XRD). Magnetization measurements versus temperature in the range 10–350 K were carried out using a vibrating sample magnetometer. 55Mn spin-echo NMR measurements have been carried out using frequency swept spin-echo apparatus at 4.2 K. X-ray powder diffraction at room temperature shows that all our samples are single phase with no detectable secondary phases and crystallize in the orthorhombic structure with Pbnm space group. We present in Fig. 1 the observed and calculated XRD patterns for the sample with x ¼ 0:05 (Open circles represent the observed patterns; continuous lines represent calculated and difference patterns. Thick marks correspond to the position of the allowed Bragg positions). The lattice parameters were ˚ b ¼ 5:4779 A ˚ and c ¼ 7:6577 A. ˚ found to be a ¼ 5:4351 A, With increasing deficiency content, the unit cell volume
ARTICLE IN PRESS W. Cheikhrouhou-Koubaa et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239
e238
30 25
Intensity (a.u.)
M (a.u)
Yobs Ycalc Yobs-Ycala Bragg-position
20 15
x=0 x = 0.05
10
x = 0.1 x = 0.15
5
x = 0.2
0 0
50
100
150
200
250
300
350
T (K) 5
10
15
20
25
30
35
40
45
50
2θ (ο)
Fig. 2. Magnetization evolution versus temperature at 500 Oe for Pr0:6x &x Sr0:4 MnO3 .
Fig. 1. Refinement X-ray diffraction patterns of Pr0:55 Sr0:4 MnO3 at room temperature.
decreases. Detailed results of the structural refinements will be published elsewhere [4]. In Fig. 2 we present the temperature dependance of the magnetzation under an applied field of 500 Oe. With decreasing temperature, all our samples exhibit a paramagnetic–ferromagnetic transition. The Curie temperature T C decreases from 320 K for x ¼ 0 to 254 K, for x ¼ 0:2. With increasing deficiency content, the magnetization decrease observed in the parent compound below 100 K shifts to higher temperature and disappears for x ¼ 0:2. 55 Mn spin-echo NMR measurements have been done at 4.2 K in order to clarify the microscopic characterization of Pr deficient compounds Pr0:6x &x Sr0:4 MnO3 . For ferromagnetic metallic state in a mixed valence manganite, a single broad line is observed because of the fast hopping of eg electron from Mn3þ to Mn4þ . The resonance frequency of the line falls into the frequency range between Mn3þ and Mn4þ lines depending on the hole concentration, which is widely accepted [5,6]. Fig. 3 shows 55Mn NMR spectra of Pr0:6x &x Sr0:4 MnO3 (x ¼ 0:05, 0.15, 0.2) in zero external magnetic field and a field of 1 T, together with that of Pr0:6 Sr0:4 MnO3 . Several peaks, denoted by P1–P5 in Fig. 3, have been observed for the deficient samples. The peaks P1 and P5 correspond to the lines from Mn4þ and Mn3þ in ferromagnetic insulating phases, respectively. These are not observed for the stoichiometric Pr0:6 Sr0:4 MnO3 in ferromagnetic metallic state. The lines at peaks P2, P3 and P4 are attributed to signals from ferromagnetic metallic phases. The line with the peak P4, which is close to that of Pr0:6 Sr0:4 MnO3 , may be attributed to the fast hopping of electrons over whole crystal. The lower line with the peak P3 would arise from the nuclei with different surrounding compared to the line of P4. The metallic lines having such structures might indicate that electron hopping reflects the
Fig. 3. 55Mn NMR spectra of Pr0:6x &x Sr0:4 MnO3 taken at 4.2 K in zerofield (filled circle) and a field of 1 T (open circle), except for x ¼ 0:05. The spectrum for x ¼ 0:05 was taken in a field of 1.5 T. The usual correction was made dividing the intensity of the observed spin-echo at a frequency n by n2 . Zero-field spectrum of stoichiometric Pr0:6 Sr0:4 MnO3 is also shown with dotted line.
local environment around Mn ions, such as fluctuations in Sr concentration at small scale, introduced by Pr deficiency. Furthermore, the multi-peak feature might be
ARTICLE IN PRESS W. Cheikhrouhou-Koubaa et al. / Journal of Magnetism and Magnetic Materials 310 (2007) e237–e239
attributed to a pinning of domain walls which is induced by the disorder introduced by the deficiency. The shape of spectrum in the field of 1 T clearly differs from that taken in zero field, which suggests that applying the field removes the pinning of domain walls. The multi-peak spectra have also been observed for ferromagnetic metallic Nd1x Srx MnO3 compounds [7]. References [1] A.M. Haghiri-Gosnet, J.-P. Renard, J. Phys. D: Appl. Phys. 36 (2003) R127.
e239
[2] W. Boujelben, A. Cheikh-Rouhou, J. Pierre, D. Abou-Ras, J.P. Renard, K. Shimizu, Physica B 321 (2002) 68. [3] D. Abou-Ras, W. Boujelben, A. Cheikh-Rouhou, J. Pierre, J.P. Renard, L. Reversat, K. Shimizu, J. Magn. Magn. Mater. 233 (2001) 147. [4] W. Cheikhrouhou-Koubaa, M. Koubaa, A. Cheikhrouhou, A.-M. Haghiri-Gosnet, K. Shimizu, unpublished. [5] G. Matsumoto, J. Phys. Soc. Japan 29 (1970) 615. [6] A. Anane, C. Dupas, K. Le Dang, J.-P. Renard, P. Veillet, A.M. de Leon-Guevara, F. Millot, L. Pinsard, A. Revcolevschi, J. Phys. Condens. Matter 7 (1995) 7015. [7] M. Pattabiraman, P. Murugaraj, G. Rangarajan, C. Dimitropoulos, J.-Ph. Ansermet, G. Papavassiliou, G. Balakrishnan, D.McK. Paul, M.R. Lees, Phys. Rev. B 66 (2002) 224415.