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Dependence of the structural and physical properties of Ru-1212 compound on the thermal treatment and oxygen content
Physica C 408–410 (2004) 187–188 www.elsevier.com/locate/physc
Dependence of the structural and physical properties of Ru-1212 compound on the thermal treatment and oxygen content M.R. Cimberle a
a,*
, R. Masini a, E. Gilioli a, C. Artini b, G.A. Costa b, M. Ferretti b, P. Mele b, A. Martinelli b
CNR-IMEM, Parma e sezione di Genova, c/o Dipartimento di Fisica, Via Dodecaneso 33, 16146 Genova, Italy b INFM LAMIA and DCCI, Via Dodecaneso 31, 16146 Genova, Italy
Abstract We present structural and physical data obtained on Ru (Gd)-1212 compounds submitted, after solid state preparation, to different annealing procedures and thermal treatment. The samples were characterized by XRPD and TEM analysis. In addition structural refinement was performed according to the Rietveld method. Variations of both the superconducting and magnetic properties are presented and discussed. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Superconducting perovskite; Magnetic ordering
The rutheno-cuprate compounds have attracted a lot of interest for the simultaneous presence of superconducting and magnetic ordering. In spite of a great quantity of investigations many questions are still open: we refer to the microstructure, the type of magnetic ordering and the valence state of the ruthenium. As well known, inside a well-defined phenomenology showing a magnetic ordering at about T ¼ 130 K and a superconducting transition at or below T ¼ 45 K, the measured physical properties are strongly ‘‘sample dependent’’. In spite of the variability of the physical properties, the structural characterization of the sample seems to indicate invariability and stability of the structure, where the oxygen stoichiometry is considered substantially stable [1]. To go inside these problems Ru (Gd)-1212 samples (as prepared: AP), synthesized with the standard procedure described in [2], were subjected to different annealing treatments at T ¼ 1060 °C in flowing oxygen for one week (1 W) and one month (1
*
Corresponding author. Tel.: +39-103536448; fax: +39103622790. E-mail address: cimberle@fisica.unige.it (M.R. Cimberle).
M). The samples have been characterized by X-ray powder diffraction (XRPD), followed by Rietveld refinement and Transmission Electron Microscopy (TEM) analysis. In particular TEM analysis evidenced an orthorhombic distortion of the lattice [3]; as a consequence the XRPD data were refined in the Pmmm space group, although the diffraction patterns can successfully indexed in the P4/mmm space group. A strong dependence of the structural properties on thermal treatments is evident (Table 1): in particular cell parameters increase with a consequent increase of the cell volume (of about 0.18%), while the c=a and c=b ratios slightly decrease. In addition a strong variation of the rotation angles h ðha ; hb ; hc Þ of the RuO6 octhaedra has been observed. Also TEM observation reveals strong microstructural variations related to annealing treatments. The AP sample shows the presence of intragranular disordered microdomains as well as extended planar defects; after one week annealing planar defects are still present, whereas domains sizes are strongly increased; after one month annealing also the planar defects are no more detected. The annealing produces a variation of the superconducting transition temperature onset Tc , that is
0921-4534/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.02.076
188
M.R. Cimberle et al. / Physica C 408–410 (2004) 187–188
Table 1 Dependence of some structural and magnetic characteristics on thermal treatment
a (A) b (A) c (A) 3 ) V (A hc ha ; hb Mrem (lB ) Msat (lB )
AP
1W
1M
3.8294(2) 3.8487(2) 11.5018(7) 169.52 15.2 4.7 0.13 7.68
3.8309(2) 3.8517(2) 11.5055(7) 169.77 9.7 5.9 0.15 8.11
3.8314(2) 3.8524(2) 11.5060(7) 169.83 10.6 8.6 0.29 8.42
DO
0.11 8.68 Fig. 2. q vs. T measurements. Inset: temperature derivatives of resistivitiy.
Fig. 1. v vs. T measurements. Inset: temperature derivatives of magnetic suscepibilitity.
pushed toward higher temperatures, and of the entity of the diamagnetic behaviour both in ZFC and FC measurements (Fig. 1). The increase of the transition temperature onset is clearly seen in the resistivity measurements in Fig. 2. The 1 M sample exhibits Tonset greater than 50 K, while the AP sample shows the expected value of T ¼ 45 K. To complete the picture of the observed physical variations we point out that the magnetic ordering temperature (as valued by the cuspid of the ZFC curve) decreases on increasing the annealing time, ranging from T ¼ 129:7 K for the AP sample to T ¼ 126 K in 1 M annealed sample. Other variations are observed in the amplitude of the hysteresis loop measured at T ¼ 5 K and in the saturation magnetization value that we measured at T ¼ 2 K and lo H ¼ 5:5 T. This last variation has been already observed in [1]. The results are shown in Table 1. We looked for an explanation of the observed phenomenology taking into account both the structural ordering induced by the annealing and an oxygen content variation. The microstructural ordering gives a direct explanation of the variations of the su-
perconducting transition both resistively (the resistivity decreases, the semiconducting upturn tends to disappears and the transition width decreases), and magnetically (the diamagnetic signal both in FC and ZFC measurements increases): to explain the variation of Tc we could invoke a decrease of the charge localization but, in the light of all the observed variations, it appears reasonable to suppose that the annealing produces also a variation in the oxygen stoichiometry that drives the physical properties variation. To have hints on this hypothesis we submitted the 1 M sample to a 1 h heating in vacuum (p ¼ 4 105 Torr) at about 600 °C to have an oxygen depleted sample [4]. The sample was cooled in vacuum down to room temperature in about 3 h and measured again. The oxygen depletion (see Fig. 1 and Table 1 as sample DO) moves the superconducting transition toward lower temperature and the magnetic one to higher temperatures. Therefore an oxygen uptake during the annealing is consistent with the observed phenomenology and also with the remanent magnetization variation: one can suppose that the oxygen entry changes the valence state of Ruthenium and that the ‘‘ferromagnetic’’ behaviour due to the ferrimagnetism associated with the Ru lattice in a mixed valence state [5] goes toward higher unsaturated value, while the opposite happens in the de-oxidized sample.
References [1] [2] [3] [4] [5]
P.W. Klamut et al., Physica C 364 (2001) 313. C. Artini et al., Physica C 377 (2002) 431. A. Martinelli et al., Phy. Rev. B 69 (2004) 052507. F. Cordero et al., Phys. Rev. B 67 (2003) 144519. R.S. Liu et al., Phys Rev. B 63 (2001) 212507-1.
Dependence of the structural and physical properties of Ru-1212 compound on the thermal treatment and oxygen content M.R. Cimberle a
a,*
, R. Masini a, E. Gilioli a, C. Artini b, G.A. Costa b, M. Ferretti b, P. Mele b, A. Martinelli b
CNR-IMEM, Parma e sezione di Genova, c/o Dipartimento di Fisica, Via Dodecaneso 33, 16146 Genova, Italy b INFM LAMIA and DCCI, Via Dodecaneso 31, 16146 Genova, Italy
Abstract We present structural and physical data obtained on Ru (Gd)-1212 compounds submitted, after solid state preparation, to different annealing procedures and thermal treatment. The samples were characterized by XRPD and TEM analysis. In addition structural refinement was performed according to the Rietveld method. Variations of both the superconducting and magnetic properties are presented and discussed. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Superconducting perovskite; Magnetic ordering
The rutheno-cuprate compounds have attracted a lot of interest for the simultaneous presence of superconducting and magnetic ordering. In spite of a great quantity of investigations many questions are still open: we refer to the microstructure, the type of magnetic ordering and the valence state of the ruthenium. As well known, inside a well-defined phenomenology showing a magnetic ordering at about T ¼ 130 K and a superconducting transition at or below T ¼ 45 K, the measured physical properties are strongly ‘‘sample dependent’’. In spite of the variability of the physical properties, the structural characterization of the sample seems to indicate invariability and stability of the structure, where the oxygen stoichiometry is considered substantially stable [1]. To go inside these problems Ru (Gd)-1212 samples (as prepared: AP), synthesized with the standard procedure described in [2], were subjected to different annealing treatments at T ¼ 1060 °C in flowing oxygen for one week (1 W) and one month (1
*
Corresponding author. Tel.: +39-103536448; fax: +39103622790. E-mail address: cimberle@fisica.unige.it (M.R. Cimberle).
M). The samples have been characterized by X-ray powder diffraction (XRPD), followed by Rietveld refinement and Transmission Electron Microscopy (TEM) analysis. In particular TEM analysis evidenced an orthorhombic distortion of the lattice [3]; as a consequence the XRPD data were refined in the Pmmm space group, although the diffraction patterns can successfully indexed in the P4/mmm space group. A strong dependence of the structural properties on thermal treatments is evident (Table 1): in particular cell parameters increase with a consequent increase of the cell volume (of about 0.18%), while the c=a and c=b ratios slightly decrease. In addition a strong variation of the rotation angles h ðha ; hb ; hc Þ of the RuO6 octhaedra has been observed. Also TEM observation reveals strong microstructural variations related to annealing treatments. The AP sample shows the presence of intragranular disordered microdomains as well as extended planar defects; after one week annealing planar defects are still present, whereas domains sizes are strongly increased; after one month annealing also the planar defects are no more detected. The annealing produces a variation of the superconducting transition temperature onset Tc , that is
0921-4534/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.02.076
188
M.R. Cimberle et al. / Physica C 408–410 (2004) 187–188
Table 1 Dependence of some structural and magnetic characteristics on thermal treatment
a (A) b (A) c (A) 3 ) V (A hc ha ; hb Mrem (lB ) Msat (lB )
AP
1W
1M
3.8294(2) 3.8487(2) 11.5018(7) 169.52 15.2 4.7 0.13 7.68
3.8309(2) 3.8517(2) 11.5055(7) 169.77 9.7 5.9 0.15 8.11
3.8314(2) 3.8524(2) 11.5060(7) 169.83 10.6 8.6 0.29 8.42
DO
0.11 8.68 Fig. 2. q vs. T measurements. Inset: temperature derivatives of resistivitiy.
Fig. 1. v vs. T measurements. Inset: temperature derivatives of magnetic suscepibilitity.
pushed toward higher temperatures, and of the entity of the diamagnetic behaviour both in ZFC and FC measurements (Fig. 1). The increase of the transition temperature onset is clearly seen in the resistivity measurements in Fig. 2. The 1 M sample exhibits Tonset greater than 50 K, while the AP sample shows the expected value of T ¼ 45 K. To complete the picture of the observed physical variations we point out that the magnetic ordering temperature (as valued by the cuspid of the ZFC curve) decreases on increasing the annealing time, ranging from T ¼ 129:7 K for the AP sample to T ¼ 126 K in 1 M annealed sample. Other variations are observed in the amplitude of the hysteresis loop measured at T ¼ 5 K and in the saturation magnetization value that we measured at T ¼ 2 K and lo H ¼ 5:5 T. This last variation has been already observed in [1]. The results are shown in Table 1. We looked for an explanation of the observed phenomenology taking into account both the structural ordering induced by the annealing and an oxygen content variation. The microstructural ordering gives a direct explanation of the variations of the su-
perconducting transition both resistively (the resistivity decreases, the semiconducting upturn tends to disappears and the transition width decreases), and magnetically (the diamagnetic signal both in FC and ZFC measurements increases): to explain the variation of Tc we could invoke a decrease of the charge localization but, in the light of all the observed variations, it appears reasonable to suppose that the annealing produces also a variation in the oxygen stoichiometry that drives the physical properties variation. To have hints on this hypothesis we submitted the 1 M sample to a 1 h heating in vacuum (p ¼ 4 105 Torr) at about 600 °C to have an oxygen depleted sample [4]. The sample was cooled in vacuum down to room temperature in about 3 h and measured again. The oxygen depletion (see Fig. 1 and Table 1 as sample DO) moves the superconducting transition toward lower temperature and the magnetic one to higher temperatures. Therefore an oxygen uptake during the annealing is consistent with the observed phenomenology and also with the remanent magnetization variation: one can suppose that the oxygen entry changes the valence state of Ruthenium and that the ‘‘ferromagnetic’’ behaviour due to the ferrimagnetism associated with the Ru lattice in a mixed valence state [5] goes toward higher unsaturated value, while the opposite happens in the de-oxidized sample.
References [1] [2] [3] [4] [5]
P.W. Klamut et al., Physica C 364 (2001) 313. C. Artini et al., Physica C 377 (2002) 431. A. Martinelli et al., Phy. Rev. B 69 (2004) 052507. F. Cordero et al., Phys. Rev. B 67 (2003) 144519. R.S. Liu et al., Phys Rev. B 63 (2001) 212507-1.