- Email: [email protected]
Structural and magnetic properties of Sr2RuO4-type oxides
Journal of Magnetism and Magnetic Materials 140-144 (1995) 179-180
ELSEVIER
Structuralandmagneticpropertiesof Sr,RuO,-typeoxides J.L. Martinez aS*, C. Prieto a, J. Rodriguez-Carvajal b, A. de And& M. Vallet-Regi ‘, J.M. Gonz6lez-Calbet d
a,
de Ciencia de Materiales de Madrti CSIC Fat. Ciencias {C-4), Cantobhco, Madrid E-28049, Spain b Laboratoire LGon Brillouin (Cl%-CNRli)), CE-Saclay, F-91191 Gifsur Yvette &a& France ’ Dy Quimica Inorghica y Bioinorghica, Fat. Farmacia, Universidad Compiutense, Madrid E-28040, Spain Dep. Quimica Inorghica, Fat. Ciencias Quimicas, Universidad Complutenw, MadrtX E-28040, Spain
a htituto
Abstract We have studied the structure and magnetic properties of the Sr,-,Ca,RuO, oxides, as well as those of the map perovskite precursors, i.e. Sr,RuO, and CaRuG,. The Sr,RuO, compound presents a tetragonal structure (u = 3.9 A, c = 12.7 & space group I4/mmm) isomorphous to the prototype K,NiF,. SrRu03 shows a ferromagnetic transition at Tc = 170 K. The magnetic susceptibility of CaRuO, seems to indicate an antiferromagnetic behavior, with a clear deviation from the Curie-Weiss law below - 70 K. However, neutron diffraction data at 1.5 K preclude the existence of long range antiferromagnetic ordering in CaRuO,. The magnetic behaviour of SrzRuO, indicates a very weak dependence on temperature of the magnetic susceptibility, close to a Pauli paramagnet.
Perovskite-related metal oxides have been studied since a long time, but a renewed interest is rising, due to the discovery of superconductivity in this type of compounds. The Ru oxides (ARuO,) were fiit characterized by ferromagnetism at T, = 160 K for SrRuO, and by antiferromagnetism at TN = 110 K for CaRuO, [l-3]. Later, the structure of both compoundswasstudiedby singlecrystal X-ray diffraction showing a cubic structure for SrRuO, (space group Pm3) and orthorhomic for CaRuOJ (Pbnm) [4]. The data for Sr,RuO, are scarce and not conclusive. Magnetically the signal is dominated by a ferromagnetic SrRuO, impurity. Transport measurements show metallic conductivity [1,3]. We decided to study these oxides for the metallic behavior and the K,Nii,-type structure. Our aim was to introduce Ca2’ in order to produce a tilt in the RuG6 octahedra (tilted orthorhombic structure), still maintaining metallic conductivity which could give rise to structural phase transitions at low temperature similar to those in cuprates and nickelates. The samples were prepared by the ceramic method at 1200°C during 120 h. Neutron diffraction data were obtained at the Lab. L. Brillouin, Saclay, on the DlA highresolution powder diffractometer sited on the neutron guide. The Rietveld method was used to analyze the crystal structure, using the program FULLPROF [5]. The magnetic susceptibility was measured in a SQUID magnetome-
* Corresponding author. Fax: t 34-l-397-8579; email: [email protected]. 0304-8853/95/$09.50
ter (MPMS-SS from Quantun Design) in a temperature range of 1.7-400 K and applied magnetic field up to 5 T. The structural data for Sr,RuO, are presented in Fig. 1
0
,....I....g....I..-.r....l....( 10.0
6ao
OS.0
IiO.0
1x0 a0
1603
(‘I
Fig. 1. Neutron powder diffraction data (a) at RT for Sr,RuO, and (b) at 1.5 K for CaRuO,. Points represent the raw data, the solid line is the calculated profile and the hnver profile is the difference. The marks indicate the allowed reflections. For CaRu0~ the reflections corresponding to A/2 are also included.
Cl 1995 Elsevier Science B.V. All rights reserved
SSDI 0304-8853(94)01245-f!
35.0
180
3.L. Marther et al. /Journal
of Magnetism and Magnetic Materials 140-144 (19951 iZ-IPi2
and Table 1. Sr,RuO, presents a tetragonal structure (i4/mmm) and no contamination from SrRuO, is observable for the detection limit of 0.5% in our neutron diffraction experiment. We have also prepared a sample of nominal composition Sr,.,Ca,.,RuO, (5% substitution), in order to induce a structural phase transition from tetragonal to orthorhombic, due to the different ionic sizes of Ca and Sr. Neutron diffraction data show that the occupation factor for Ca goes close to zero, indicating that Sr substitution did not take place. We have measured the CaRuO, perovskite at low temperature looking for Bragg peaks coming from the long range antiferromagnetic ordering (Fig. 1~). The conclusion is negative at 1.5 K. The extra peaks observed come from a small contamination of the harmonics h/2 (0.15% in integrated intensity), Calculations show that if there were some ordering, the ordered magnetic moment should be lower than 0.05~~. Our conclusion is similar to that obtained from recent data of perturbed angular correlation spectroscopy on CaRuO, [6], where the AF ordering at 77 K was disregarded. The crystal structure is well described in the space group Pbnm, also at low temperature; see Table 1. The temperature dependence of the magnetic susceptibility is presented in Fig. 2, Even if no ferromagnetic SrRuOs contamination was observed by neutron powder diffraction, ik impurity is cieariy detected in our susceptibility measurements. This is especially favorable due to the intrinsic low signal coming from SrzRuO,. Comparing with the signal of pure SrRuO, (see inset of Fig. 2) we have estimated the perovskite contamination in Sr,RuO, Table 1 Structural parameters for Sr,RuG, and CaRuO, Sr, RuO,
CaRuO,
CaRuOj
300 3.87049(7)
1.5 5.3508(2) 5.5299(3) 7.6580(3)
12.7339(4)
300 5.3663(Z) 5X71(3) 7.6708(3)
14/mmm 1
Pbnm 4
t 0.3527(3)
n 0.9865(9) y 0.0539(6)
Ru o(1) Moz) o(l) (xv:)
@OO) 2 0.1607(3)
($00) x 0.0912(6) y 0.47w5)
o(2)
ol;o>
x 0.6992(4) y 0.2973(4) z O&488(3) 1.9842(g)
T (K)
a (A) b (A,
c
(23 byfl
o(2) (Xyz) Ru-O(l)
!A,
Ru-M2) (A> Ru-Of21 (A> Bragg R-factor
X2
2.046t5)
Pbnm
4 0.9&74(9) 0.0564(5) ($00) 0.0931(5)
0.4727(5) 0.69&l(4) 0.2975(3) 0.0489(3)
1.9352(l)
1.995(Z) 1.999(2)
1.9838(g) l-994(2) 1.999f2)
2.93 6.7
4*1 2.66 56 2.578
4.3 8.42 55 2.578
Nr. reflections
27
A
2.448
2.0 i 0
100
Temperature
200
(K)
300
Fig. 2. Temperature dependence of the magnetic susceptibility for Sr,RuO,, impurity.
after subtraction of the signal from the small SrRuO, Insets: temperature dependence of magnetization for
pure SrRuO,, and inverse susceptibility for CaRuO,. as 0.02%, well below the sensiti-ity of neutron powder diffraction. in order to extrai: the magnetic susceptibility from SrzRuO, at low temperature (below 160 K, T, from SrRuO,) we have measured the isothermal hy;ieresis curve (M vs. H) and obtained the derivative from the high field portion. This high field differential susceptibility is independent of the small ferromagnetic contamination. Fig. 2 shows a very weak temperature dependence of the magnetic susceptibility in the temperature range 5-300 K This is close to that expected for Pauli paramagnetism coming from the collective behavior of the Ru d-electrons. The results for Sr,.,Caa,,RuO, are almost identical to that of SrzRuO,, as expected. Finally, we show in the inset of Fig. 2 the temperature dependence of the inverse magnetic susceptibility for CaRuO,. As pointed out previously, there is a clear departure from the Curie-Weiss behavior below 70 K [l], but after the neutron diffraction experiments no long range antiferromaguetic ordering is observed at 1.5 K. This departure from linearity is probably due to short range antiferromagnetic correlations that, however, do not Froduce long range ordering even at 1.5 K. Acknowledgemenf: This work was supported by CICyT under project MAT93-793 and CAM93-141. References [l] A. Callaghan, C.W. Mreller and R. Ward, Inorg. Chem. 5
(1966) 1572. I21 J.M. Longo, P.M. Raccah and J.B. Geodenough, J. Appl. Phys. 39 (1968) 1327. [3] C.N.R. Rao, P. Ganguly, KK Singh and R.A. Mohan Ram, J. Solid State Chem. 7 (1988) 14. 141 W. Bensch, H. Schmalle and A. Reller, Solid State lonics 43 @90) 171.
[5] I, Rodriguez-Carvajal. Physica B 192 (1993) 55. (61 G.L. Catchen, T.M. Rearick and D.G. Schlom, Phys. Rev. B 49 (1994) 318.
ELSEVIER
Structuralandmagneticpropertiesof Sr,RuO,-typeoxides J.L. Martinez aS*, C. Prieto a, J. Rodriguez-Carvajal b, A. de And& M. Vallet-Regi ‘, J.M. Gonz6lez-Calbet d
a,
de Ciencia de Materiales de Madrti CSIC Fat. Ciencias {C-4), Cantobhco, Madrid E-28049, Spain b Laboratoire LGon Brillouin (Cl%-CNRli)), CE-Saclay, F-91191 Gifsur Yvette &a& France ’ Dy Quimica Inorghica y Bioinorghica, Fat. Farmacia, Universidad Compiutense, Madrid E-28040, Spain Dep. Quimica Inorghica, Fat. Ciencias Quimicas, Universidad Complutenw, MadrtX E-28040, Spain
a htituto
Abstract We have studied the structure and magnetic properties of the Sr,-,Ca,RuO, oxides, as well as those of the map perovskite precursors, i.e. Sr,RuO, and CaRuG,. The Sr,RuO, compound presents a tetragonal structure (u = 3.9 A, c = 12.7 & space group I4/mmm) isomorphous to the prototype K,NiF,. SrRu03 shows a ferromagnetic transition at Tc = 170 K. The magnetic susceptibility of CaRuO, seems to indicate an antiferromagnetic behavior, with a clear deviation from the Curie-Weiss law below - 70 K. However, neutron diffraction data at 1.5 K preclude the existence of long range antiferromagnetic ordering in CaRuO,. The magnetic behaviour of SrzRuO, indicates a very weak dependence on temperature of the magnetic susceptibility, close to a Pauli paramagnet.
Perovskite-related metal oxides have been studied since a long time, but a renewed interest is rising, due to the discovery of superconductivity in this type of compounds. The Ru oxides (ARuO,) were fiit characterized by ferromagnetism at T, = 160 K for SrRuO, and by antiferromagnetism at TN = 110 K for CaRuO, [l-3]. Later, the structure of both compoundswasstudiedby singlecrystal X-ray diffraction showing a cubic structure for SrRuO, (space group Pm3) and orthorhomic for CaRuOJ (Pbnm) [4]. The data for Sr,RuO, are scarce and not conclusive. Magnetically the signal is dominated by a ferromagnetic SrRuO, impurity. Transport measurements show metallic conductivity [1,3]. We decided to study these oxides for the metallic behavior and the K,Nii,-type structure. Our aim was to introduce Ca2’ in order to produce a tilt in the RuG6 octahedra (tilted orthorhombic structure), still maintaining metallic conductivity which could give rise to structural phase transitions at low temperature similar to those in cuprates and nickelates. The samples were prepared by the ceramic method at 1200°C during 120 h. Neutron diffraction data were obtained at the Lab. L. Brillouin, Saclay, on the DlA highresolution powder diffractometer sited on the neutron guide. The Rietveld method was used to analyze the crystal structure, using the program FULLPROF [5]. The magnetic susceptibility was measured in a SQUID magnetome-
* Corresponding author. Fax: t 34-l-397-8579; email: [email protected]. 0304-8853/95/$09.50
ter (MPMS-SS from Quantun Design) in a temperature range of 1.7-400 K and applied magnetic field up to 5 T. The structural data for Sr,RuO, are presented in Fig. 1
0
,....I....g....I..-.r....l....( 10.0
6ao
OS.0
IiO.0
1x0 a0
1603
(‘I
Fig. 1. Neutron powder diffraction data (a) at RT for Sr,RuO, and (b) at 1.5 K for CaRuO,. Points represent the raw data, the solid line is the calculated profile and the hnver profile is the difference. The marks indicate the allowed reflections. For CaRu0~ the reflections corresponding to A/2 are also included.
Cl 1995 Elsevier Science B.V. All rights reserved
SSDI 0304-8853(94)01245-f!
35.0
180
3.L. Marther et al. /Journal
of Magnetism and Magnetic Materials 140-144 (19951 iZ-IPi2
and Table 1. Sr,RuO, presents a tetragonal structure (i4/mmm) and no contamination from SrRuO, is observable for the detection limit of 0.5% in our neutron diffraction experiment. We have also prepared a sample of nominal composition Sr,.,Ca,.,RuO, (5% substitution), in order to induce a structural phase transition from tetragonal to orthorhombic, due to the different ionic sizes of Ca and Sr. Neutron diffraction data show that the occupation factor for Ca goes close to zero, indicating that Sr substitution did not take place. We have measured the CaRuO, perovskite at low temperature looking for Bragg peaks coming from the long range antiferromagnetic ordering (Fig. 1~). The conclusion is negative at 1.5 K. The extra peaks observed come from a small contamination of the harmonics h/2 (0.15% in integrated intensity), Calculations show that if there were some ordering, the ordered magnetic moment should be lower than 0.05~~. Our conclusion is similar to that obtained from recent data of perturbed angular correlation spectroscopy on CaRuO, [6], where the AF ordering at 77 K was disregarded. The crystal structure is well described in the space group Pbnm, also at low temperature; see Table 1. The temperature dependence of the magnetic susceptibility is presented in Fig. 2, Even if no ferromagnetic SrRuOs contamination was observed by neutron powder diffraction, ik impurity is cieariy detected in our susceptibility measurements. This is especially favorable due to the intrinsic low signal coming from SrzRuO,. Comparing with the signal of pure SrRuO, (see inset of Fig. 2) we have estimated the perovskite contamination in Sr,RuO, Table 1 Structural parameters for Sr,RuG, and CaRuO, Sr, RuO,
CaRuO,
CaRuOj
300 3.87049(7)
1.5 5.3508(2) 5.5299(3) 7.6580(3)
12.7339(4)
300 5.3663(Z) 5X71(3) 7.6708(3)
14/mmm 1
Pbnm 4
t 0.3527(3)
n 0.9865(9) y 0.0539(6)
Ru o(1) Moz) o(l) (xv:)
@OO) 2 0.1607(3)
($00) x 0.0912(6) y 0.47w5)
o(2)
ol;o>
x 0.6992(4) y 0.2973(4) z O&488(3) 1.9842(g)
T (K)
a (A) b (A,
c
(23 byfl
o(2) (Xyz) Ru-O(l)
!A,
Ru-M2) (A> Ru-Of21 (A> Bragg R-factor
X2
2.046t5)
Pbnm
4 0.9&74(9) 0.0564(5) ($00) 0.0931(5)
0.4727(5) 0.69&l(4) 0.2975(3) 0.0489(3)
1.9352(l)
1.995(Z) 1.999(2)
1.9838(g) l-994(2) 1.999f2)
2.93 6.7
4*1 2.66 56 2.578
4.3 8.42 55 2.578
Nr. reflections
27
A
2.448
2.0 i 0
100
Temperature
200
(K)
300
Fig. 2. Temperature dependence of the magnetic susceptibility for Sr,RuO,, impurity.
after subtraction of the signal from the small SrRuO, Insets: temperature dependence of magnetization for
pure SrRuO,, and inverse susceptibility for CaRuO,. as 0.02%, well below the sensiti-ity of neutron powder diffraction. in order to extrai: the magnetic susceptibility from SrzRuO, at low temperature (below 160 K, T, from SrRuO,) we have measured the isothermal hy;ieresis curve (M vs. H) and obtained the derivative from the high field portion. This high field differential susceptibility is independent of the small ferromagnetic contamination. Fig. 2 shows a very weak temperature dependence of the magnetic susceptibility in the temperature range 5-300 K This is close to that expected for Pauli paramagnetism coming from the collective behavior of the Ru d-electrons. The results for Sr,.,Caa,,RuO, are almost identical to that of SrzRuO,, as expected. Finally, we show in the inset of Fig. 2 the temperature dependence of the inverse magnetic susceptibility for CaRuO,. As pointed out previously, there is a clear departure from the Curie-Weiss behavior below 70 K [l], but after the neutron diffraction experiments no long range antiferromaguetic ordering is observed at 1.5 K. This departure from linearity is probably due to short range antiferromagnetic correlations that, however, do not Froduce long range ordering even at 1.5 K. Acknowledgemenf: This work was supported by CICyT under project MAT93-793 and CAM93-141. References [l] A. Callaghan, C.W. Mreller and R. Ward, Inorg. Chem. 5
(1966) 1572. I21 J.M. Longo, P.M. Raccah and J.B. Geodenough, J. Appl. Phys. 39 (1968) 1327. [3] C.N.R. Rao, P. Ganguly, KK Singh and R.A. Mohan Ram, J. Solid State Chem. 7 (1988) 14. 141 W. Bensch, H. Schmalle and A. Reller, Solid State lonics 43 @90) 171.
[5] I, Rodriguez-Carvajal. Physica B 192 (1993) 55. (61 G.L. Catchen, T.M. Rearick and D.G. Schlom, Phys. Rev. B 49 (1994) 318.