- Email: [email protected]
Magnetic properties of Pr ions in perovskite-type oxides
Journal of Magnetism and Magnetic Materials 177-- 181 (1998) 541 542
~
Journalof magnetism and magnetic ~ i ~ materials
ELSEVIER
Magnetic properties of Pr ions in perovskite-type oxides K. Sekizawa, M. Kitagawa, Y. Takano* Department of Physics, College of Science and Technology, Nihon UniversiO,. 1-8 Kanda-Surugadai, Chiyoda-ku, To@o 101, Japan
Abstract Magnetic properties of Pr ions with the controlled valence on the A and B sites of perovskite-type oxides (ABO3) were investigated for two systems, PrSc~ -~Mg~O3 and BaPr~ -~Bi~O3. F r o m the magnetic susceptibility X versus temperature T curves of PrScl-xMg~O3, the ;( T curve for molar Pr 3+ ions on the A site and that of Pr 4+ ions were obtained. The 1/x-T curves for both ions exhibit the crystalline electric field (CEF) effect and the effective magnetic moment It~ff above 100 K is 3.41 lab for Pr 3+ and 2.58 lab for Pr 4+, respectively. The Z T curve of PrSco.sMgo.zO3 is similar to that of PrBazCu3Oy. In the BaPrl xBi~O3 system, only one intermediate phase BaPro.sBio.503 exists, in which Pr and Bi take an ordered arrangement on the B site. The magnetic susceptibility 7~ for Pr 4+ and that of Pr 3+ in the ordered arrangement with Bi 5 + on the B site are much smaller than those for the A site, reflecting the strong C E F effect on the B site. Experimental z - T curves can be well reproduced by the numerical calculation for Pr 3+ or Pr 4+ ions in the molecular field and the C E F with proper respective parameters. ~'; 1998 Elsevier Science B.V. All rights reserved.
Keywords: Crystal field - RE compounds; Perovskite structure; Superconductors - high Tc
The valence state of Pr ions in PrBa2Cu3Oy has been receiving considerable interest, because of possible connection with the mechanism of high-T~ superconductivity [1]. The magnetic susceptibility ;( versus temperature T curve of PrBazCu3Oy deviates considerably from that of free Pr 3 + [2] and the valence state of the Pr ion has come into question. In this context, we have studied magnetic properties of Pr ions with a known valence on perovskite lattices, in comparison with those of PrBa2CusOy. Magnetic properties of Pr ions were investigated on two systems, PrScl xMgxO3 and BaPrl_xBixOa. In the former, Pr ions occupy the A site and in the latter, the B site. 1. PrScl-~MgxO3. All samples were prepared by a solid-state reaction. The single-phase samples of PrScl .~MgxO~. with orthorhombic GdFeO3-type struct u r e were obtained by sintering the mixture of stoichiometric amounts of Pr6Oll, SczOs and M g O powders at 1 4 5 0 C in (Ar + H2) gas flow for 0 ~ x ~< 0.2. Except for x = 0, samples were annealed at 500=C for 48 h in 0 2 flow (02 annealing). By the thermogravimetry and the magnetization measurement, it was confirmed that the oxygen content y except for x = 0 was equal to
*Corresponding author. Tel.: + 81 3 3259 0891; fax: + 81 3 3293 8269; e-mail: [email protected].
3 after the 02 annealing. The oxygen content y of PrScOy without the 0 2 annealing is already equal to 3.025. The inverse magnetic susceptibility versus temperature curves 1/Z T for PrSCl xMg~O3, which comes from Pr ions in the A site, are a little convex and have an apparent negative Weiss temperature 0p; that is considered to be the crystalline electric field (CEF) effect (Fig. 1). F r o m the curves for two different compositions, the X T curve for molar Pr 3 + ions on the A site and that of Pr 4 + ions were obtained. The estimated curves from the different pair of x coincide with each other reasonably. The curves in Fig. 2 are the averaged ones. The effective magnetic moment # m in the temperature range 100 K ~ T ~< 300 K is 3.41 lab for Pr 3+ and 2.58 lab for Pr 4+, respectively. The temperature dependence of the magnetic susceptibility of Pr 3 ÷ and Pr 4+ ions was calculated in the framework of Stevens' operator equivalents in the ground states of the J-multiplets. The values of the crystal-field parameters which reproduce the experimental curves are shown in Table 1; the first column for the Pr 3+ ion and the second column for the Pr 4+ ion, respectively. The crystal-field parameters B" are composed of three factors; B~ = A~(r")O,. The 0, are Stevens' coefficients, and the AI~' are lattice coefficients which are considered not to vary so much for Pr 3 + and Pr 4 + ions. Using the Stevens' coefficients and ( r " ) for the Ce 3+ ion and c o m m o n A', the values of the crystal-field parameters for the Pr 4 + ion
0304-8853/98/$19.00 ~" 1998 Elsevier Science B.V. All rights rcserved Pll S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 9 4 7 - 5
542
K. Sekizawa el al. ,/Journal of Magnetism and Magnetic Materials 177 181 (1998) 541 542
Table 1 Crystal-field parameters for
Pr 3 + and
ions
P r 4+
Crystal-field parameters (K)
Pr 3 +
Pr 4 +
B~
0.450
B~
0.650
0,845 0,15 1.12 0.323 5.85
B~ B~
0.245 -- 0.0980
~
1.05
B~ B~ B~ B~
0.00348 0.0140 0.0650 0.00825
Pr 4 + (converted from Pr 3+) 0.860 1,24 -- 2,59 1.03 11,1
250
-~,5 N
0
50
100
150
200
r
2S0
300
(K)
Fig. I. Temperature dependence of the inverse magnetic susceptibility for PrBa2Cu3Oy and PrScl-~Mg.,O3. From upper side, PrBa2Cu3Oy (dotted line), x = 0.2, 0.15, 0.1, 0.05 and 0 (solid lines), respectively. The curves for x = 0 and 0.05 coincide with each other.
are o b t a i n e d from those of the P r 3 + ion. They are s h o w n in the third column. The values in the second c o l u m n agree in sign a n d the order of m a g n i t u d e with those in the third column. This suggests that P r 3+ a n d P r 4+ ions are on the same site, namely, the A site. 2. BaPrl-:~BixO3. In the BaPrx-xBixO3 system, only one intermediate phase BaPr0 sBi0.503 exists, in which the ordered a r r a n g e m e n t of P r a n d Bi ions on the B site is revealed by the superstructure line (0 l 1) in the X-ray diffraction pattern. The m a g n e t i c susceptibility of BaPrO3 which corresponds to Z of P r 4+ on the B site shows an antiferromagnetic ordering below 11 K, which agrees with the previous d a t a [3-6]. T h e magnetic susceptibility of BaPro.sBio.503 c o r r e s p o n d s to P r 3 + ions in an ordered a r r a n g e m e n t with Bi s + ion o n the B site. T h e magnetic susceptibility of P r 3+ a n d P r a+ ions in the B site are m u c h smaller t h a n those in the A site, reflecting the strong C E F at the B site. The magnetism of PrBa2Cu3Oy was previously examined by numerical calculation [7]. The magnetism of PrBa2Cu30>, is similar to that of P r 3 + ion at the A site of perovskite, where a small a m o u n t of P r 4 + ion is introduced (Fig. 1). The 4f energy level of P r ion a n d the energy of p b a n d of the CuO2 plane lie close with each other in PrBa2Cu30>. and the hybridization of 4f orbital a n d the O2p~ orbital of the CuO2 plane is expected. Therefore we suggest that the w f hybridization results in the ~ T behavior similar to that of P r ¢+ mixing. A part of this study was s u p p o r t e d by a G r a n t - i n - A i d for Scientific Research on Priority Areas 'New Development of Rare E a r t h C o m p l e x ' No. 08220262 from the Ministry of Education, Science a n d Culture, Japan.
References 400
....
[ ....
i ....
....
I
i
....
i , , , ,
350
-
Pr4÷ (expenmemal} .
300 250
I'r~" (
c
a
l
c
~
.2. 2~ 150
a< 11~ 50 $0
100
150
i'
200
250
300
(K)
Fig. 2. Temperature dependence of the inverse magnetic susceptibility, of molar Pr 3+ and Pr 4+ estimated from experimental values (solid lines) and calculated ones (dotted lines).
[1] H.B. Radousky, J. Mater. Res. 7 (1992) 1917. [2] A. Kebede, C.S. Jee, J. Schwegler, J.E. Crow, T. Mihalisin, G.H. Myer, R.E. Salomon, P. Schlottmann, M.V. Kuric, S.H. Bloom, R.P. Guertin, Phys. Rev. B 40 (1989) 4453. [3] M. Bickel, G.L. Goodman, L. Soderholm, J. Solid State Chem. 76 (1988) 178. [4] B. Lippold, J. Herrmann, U.-C. Boehnke, H. Boerner, J. Horn, H.-C. Semmelhack, M. Wurlitzer, Solid State Commun. 79 (1991) 487. [5] G. Cao, T. Yuen, P. Permambuco-Wise, J.E. Crow, J.W. O'Reilly, M.V. Kuric, R.P. Guertin, N. Rosov, J.W. Lynn, J. Appl. Phys. 70 (1991) 6332. [6] J.B. Bulman, M.V. Kuric, R.P. Guertin, S. Foner, E.J. McNiff Jr., G. Cao, J. O'Riely, J.E. Crow, P.P. Wise, T. Yuen, J. Appl. Phys. 69 (1991) 4874. [7] Y. Takano, S. Yokoyama, K. Kanno, K. Sekizawa, Physica C 252 (1995) 61.
~
Journalof magnetism and magnetic ~ i ~ materials
ELSEVIER
Magnetic properties of Pr ions in perovskite-type oxides K. Sekizawa, M. Kitagawa, Y. Takano* Department of Physics, College of Science and Technology, Nihon UniversiO,. 1-8 Kanda-Surugadai, Chiyoda-ku, To@o 101, Japan
Abstract Magnetic properties of Pr ions with the controlled valence on the A and B sites of perovskite-type oxides (ABO3) were investigated for two systems, PrSc~ -~Mg~O3 and BaPr~ -~Bi~O3. F r o m the magnetic susceptibility X versus temperature T curves of PrScl-xMg~O3, the ;( T curve for molar Pr 3+ ions on the A site and that of Pr 4+ ions were obtained. The 1/x-T curves for both ions exhibit the crystalline electric field (CEF) effect and the effective magnetic moment It~ff above 100 K is 3.41 lab for Pr 3+ and 2.58 lab for Pr 4+, respectively. The Z T curve of PrSco.sMgo.zO3 is similar to that of PrBazCu3Oy. In the BaPrl xBi~O3 system, only one intermediate phase BaPro.sBio.503 exists, in which Pr and Bi take an ordered arrangement on the B site. The magnetic susceptibility 7~ for Pr 4+ and that of Pr 3+ in the ordered arrangement with Bi 5 + on the B site are much smaller than those for the A site, reflecting the strong C E F effect on the B site. Experimental z - T curves can be well reproduced by the numerical calculation for Pr 3+ or Pr 4+ ions in the molecular field and the C E F with proper respective parameters. ~'; 1998 Elsevier Science B.V. All rights reserved.
Keywords: Crystal field - RE compounds; Perovskite structure; Superconductors - high Tc
The valence state of Pr ions in PrBa2Cu3Oy has been receiving considerable interest, because of possible connection with the mechanism of high-T~ superconductivity [1]. The magnetic susceptibility ;( versus temperature T curve of PrBazCu3Oy deviates considerably from that of free Pr 3 + [2] and the valence state of the Pr ion has come into question. In this context, we have studied magnetic properties of Pr ions with a known valence on perovskite lattices, in comparison with those of PrBa2CusOy. Magnetic properties of Pr ions were investigated on two systems, PrScl xMgxO3 and BaPrl_xBixOa. In the former, Pr ions occupy the A site and in the latter, the B site. 1. PrScl-~MgxO3. All samples were prepared by a solid-state reaction. The single-phase samples of PrScl .~MgxO~. with orthorhombic GdFeO3-type struct u r e were obtained by sintering the mixture of stoichiometric amounts of Pr6Oll, SczOs and M g O powders at 1 4 5 0 C in (Ar + H2) gas flow for 0 ~ x ~< 0.2. Except for x = 0, samples were annealed at 500=C for 48 h in 0 2 flow (02 annealing). By the thermogravimetry and the magnetization measurement, it was confirmed that the oxygen content y except for x = 0 was equal to
*Corresponding author. Tel.: + 81 3 3259 0891; fax: + 81 3 3293 8269; e-mail: [email protected].
3 after the 02 annealing. The oxygen content y of PrScOy without the 0 2 annealing is already equal to 3.025. The inverse magnetic susceptibility versus temperature curves 1/Z T for PrSCl xMg~O3, which comes from Pr ions in the A site, are a little convex and have an apparent negative Weiss temperature 0p; that is considered to be the crystalline electric field (CEF) effect (Fig. 1). F r o m the curves for two different compositions, the X T curve for molar Pr 3 + ions on the A site and that of Pr 4 + ions were obtained. The estimated curves from the different pair of x coincide with each other reasonably. The curves in Fig. 2 are the averaged ones. The effective magnetic moment # m in the temperature range 100 K ~ T ~< 300 K is 3.41 lab for Pr 3+ and 2.58 lab for Pr 4+, respectively. The temperature dependence of the magnetic susceptibility of Pr 3 ÷ and Pr 4+ ions was calculated in the framework of Stevens' operator equivalents in the ground states of the J-multiplets. The values of the crystal-field parameters which reproduce the experimental curves are shown in Table 1; the first column for the Pr 3+ ion and the second column for the Pr 4+ ion, respectively. The crystal-field parameters B" are composed of three factors; B~ = A~(r")O,. The 0, are Stevens' coefficients, and the AI~' are lattice coefficients which are considered not to vary so much for Pr 3 + and Pr 4 + ions. Using the Stevens' coefficients and ( r " ) for the Ce 3+ ion and c o m m o n A', the values of the crystal-field parameters for the Pr 4 + ion
0304-8853/98/$19.00 ~" 1998 Elsevier Science B.V. All rights rcserved Pll S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 9 4 7 - 5
542
K. Sekizawa el al. ,/Journal of Magnetism and Magnetic Materials 177 181 (1998) 541 542
Table 1 Crystal-field parameters for
Pr 3 + and
ions
P r 4+
Crystal-field parameters (K)
Pr 3 +
Pr 4 +
B~
0.450
B~
0.650
0,845 0,15 1.12 0.323 5.85
B~ B~
0.245 -- 0.0980
~
1.05
B~ B~ B~ B~
0.00348 0.0140 0.0650 0.00825
Pr 4 + (converted from Pr 3+) 0.860 1,24 -- 2,59 1.03 11,1
250
-~,5 N
0
50
100
150
200
r
2S0
300
(K)
Fig. I. Temperature dependence of the inverse magnetic susceptibility for PrBa2Cu3Oy and PrScl-~Mg.,O3. From upper side, PrBa2Cu3Oy (dotted line), x = 0.2, 0.15, 0.1, 0.05 and 0 (solid lines), respectively. The curves for x = 0 and 0.05 coincide with each other.
are o b t a i n e d from those of the P r 3 + ion. They are s h o w n in the third column. The values in the second c o l u m n agree in sign a n d the order of m a g n i t u d e with those in the third column. This suggests that P r 3+ a n d P r 4+ ions are on the same site, namely, the A site. 2. BaPrl-:~BixO3. In the BaPrx-xBixO3 system, only one intermediate phase BaPr0 sBi0.503 exists, in which the ordered a r r a n g e m e n t of P r a n d Bi ions on the B site is revealed by the superstructure line (0 l 1) in the X-ray diffraction pattern. The m a g n e t i c susceptibility of BaPrO3 which corresponds to Z of P r 4+ on the B site shows an antiferromagnetic ordering below 11 K, which agrees with the previous d a t a [3-6]. T h e magnetic susceptibility of BaPro.sBio.503 c o r r e s p o n d s to P r 3 + ions in an ordered a r r a n g e m e n t with Bi s + ion o n the B site. T h e magnetic susceptibility of P r 3+ a n d P r a+ ions in the B site are m u c h smaller t h a n those in the A site, reflecting the strong C E F at the B site. The magnetism of PrBa2Cu3Oy was previously examined by numerical calculation [7]. The magnetism of PrBa2Cu30>, is similar to that of P r 3 + ion at the A site of perovskite, where a small a m o u n t of P r 4 + ion is introduced (Fig. 1). The 4f energy level of P r ion a n d the energy of p b a n d of the CuO2 plane lie close with each other in PrBa2Cu30>. and the hybridization of 4f orbital a n d the O2p~ orbital of the CuO2 plane is expected. Therefore we suggest that the w f hybridization results in the ~ T behavior similar to that of P r ¢+ mixing. A part of this study was s u p p o r t e d by a G r a n t - i n - A i d for Scientific Research on Priority Areas 'New Development of Rare E a r t h C o m p l e x ' No. 08220262 from the Ministry of Education, Science a n d Culture, Japan.
References 400
....
[ ....
i ....
....
I
i
....
i , , , ,
350
-
Pr4÷ (expenmemal} .
300 250
I'r~" (
c
a
l
c
~
.2. 2~ 150
a< 11~ 50 $0
100
150
i'
200
250
300
(K)
Fig. 2. Temperature dependence of the inverse magnetic susceptibility, of molar Pr 3+ and Pr 4+ estimated from experimental values (solid lines) and calculated ones (dotted lines).
[1] H.B. Radousky, J. Mater. Res. 7 (1992) 1917. [2] A. Kebede, C.S. Jee, J. Schwegler, J.E. Crow, T. Mihalisin, G.H. Myer, R.E. Salomon, P. Schlottmann, M.V. Kuric, S.H. Bloom, R.P. Guertin, Phys. Rev. B 40 (1989) 4453. [3] M. Bickel, G.L. Goodman, L. Soderholm, J. Solid State Chem. 76 (1988) 178. [4] B. Lippold, J. Herrmann, U.-C. Boehnke, H. Boerner, J. Horn, H.-C. Semmelhack, M. Wurlitzer, Solid State Commun. 79 (1991) 487. [5] G. Cao, T. Yuen, P. Permambuco-Wise, J.E. Crow, J.W. O'Reilly, M.V. Kuric, R.P. Guertin, N. Rosov, J.W. Lynn, J. Appl. Phys. 70 (1991) 6332. [6] J.B. Bulman, M.V. Kuric, R.P. Guertin, S. Foner, E.J. McNiff Jr., G. Cao, J. O'Riely, J.E. Crow, P.P. Wise, T. Yuen, J. Appl. Phys. 69 (1991) 4874. [7] Y. Takano, S. Yokoyama, K. Kanno, K. Sekizawa, Physica C 252 (1995) 61.