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Anomalous properties of PrBa2Cu3O7: a comment
PHYSICA
Physica B 176 (1992) 217-218 North-Holland
Anomalous properties of PrBa2Cu307: a comment E.V. S a m p a t h k u m a r a n Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay-400005, India
Received 2 August 1991 Considerable attention has been paid in the literature to understand the suppression of superconductivityand the large N6el temperature of the Pr sub-lattice in PrBa2CusO7. Here we brieflyrecall the superconductingand magnetic anomalies noted earlier in other Pr based systems due to the partial delocalisation of the Pr-4f orbital to show that the gross anomalous features observed for PrBa2Cu307 are not unique. After the breakthrough of the field of hightemperature superconductivity, the properties of the compound, PrBa2Cu30 7 (hereafter referred to as Pr123), arouse considerable excitement for mainly two reasons [1, 2]. Firstly, the superconducting transition temperature (To) of YB2Cu30 7 is not influenced significantly ( T c 90 K) by the replacement of Y by heavy rareearths, containing large effective moments; however, the compound Pr123 is not even a metal, even though the holes in the O2p band, thought to be responsible for superconductivity in other R B a 2 C u 3 0 7 (R = rare earth) compounds (R123), are present [3,4] in this compound. Secondly, the antiferromagnetic ordering temperature (TN) of the Pr sub-lattice is unusually large ( ~ 1 7 K ) than that known for any other heavy rare-earth member of this series with considerably higher magnetic moments. For the Gd analog, for example, the value of T N is ~2.2 K. These properties of Pr123 generated considerable activity and the interested readers are urged to see the publications cited in refs. [1-4]. (As this article is not aimed to review all the reports on Pr123, we refrain from citing the complete literature on this system.) These unexpected gross features of Pr123 led several groups to propose that Pr valency is close to four and this resulted in a debate on the valency of Pr in Pr123. However, there appears to be a consensus that the Pr-4f valence-band hybridization
strength is large and, in consistency with this idea, the electronic heat-capacity ( y ) is very large [5]. It may be pointed out that our initial work [6] was one of the first few reports to claim a strongly 4f-hybridized, trivalent Pr state in Pr123. Here we point out that both the properties of P r 1 2 3 - s u p p r e s s i o n of superconductivity and anomalous magnetism - as well as heavy-fermion behavior are not unique for this compound. Somewhat similar properties, though not all in a single system, have been reported in metals containing trivalent Pr and such findings have been ignored while interpreting the experimental resuits on Pr123 in the literature. With respect to superconductivity, it is known that Pr metal undergoes a localisation-delocalisation transition under a high pressure of about 230 kbar and, at this pressure, the depression of the superconducting transition temperature of La due to the presence of Pr impurities shows, a pronounced maximum in analogy to the familiar case of the Ce impurities in La at low pressure [7]; similar effects on the superconductivity of ZrB12, LaRu 2 and LaSn 3 [8-11] are caused by doped Pr impurities. With respect to the anomalous magnetism, we have highlighted [12] that the ternary Pr compounds, crystallizing in the ThCr2Si2-type structure [13], like PrCu2Si 2 ( T N ~ 2 1 K ) , PrCu2Ge 2 ( 1 6 K ) , PrNi2Si 2 ( 2 0 K ) , etc., order magnetically at temperatures that surpass the
0921-4526/92/$05.00 © 1992- Elsevier Science Publishers B.V. All rights reserved
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E.V. Sampathkumaran / Anomalous properties of PrBaeCu~O 7
value known for the corresponding Gd analog (15, 12, and 14 K respectively); the value of T N is otherwise the highest for the Gd case in the respective series, as expected. In all these Pr compounds, Pr ions are trivalent and an unusually large anisotropic 4f-hybridization has been proposed to be responsible for the anomalous magnetism [12]. It is also important to note that the compound PrCu2Si 2 appears to behave like a heavy-fermion as in the case of Pr123 [12]. All these reports point to the fact that one can expect anomalous magnetism and suppression of superconductivity even for trivalent Pr as long as the chemical surrounding is favorable for strong hybridization of the delocalised M-orbital. In other words, there is no need to invoke the idea of a valence change to explain the properties of Pr123. Finally, we take this opportunity to recall other manifestations of the partially extended character of Pr 4f orbital noted occassionally in a few chemical environments. Kondo-like behavior for Zr~ ,Pr, Br2 and PrSn 3 [8-11] as well as for Pr doped in very dilute limits in various metallic matrices like Pd [14], Ta, W, Os and Ir [15] has been reported. It appears [16] and PrNi 2 also exhibits an anomalously large value of y like PrCu_,Si, and there has been no serious attempt to investigate this aspect further. With respect to the spectrocopic data, double peaked structures in the 4f-derived valence-band photoemission spectra of binary Pr compounds, with a prominent feature near the Fermi level, typical of the anomalies in Ce compounds due to strong 4f hybridization, have been reported [17]. The spectroscopic features of PrO 2 have led to controversies on the valency of Pr similar to that of CeO~ [18]. These observations suggest that Pr systems depending upon the chemical environment exhibit all the anomalies characterizing the 4f radial extension in Ce systems. Thus, we emphasize that it is worthwhile to reactivate the investigations of Pr-containing materials in view of the current interest in Pr123.
References [1] 1. Das, E.V. Sampathkumaran, R. Vijayaraghavan, Y. Nakazawa and M. Ishikawa, Physica C 173 (1991) 331, and references therein.
[2] D.P. Norton, D.H. Lowndes, B.C. Sales, J.D. Budai, B.C. Chakoumakos and H.R. Kerchner, Phys. Rev. Lett. 66 (19911 1537, and references therein. [3] D.D. Sarma, P. Sen, R. Climino, C. Carbone, W. Gudat, E.V. Sampathkumaran and I. Das, Solid State Commun. 77 (1991) 377. [4] J. Fink, N. Nucker, H. Romberg, M. Alexander, M.B. Maple, J.J. Neumeier and J.W. Allen, Phys. Rev. B 42 (19901 4823. [5] W.-H. Li, J.W. Lynn, S. Skanthakumar, T,W. Clinton, A. Kebede, C.-S. Jee, J.E. Crow and T. Mihalisin, Phys. Rev. B 4(1 (1989) 5300. [6] E.V. Sampathkumaran, A. Suzuki, K. Kohn, T. Shibuya, A. Tohdake and M. Ishikawa, Jpn. J. Appl. Phys. 27 (1988) 584, L792. N. Ikeda, K. Kohn, E.V. Sampathkumaran and R. Vijayaraghavan, Solid State Commun. 68 (1988) 51. I7] J. Wittig, in: Physics of Solids under Pressure, eds. J.S. Schilling and R.N. Shelton (North-Holland, Amsterdam, 1981) p. 283, J. Wittig, Phys. Rev. Lett. 46 (19811 1431. [8] Z. Fisk and B.T. Matthias, Science 165 (19691 279. [9] P. Weidner, A. Freimuth, K. Keulerz, B. Politt, B. Roden, J. Rohler and D. Wohlleben, J. Magn. Magn. Mater. 47 & 48 (1985) 599. A. Slebarski, D. Wohlleben and P. Weidner, Z. Phys. B 61 (1985) 177. [101 B. Hillenbrand and M. Wilhelm, Phys. Lett. A 33 (1971)) 61. [11] P. Lethuillier and P. Haen, Phys. Rev. Lett. 35 (1975) 1391. See, for review, M.B. Maple, L.E. DeLong and B.C. Sales, in: Handbook on the Physics and Chemistry of Rare-earths, Vol. 1, eds. K.A. Gschneidner, Jr and L. Eyring (North-Holland, Amsterdam, 1978) p. 797. [12] E.V. Sampathkumaran, I. Das and R. Vijayaraghavan, Proceedings of the Solid State Symposium, Bombay, India, January 1991, Phys. Rev. B 33C (1991) 260. E.V. Sampathkumaran, I. Das, R. Vijayaraghavan, K. Hirota and M. Ishikawa, Solid State Commun. 78 (1991) 971. [13] A. Szytula and J. Leciejewicz, in: Handbook on the Physics and Chemistrty of Rare Earths, Vol. 12, eds. K.A. Gschneidner, Jr and L. Eyring (North-Holland, Amsterdam, 1989)p. 133. [14] U. Walter and A. Slebarski, Z. Phys. B 76 (19891 507. [15] L. Buermann, H.J. Barth, K.H. Beidermann, M. Luszik-Bhadra and D. Riegel, Phys. Rev. Lett. 56 (1986) 492. [16] H. Mori, T. Satoh, T. Fujita and T. Ohtsuka, J. Low Temp. Phys. 49 (1982) 397. [17] G. Kalkowski, E.V. Sampathkumaran, C. Laubschat, M. Domke and G. Kaindl, Solid State Commun. 55 (1985) 977. R.D. Parks, S. Raaen, M.L. de Boer, Y.S. Chang and G.P. Williams, Phys. Rev. Lett. 52 (1984) 2176. M.D. Nunez-Regueiro and M. Avignon, Phys. Rev. Lett. 55 (1985) 615. [18] H. Ogasawara, A. Kotani, K. Okada and B.T. Thole, Phys. Rev. B 43 (1991) 854.
Physica B 176 (1992) 217-218 North-Holland
Anomalous properties of PrBa2Cu307: a comment E.V. S a m p a t h k u m a r a n Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay-400005, India
Received 2 August 1991 Considerable attention has been paid in the literature to understand the suppression of superconductivityand the large N6el temperature of the Pr sub-lattice in PrBa2CusO7. Here we brieflyrecall the superconductingand magnetic anomalies noted earlier in other Pr based systems due to the partial delocalisation of the Pr-4f orbital to show that the gross anomalous features observed for PrBa2Cu307 are not unique. After the breakthrough of the field of hightemperature superconductivity, the properties of the compound, PrBa2Cu30 7 (hereafter referred to as Pr123), arouse considerable excitement for mainly two reasons [1, 2]. Firstly, the superconducting transition temperature (To) of YB2Cu30 7 is not influenced significantly ( T c 90 K) by the replacement of Y by heavy rareearths, containing large effective moments; however, the compound Pr123 is not even a metal, even though the holes in the O2p band, thought to be responsible for superconductivity in other R B a 2 C u 3 0 7 (R = rare earth) compounds (R123), are present [3,4] in this compound. Secondly, the antiferromagnetic ordering temperature (TN) of the Pr sub-lattice is unusually large ( ~ 1 7 K ) than that known for any other heavy rare-earth member of this series with considerably higher magnetic moments. For the Gd analog, for example, the value of T N is ~2.2 K. These properties of Pr123 generated considerable activity and the interested readers are urged to see the publications cited in refs. [1-4]. (As this article is not aimed to review all the reports on Pr123, we refrain from citing the complete literature on this system.) These unexpected gross features of Pr123 led several groups to propose that Pr valency is close to four and this resulted in a debate on the valency of Pr in Pr123. However, there appears to be a consensus that the Pr-4f valence-band hybridization
strength is large and, in consistency with this idea, the electronic heat-capacity ( y ) is very large [5]. It may be pointed out that our initial work [6] was one of the first few reports to claim a strongly 4f-hybridized, trivalent Pr state in Pr123. Here we point out that both the properties of P r 1 2 3 - s u p p r e s s i o n of superconductivity and anomalous magnetism - as well as heavy-fermion behavior are not unique for this compound. Somewhat similar properties, though not all in a single system, have been reported in metals containing trivalent Pr and such findings have been ignored while interpreting the experimental resuits on Pr123 in the literature. With respect to superconductivity, it is known that Pr metal undergoes a localisation-delocalisation transition under a high pressure of about 230 kbar and, at this pressure, the depression of the superconducting transition temperature of La due to the presence of Pr impurities shows, a pronounced maximum in analogy to the familiar case of the Ce impurities in La at low pressure [7]; similar effects on the superconductivity of ZrB12, LaRu 2 and LaSn 3 [8-11] are caused by doped Pr impurities. With respect to the anomalous magnetism, we have highlighted [12] that the ternary Pr compounds, crystallizing in the ThCr2Si2-type structure [13], like PrCu2Si 2 ( T N ~ 2 1 K ) , PrCu2Ge 2 ( 1 6 K ) , PrNi2Si 2 ( 2 0 K ) , etc., order magnetically at temperatures that surpass the
0921-4526/92/$05.00 © 1992- Elsevier Science Publishers B.V. All rights reserved
218
E.V. Sampathkumaran / Anomalous properties of PrBaeCu~O 7
value known for the corresponding Gd analog (15, 12, and 14 K respectively); the value of T N is otherwise the highest for the Gd case in the respective series, as expected. In all these Pr compounds, Pr ions are trivalent and an unusually large anisotropic 4f-hybridization has been proposed to be responsible for the anomalous magnetism [12]. It is also important to note that the compound PrCu2Si 2 appears to behave like a heavy-fermion as in the case of Pr123 [12]. All these reports point to the fact that one can expect anomalous magnetism and suppression of superconductivity even for trivalent Pr as long as the chemical surrounding is favorable for strong hybridization of the delocalised M-orbital. In other words, there is no need to invoke the idea of a valence change to explain the properties of Pr123. Finally, we take this opportunity to recall other manifestations of the partially extended character of Pr 4f orbital noted occassionally in a few chemical environments. Kondo-like behavior for Zr~ ,Pr, Br2 and PrSn 3 [8-11] as well as for Pr doped in very dilute limits in various metallic matrices like Pd [14], Ta, W, Os and Ir [15] has been reported. It appears [16] and PrNi 2 also exhibits an anomalously large value of y like PrCu_,Si, and there has been no serious attempt to investigate this aspect further. With respect to the spectrocopic data, double peaked structures in the 4f-derived valence-band photoemission spectra of binary Pr compounds, with a prominent feature near the Fermi level, typical of the anomalies in Ce compounds due to strong 4f hybridization, have been reported [17]. The spectroscopic features of PrO 2 have led to controversies on the valency of Pr similar to that of CeO~ [18]. These observations suggest that Pr systems depending upon the chemical environment exhibit all the anomalies characterizing the 4f radial extension in Ce systems. Thus, we emphasize that it is worthwhile to reactivate the investigations of Pr-containing materials in view of the current interest in Pr123.
References [1] 1. Das, E.V. Sampathkumaran, R. Vijayaraghavan, Y. Nakazawa and M. Ishikawa, Physica C 173 (1991) 331, and references therein.
[2] D.P. Norton, D.H. Lowndes, B.C. Sales, J.D. Budai, B.C. Chakoumakos and H.R. Kerchner, Phys. Rev. Lett. 66 (19911 1537, and references therein. [3] D.D. Sarma, P. Sen, R. Climino, C. Carbone, W. Gudat, E.V. Sampathkumaran and I. Das, Solid State Commun. 77 (1991) 377. [4] J. Fink, N. Nucker, H. Romberg, M. Alexander, M.B. Maple, J.J. Neumeier and J.W. Allen, Phys. Rev. B 42 (19901 4823. [5] W.-H. Li, J.W. Lynn, S. Skanthakumar, T,W. Clinton, A. Kebede, C.-S. Jee, J.E. Crow and T. Mihalisin, Phys. Rev. B 4(1 (1989) 5300. [6] E.V. Sampathkumaran, A. Suzuki, K. Kohn, T. Shibuya, A. Tohdake and M. Ishikawa, Jpn. J. Appl. Phys. 27 (1988) 584, L792. N. Ikeda, K. Kohn, E.V. Sampathkumaran and R. Vijayaraghavan, Solid State Commun. 68 (1988) 51. I7] J. Wittig, in: Physics of Solids under Pressure, eds. J.S. Schilling and R.N. Shelton (North-Holland, Amsterdam, 1981) p. 283, J. Wittig, Phys. Rev. Lett. 46 (19811 1431. [8] Z. Fisk and B.T. Matthias, Science 165 (19691 279. [9] P. Weidner, A. Freimuth, K. Keulerz, B. Politt, B. Roden, J. Rohler and D. Wohlleben, J. Magn. Magn. Mater. 47 & 48 (1985) 599. A. Slebarski, D. Wohlleben and P. Weidner, Z. Phys. B 61 (1985) 177. [101 B. Hillenbrand and M. Wilhelm, Phys. Lett. A 33 (1971)) 61. [11] P. Lethuillier and P. Haen, Phys. Rev. Lett. 35 (1975) 1391. See, for review, M.B. Maple, L.E. DeLong and B.C. Sales, in: Handbook on the Physics and Chemistry of Rare-earths, Vol. 1, eds. K.A. Gschneidner, Jr and L. Eyring (North-Holland, Amsterdam, 1978) p. 797. [12] E.V. Sampathkumaran, I. Das and R. Vijayaraghavan, Proceedings of the Solid State Symposium, Bombay, India, January 1991, Phys. Rev. B 33C (1991) 260. E.V. Sampathkumaran, I. Das, R. Vijayaraghavan, K. Hirota and M. Ishikawa, Solid State Commun. 78 (1991) 971. [13] A. Szytula and J. Leciejewicz, in: Handbook on the Physics and Chemistrty of Rare Earths, Vol. 12, eds. K.A. Gschneidner, Jr and L. Eyring (North-Holland, Amsterdam, 1989)p. 133. [14] U. Walter and A. Slebarski, Z. Phys. B 76 (19891 507. [15] L. Buermann, H.J. Barth, K.H. Beidermann, M. Luszik-Bhadra and D. Riegel, Phys. Rev. Lett. 56 (1986) 492. [16] H. Mori, T. Satoh, T. Fujita and T. Ohtsuka, J. Low Temp. Phys. 49 (1982) 397. [17] G. Kalkowski, E.V. Sampathkumaran, C. Laubschat, M. Domke and G. Kaindl, Solid State Commun. 55 (1985) 977. R.D. Parks, S. Raaen, M.L. de Boer, Y.S. Chang and G.P. Williams, Phys. Rev. Lett. 52 (1984) 2176. M.D. Nunez-Regueiro and M. Avignon, Phys. Rev. Lett. 55 (1985) 615. [18] H. Ogasawara, A. Kotani, K. Okada and B.T. Thole, Phys. Rev. B 43 (1991) 854.