Berg, van den, J.

Brom, H.B.

Hulstman, R.

Jol, J.C.

Kramer, G.J.

Pronk, B.

English

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89Y NMR as probe for the spin dynamics in the Cu(2)O-planes

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 89Y NMR as probe for the spin dynamics in the Cu(2)O-planesCitation for published version (APA):Brom, H. B., Kramer, G. J., Berg, van den, J., Pronk, B., Jol, J. C., & Hulstman, R. (1989). 89Y NMR as probe forthe spin dynamics in the Cu(2)O-planes. Synthetic Metals, 29(2-3), F553-F555. https://doi.org/10.1016/0379-6779(89)90950-8DOI:10.1016/0379-6779(89)90950-8Document status and date:Published: 01/01/1989Document Version:Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 16. Nov. 2023Synthetic Metals, 29 (1989) F553-F555 F553 sgy NMR AS PROBE FOR THE SPIN DYNAMICS IN THE Cu(2)O-PLANES H.B. BROM, G.J. KRAMER, J. VAN DEN BERG, B. PRONK, J.C. JOL and R. HULSTMAN Kamerlingh Onnes Laboratorium, Leiden University, P.O. Box 9506, 2300 RA Leiden, The Netherlands ABSTRACT The sgy nuclear relaxation rates in the orthorhombie 90 K superconducting and the tetragonal semiconducting modification of YBa2CusOT-6 are almost similar. These results are correlated to Y line shift data  and Cu- NMR results. A relaxation process via magnetic excitations in active regions of the Cn(2)O planes allows a consistent picture. INTRODUCTION Resonance is usually a suitable tool to probe the charge and spin dynamics in conducting and/or  magnetic systems. In YBa~CusO~_s (YBCO), ESR is only of limited use, because of the absence of a signal in single crystals of the 90 K superconductor [1]. In this contri- bution we will discuss our Y-relaxation measurements obtained in the orthorhombic 90 K superconducting (O-YBCO) and the tetragonal semiconducting (T-YBCO) modification of YBCO [2]. Recently also Y-line shift data  have become available [31. Furthermore, since the univocal assignment of the NMR quadupolar lines to the Cu sites far reaching conclusions were possible [4,5,6] about the oxygen vacancies and their relation to the resonance spectra. We will try to give a consistent explanation of these various results. It will be shown that  our da ta  corroborate the suggestion of Warren et al. [6] of the existence of active and inactive regions in the Cu(2)O- planes, and further that  it is the spin dynamics rather that  the conduction electrons, that  is probed via the Y relaxation rate. 0379-6779/89/$3.50 © Elsevier Sequoia/Printed in The Netherlands F554 EXPERIMENTAL In our mainly home-built NMR set-up the Y-NMR data  were taken at a frequency of 9.8 MI-Iz by using a comb of ~r/2 pulses followed by a reading pulse of ~r/2. A decay time of 200-300/~s was allowed to suppress the effect of 'electronic noise' in the signal without too severe loss of sensitivity - for T-YBCO a decay time of about 0.4 ms compared to 1 ms for O-YBCO was typical. The magnetic field was provided by an Oxford Instruments 4.7 T NMR-magnet with a room temperature bore of 5 cm, allowing insert of a flow cryostat. Temperatures were measured with a Pt-resistor and Au-chromel thermocouple. RESULTS AND DISCUSSION The main result of our Y-NMR data  is that  above 100 K there is only a slight decrease in relaxation rate [2,7], if one goes from the 90 K superconducting compound to the tetragonai non-superconducting material. The linear temperature dependence then suggests coupling to spin excitations with Fermi-Dirac statistics, like e.g. ordinary conduction electrons or holes or spinons, as proposed in the Resonant Valence Bond (RVB) model [8]. In the first interpretation the large difference in conductance between the g0 K superconductor and the tetragonai semiconductor (we measured a factor of more than 10 s) requires additional modelling. The accurate line shift measurements of Alloul et al. [3] show apart  from the dominance of the chemical shift, a gradual decrease of the superposed Knight shift with increasing 6-value. For 6 > 0.6 only the chemical shift is observed: the 6-value of a quenched sample as ours is estimated to be around 6 = 0.T. If the same conduction electrons that  are responsible for the Knight shift determine the relaxation, a decrease in relaxation rate of a few orders of magnitude had to be observed between the 2 samples - in contrast with experiment. If magnetic excitations are the source of the relaxation rate, there is no such contradiction. Because of the fast fluctuations of the spin direction it is the averaged spin component which determines the resultant shift: there is no such direct relation between shift and relaxation rate as for a Korringa process. The Y-NMR data  of Warren et al. [6] in the 60 K superconductor confirm our finding that  the Y relaxation rate is only modestly affected by oxygen loss. Also on basis of the Cu-NMR data, they conclude that  there is still ample though possibly quite inhomogeneous dynamical character at a sizeable fraction of planar sites. In such a picture it might be assumed that  mainly those Y nuclei that  are coupled to the excitations in the active regions are observed. Indeed a typical t ime constant for Y spin diffusion in YBCO will be a few hundred seconds [7], which is longer than the observed nuclear relaxation rate. If the spin dynamics in active regions hardly changes under variation of 6 (6 < 0.7), then the same holds for the observed Y relaxation rate (the Y-sites in non-active regions are unobservable). F555 In conclusion we have shown that a consistent interpretation of the available NMR data is possible if the observed Y nuclei are relaxed by magnetic spin excitations on 'active'regions in the Cu(2) planes. More precise data about these active regions are required to draw further conclusions. ACKNOWLEDGEMENTS This work is part of the research program of the Leiden Materials Science Centre (Werk- groep Fundamenteel Materialen Onderzoek) and is supported by the Foundation for the Fun- damental Research on Matter (FOM), which is sponsored by the Netherlands Organization for the advancement of Pure Research (ZWO). REFERENCES [1] J. Albino O. de Aguiar, A.A. Menovsky, J. van den Berg and H.B. Brom, J. Phys. C, 21 (1988) L237. [2] H.B. Brom, G.J. Kramer, J. van den Berg and J.C. Jol, Phys. Rev. B RC, in print. [3] H. Alloul, P. Mendels, G. Collin and P. Monod, preprint 1988. [4] See e.g. the proceedings of the HTS2M Interlaken, Febr. 29-March 4 (1988), to be pub- lished in Physica C, 153 [5] R.E. Walstedt, W.W. Warren, R. Tycko, R.F. Bell, G.F. Brennert, R.J. Cava, L. Schneemeyer and J. Waszcak, preprint 1988. [6] W.W. Warren, R.E. Walstedt, G.F. Brennert, R.J. Cava, B. Batlogg and L.W. Rupp, preprint 1988. [7] J.T. Markert, T.W. Noh, S.E. Ruesek and R.M. Cotts, Solid State Commun., 63 (1987) 847. [8] Z. Zou and P.W. Anderson, Phys. Rev. B, 37 (1988) 627. 

89Y NMR as probe for the spin dynamics in the Cu(2)O-planes

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