Ž . Physica C 330 2000 181–190 www.elsevier.nlrlocaterphysc Zn doping of YBa Cu O in melt textured materials: peak effect 2 3 7 and high trapped fields G. Krabbes a, ) , G. Fuchs a , P. Schatzle a , S. Gruß a , J.W. Park b , F. Hardinghaus b , ¨ G. Stover a , R. Hayn a , S.-L. Drechsler a , T. Fahr a ¨ a IFW, Institute of Solid State and Materials Research Dresden, POB 270016, 01171 Dresden, Germany b SolÕay Barium Strontium, 30002 HannoÕer, Germany Received 15 November 1999; accepted 30 November 1999 Abstract Ž . The previously introduced modified melt crystallization process MMCP has been applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk. A field induced pinning was indicated by a well pronounced peak of the critical current density j in the j c c Ž . vs. H relationship for the maximal oxidized overdoped material containing Zn, whereas pure overdoped YBCO shows no peak effect. The peak effect for Zn-doped YBCO appearing for T s77 K at a relatively high field of about 3 T can be attributed to pair breaking by locally induced magnetic moments due to in plane Zn for Cu substitution. Besides high quality of the bulk YBCO, the peak effect is the reason for the trapped field as large as 1.12 T at 77 K in the cylinder of only 25 mm in diameter. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Peak effect; Magnetization; Pinning force; Substitution effects; Bulk superconductors 1. Introduction The response of a superconductor to magnetic field is an important feature especially for the REBa Cu O representatives among the high-T 2 3 7yd c superconductors. Applications have been suggested which are based on the peculiarities of the magneti- zation loop in these hard superconductors and on the forces between the bulk HTSC and an external field, i.e., in magnetic bearings, linear frictionless transport systems, permanent magnets, flywheels for energy ) Corresponding author. Tel.: q 49-351-4659-410; fax: q 49- 351-4659-480. Ž . E-mail address: g.krabbes@ifw-dresden.de G. Krabbes . storage and medium-sized electromotors. Any tech- nical application will rely on the availability of efficient materials with high values of j , the rema- c Ž . nent induction B ‘‘trapped field’’ , high levitation 0 forces and stiffness of the superconductor in dy- namic interaction with the applied field. The latter is immediately related to the intragrain j whereas the c appearance of large trapped fields is determined by Ž the product j = d with d as the diameter of the c . supercurrent loop . Thus, modifications of process- ing have been applied to improve the properties of the bulk materials, the up to now most important Ž . representative of which is YBa Cu O Y-123 . 2 3 7yd Typically, the bulk is a composite consisting of Ž . Y-123 and fine particles of Y BaCuO Y-211 , 2 5 0921-4534r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0921-4534 99 00616-4