Cryst. Res. Technol. 44, No. 9, 930 – 936 (2009) / DOI 10.1002/crat.200900306 © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Magneto-transport properties of polycrystalline YBa 2 (Cu 1-x M x ) 3 O 7-δ (M = B and Mn) B. A. Albiss* 1,2 , I. M. Obaidat 3 , M. Gharaibeh 2 , W. Hatamleh 2 , S. A. Barhoum 2 , and M. K. Hasan 2 1 Physikalisches Institut III, Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, 91058 Erlangen, Germany 2 Superconductivity and Magnetic Measurements Laboratory, Physics Department, Jordan University of Science and Technology, 22110 Irbid, Jordan 3 Department of Physics, United Arab Emirates University, Al-Ain 17551, United Arab Emirates Received 21 May 2009, revised 15 June 2009, accepted 1 July 2009 Published online 22 July 2009 Key words superconductor, chemical doping, vortex pinning, critical current density, grain boundaries. PACS 75.25.Qt, 74.72.Bk, 74.25.Ha The magnetic and transport properties of polycrystalline YBa 2 (Cu 1-x M x ) 3 O 7-δ (M = B and Mn) superconductor was investigated. Samples of YBa 2 (Cu 1-x B x ) 3 O 7-δ doped with several concentrations of boron B (x = 0.05 and 0.1) were investigated using magnetization measurements. A YBa 2 (Cu 1-x Mn x ) 3 O 7-δ sample doped with Mn with concentration of x = 0.02 was investigated using current-voltage (I-V) measurements. Our results on the YBa 2 (Cu 1-x B x ) 3 O 7-δ samples reveal a considerable increase in the hysterisis width of the magnetization, M versus the applied magnetic field H with increasing boron concentration. The lower critical field was also found to be enhanced by boron doping. The critical current density, J c was found to be significantly enhanced in the Mn-doped sample. The enhancement of J c was found to be more significant at the lower temperatures for all applied magnetic fields used (0 Oe, 300 Oe, and 500 Oe). Thus, chemical doping is suggested to enhance the vortex pinning forces in the YBCO samples. From the resistivity (R-T) measurements, chemical doping of the samples was found to have no significant effect on the critical temperature, T c . © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction High-temperature superconductors (HTSCs) in magnetic fields of strength higher than H c1 and smaller than H c2 are known to be in the mixed state, where magnetic field penetrates the superconductors in form of quantized magnetic vortices. When a transport current density, J is applied to HTSC in the mixed state it will produce a Lorentz force, F L on the vortices trying to move them. The Lorentz force is given by; F L = (1/c) J×Φ o where Φ o is the quantized magnetic flux per vortex. If the Lorentz force is not opposed by pinning forces, an electric field, E = (-1/c) B×v will be induced in the sample causing energy to be dissipated, were v is the velocity of vortices transverse direction to both J and B, and B is the applied magnetic field. Unfortunately, the pinning of vortices in HTSCs is fairly weak, especially at high temperatures [1]. The vortices can be effectively pinned by any structural inhomogeneities of the material. A lot of work has been done to increase the critical current density J c that can be sustained by these materials. Defects created in the HTSCs using several types of energetic radiations were found to be very successful in increasing the vortex pinning forces [2-5]. Other techniques have been used during the sample preparation by changing the heat treatment where good quality samples might be obtained to carry high currents [6,7]. Introducing nano-particles in bulk superconductors has been also used to increase the pinning forces [8,9] and thus to enhance J c . Although great progress has been ____________________ * Corresponding author: e-mail: borhan.albiss@physik.uni-erlangen.de