Large magneto-resistance of high-T C superconductor based composites to low magnetic fields at the liquid nitrogen temperature D.A. Balaev a, * , K.A. Shaihutdinov a , S.I. Popkov a,b , D.M. Gokhfeld a,b , M.I. Petrov a a Kirensky Intitute of Physics, Akademgorodok, Krasnoyarsk 660036, Russia b Reshetnev Siberian State Aerospace University, Krasnoyarsk 660014, Russia Abstract Themagneto-resistiveeffectinbulk123YBCO+CuOandYBCO+NormalmetalBaPbO 3 composites prepared by fastbackingtechniquehasbeenstudied.Thecompositesexhibitbroadeningofresistivetransitioninlowmagneticfields (lessthan200Oe)forawidetemperaturerange.Experimentaldependencesofresistivityversusmagneticfieldatvarious transportcurrentdensitiesarepresentedanddiscussed.TheHTSCbasedcompositesexhibitamuchhighersensitivity toweakmagneticfieldsatliquidnitrogentemperature,ascomparedtothatforthe‘‘pure’’HTSCceramics.Thiseffect is attractive for possible practical applications and may be used in magnetic field sensor devices. Ó 2004 Elsevier B.V. All rights reserved. Keywords: HTSC; Magnetic field sensors; Magneto-resistance 1. Introduction In Ref. [1] the preliminary results of study of mag- neto-resistive effect in composites YBCO+CuO and YBCO+metaloxideBaPbO 3 are presented. Broadening of resistive transition of the composites under the influ- ence of weak magnetic fields (less than 200 Oe) is ob- servedforatemperaturerange 50–90K[1]incontrast to‘‘pure’’polycrystallineHTSCswherethistemperature interval is very narrow, typically amounting to several degrees (85–90 K for the yttrium HTSC [2]). In this re- port we present the results of detail study of magnetic field dependences of resistivity qðH Þ ofthecomposites. 2. Experimental Composite samples with 70–85 vol.% of Y 3=4 Lu 1=4 Ba 2 Cu 3 O 7 (YBCO) and 30–15 vol.% CuO or 15 vol.% BaPbO 3 were prepared by fast backing tech- nique described in [3,4]. Hereafter we denote composite samples as YBCO+ V CuO and YBCO+ V BaPbO 3 where V is vol. content of CuO and BaPbO 3 respec- tively,thevol.contentofY 3=4 Lu 1=4 Ba 2 Cu 3 O 7 is100  V . The qðH Þ dependences have been measured by stan- dard four-probe technique. The samples have been cooled in zero magnetic field (the Earth magnetic field has not been screened). The transport current was per- pendicular to magnetic field direction. The value of critical current density j C was determined from the ini- tial part of current–voltage characteristic using the standard criterion 1 lV/cm. 3. Results and discussion The character of qðH Þ dependence of composites is found to depend on the relationship between bias cur- rent j and critical current j C . If current j islessthanits critical value, j=j C < 1 (case 1), there is a part of qðH Þ where q 6 10 6 X cm, see Fig. 1a and c. Starting from some threshold field H C nonlinear qðH Þ dependence * Corresponding author. E-mail address: smp@iph.krasn.ru (D.A. Balaev). 0921-4534/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2004.03.173 Physica C 408–410 (2004) 943–944 www.elsevier.com/locate/physc