Magnetic-field dependence of the reversible axial-strain effect in Y-Ba-Cu-O coated conductors

The critical-current density J/sub c/ of an yttrium-barium-copper-oxide (YBCO) coated conductor deposited on a biaxially-textured Ni-5at.%W substrate was measured at 76.5 K as a function of axial tensile strain /spl epsiv/ and magnetic field B applied parallel to the YBCO (a,b) plane. Reversibility of J/sub c/ with strain was observed up to /spl epsiv//spl sime/0.6% over the entire field range studied (from 0.05 to 16.5 T), which confirms the existence of an intrinsic strain effect in YBCO coated conductors. J/sub c/ vs. /spl epsiv/ depends strongly on magnetic field. The decrease of J/sub c/(/spl epsiv/) grows systematically with magnetic field above 2-3 T, and, unexpectedly, the reverse happens below 2 T as this decrease shrinks with increasing field. The pinning force density F/sub p/=J/sub c//spl times/B scaled with field for all values of strain applied, which shows that F/sub p/ can be written as K(T,/spl epsiv/)b/sup p/(1-b)/sup q/, where p and q are constants, K is a function of temperature and strain, b=B/B/sub c2//sup */ is the reduced magnetic field, and B/sub c2//sup */ is the effective upper critical field at which F/sub p/(B) extrapolates to zero.