The first critical fields and critical currents of the monodomain TmBa2Cu3Ox superconducting single crystals

The critical field HcI of the monodomain TmBa2Cu3Ox superconducting single crystals are measured along all three crystallographic axes. These data determine in the logarithmic approximation the ratio of the penetration depths: λa: λb:λc = I:I. 7:4.4. For H parallel c the dependence of HcI on temperature is a linear function with the slope of about 22 Oe/K for T > IO K. Angular dependences of the Meissner magnetic susceptibility and HcI in the (bc)-plane were studied. The expression derived in the ellipsoid approximation shows a good agreement with these data. Temperature dependences of the critical current jc(T) are also measured. Different types of single crystals are used, including the monodomain crystal. For all samples the jc(T) curves follow the exponential dependence jc(T) = jc (O) exp(-T/T0) with the jc(O) value of about (2-3) IO6 A/cm2. The jc(O) independence on the density of domain walls suggests a weak pinning by a twinning plane