Magnetization measurements of 5 μm Ba0.6K0.4BiO3 crystals

This paper reports on magnetization measurements on cubic Ba0.6K0.4BiO3 crystals, approximately 5 μm in radius, obtained using a recently-developed electrodynamic force balance technique. The onset of flux entry in an external field H is marked by a pronounced deviation from a linear magnetization at a critical field H*cl together with a noticeable reorientation of the crystal near H = 0, a reorientation caused by the field-induced torque on the remanent moment. The dependence of H*cl on temperature is linear over the temperature range 7K ≤ T ≤ 30 K with a slope approximately a factor of three higher than published values. These higher values of H*cl imply either intrinsically cleaner material with a reduced Ginzburg-Landau parameter κ or higher surface critical fields. These results suggest that the intrinsic properties of high-Tc superconductors may be more accurately reflected in small crystals which are more likely to be of higher quality than large crystals