Magnetic properties of polycrystalline Ba0.5K0.5BiO3

The temperature and magnetic-field dependence of the magnetization in Ba0.5K0.5BiO3 samples have been measured in different temperature ranges in order to study the magnetic-field penetration depth L(T), the thermodynamic critical field Hc(T), and the critical fields Hc1(T) and Hc2(T). The L determined from the powder magnetization data is 803 at zero temperature. The Hc2 derived from the resistivity measurement is 15.4 T at zero temperature. This corresponds to a coherence length of (0)=43.3. The Hc estimated from the magnetization curve is 0.25 T at zero temperature. Hc1, Hc2, and Hc are discussed in the framework of Ginzburg-Landau theory.