Magneto-optical studies of the uniform critical state in bulk MgB2

We present a detailed magneto-optical investigation of the magnetic flux penetration in polycrystalline MgB2 slabs made by direct reaction of B and Mg. Our results unambiguously indicate a uniform, Bean critical state magnetization behavior with almost no electromagnetic granularity. From the measured magnetic flux profiles we were able to extract the temperature dependence of the critical current density Jc(T). The Jc(T) value reaches 1.8x10^5 A/cm2 at 10K and 0.12T, in good agreement with global magnetization measurements.