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

We present a detailed magneto-optical investigation of the magnetic flux pe netration in polycrystalline MgB2 slabs made by direct reaction of B and Mg . Our results unambiguously indicate a uniform, Bean critical state magneti zation behaviour with almost no electromagnetic granularity. From the measu red magnetic flux profiles we were able to extract the temperature dependen ce of the critical current density J(c)(T). The J(c)(T) value reaches 1.8 x 10(5) A cm(-2) at 10 K and 0.12 T, in good agreement with global magnetiza tion measurements.