A detailed magneto-optical investigation was made of the magnetic flux penetration into polycrystalline slabs made via the direct reaction of B and Mg. The results unambiguously indicated a uniform Bean critical state magnetization behavior, with almost no electromagnetic granularity. From the measured magnetic flux profiles, it was possible to extract the temperature dependence of JC. The JC(T) value reached 1.8 x 105A/cm2 at 10K and 0.12T; in good agreement with global magnetization measurements.

Magneto-Optical Studies of the Uniform Critical State in Bulk MgB2. A.A.Polyanskii, A.Gurevich, J.Jiang, D.C.Larbalestier, S.L.Budko, D.K.Finnemore, G.Lapertot, P.C.Canfield: Superconductor Science and Technology, 2001, 14, 811-5