Angular dependence of the bulk nucleation field Hc2 of aligned MgB2 crystallites - art. no. 144517

The angular dependence of the bulk nucleation field of a sample made of ali gned MgB2 crystallites was obtained using dc magnetization and ac susceptib ility measurements. A good fitting of the data by the three-dimensional ani sotropic Ginzburg-Landau theory attests to the bulk nature of the critical field H-c2. We found a mass anisotropy ratio epsilon2 approximate to0.39 th at implies an anisotropy of the Fermi velocity, with a ratio of 1.6 between the in-plane and perpendicular directions, if an isotropic gap energy is a ssumed. For an s-wave anisotropic gap this ratio could increase to 2.5. Bes ides the fundamental implications of this result, it also implies the use o f texturization techniques to optimize the critical current in wires and ot her polycrystalline forms of MgB2.