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We report on the preparation of dense monofilamentary MgB 2 /Ni and MgB 2 /Fe tapes with high critical current densities. In annealed MgB 2 /Ni tapes, we obtained transport critical current densities as high as 2.3 × 10 5 A/cm 2 at 4.2 K and 1.5 T, and for MgB 2 /Fe tapes 10 4 A/cm 2 at 4.2 K and 6.5 T. To the best of our knowledge, these are the highest transport j c values at 4.2 K reported for MgB 2 based tapes so far. An extrapolation to zero field of the MgB 2 /Fe data gives a critical current value of ~ 1 MA/cm 2 , corresponding to an critical current value well above 1000 A. The high j c values obtained after annealing are a consequence of sintering densification and grain reconnection. Fe does not react with MgB 2 and is thus an excellent sheath material candidate for tapes with self-field j c values at 4.2 K in excess of 1 MA/cm 2 .

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The low temperature specific heat of a high purity YBa 2 Cu 3 O 7.00 single crystal grown in a BaZrO 3 crucible is measured from 1.2 to 10 K in magnetic fields from 0 to 14 T. The anisotropic component of the excess specific heat due to field,

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