Anisotropy in MgB2

Abstract

The first direct measurement of an anisotropic superconducting property in MgB2 was achieved for the bulk nucleation field Hc2, in a sample of aligned crystallites. It was found a ratio γ(T ) = H ab c2 /H c c2 = 1.6 − 1.9, for T varying from 32 K to 26K, between H applied parallel to the ab plane, and along the c direction. The anisotropy of the induced critical current density was evaluated through the Bean model to be J ab c /J c c ≈ 1.5. We present here a brief review of these studies in connection with current results found in the literature.

Anisotropic connectivity and its influence on critical current densities, irreversibility fields, and flux creep inin situprocessed MgB2strands

“…Next, we can consider the anisotropy ratio, γ which has also been extensively studied. Based on measurements of films, single crystals, aligned crystals, and other samples, γ -values ranging from 1.1-1.7 [30][31][32] through 1.8-2.0 [33] to 3-7 [23,34] have been deduced. If anisotropy is responsible for the entire width of the resistive transition (1.6 K), equation ( 1) yields γ = 2.7.…”