Anisotropy of the Upper Critical Field and Critical Current in Single Crystal MgB$_2$

TL;DR

This study investigates the anisotropic properties of the upper critical field and critical current in single crystal MgB₂, revealing temperature-dependent anisotropy and specific magnetic field effects.

Contribution

First comprehensive measurement of $H_{c2}$ in MgB₂ across the entire temperature range for different orientations, highlighting anisotropy variation.

Findings

Anisotropy ratio $ ightarrow$ 5 at low T, 2 near $T_c$

Peak effect observed in susceptibility at 2 T parallel to c-axis

Critical current density shows a sharp maximum for H parallel to ab-plane

Abstract

We report on specific heat, high magnetic field transport and $ac-$susceptibility measurements on magnesium diboride single crystals. The upper critical field $H_{c2}$ for magnetic fields perpendicular and parallel to the Mg and B planes is presented for the first time in the entire temperature range. A very different temperature dependence has been observed in the two directions which yields to a temperature dependent anisotropy with $\Gamma \sim$ 5 at low temperatures and about 2 near $T_c$. A peak effect is observed in susceptibility measurements for $H \sim $2 T parallel to the $c-$axis and the critical current density presnts a sharp maximum for $H$ parallel to the ab-plane.