Anisotropy and internal field distribution of MgB2 in the mixed state at low temperatures

TL;DR

This study investigates the anisotropy and internal magnetic field distribution of MgB2 in the mixed state at low temperatures, revealing how penetration depth and anisotropy vary with magnetic field strength.

Contribution

It provides new insights into the field-dependent anisotropy of MgB2's penetration depth and internal field distribution through combined magnetization and muon spin relaxation measurements.

Findings

Penetration depth decreases with increasing magnetic field below 1 T.

Anisotropy of penetration depth increases with magnetic field.

No significant difference between anisotropies of penetration depth and coherence length.

Abstract

Magnetization and muon spin relaxation on MgB2 were measured as a function of field at 2 K. Both indicate an inverse-squared penetration depth strongly decreasing with increasing field H below about 1 T. Magnetization also suggests the anisotropy of the penetration depth to increase with increasing H, interpolating between a low Hc1 and a high Hc2 anisotropy. Torque vs angle measurements are in agreement with this finding, while also ruling out drastic differences between the mixed state anisotropies of the two basic length scales penetration depth and coherence length.