Rigid vortices in MgB2

TL;DR

This study investigates magnetic relaxation in MgB2 bulks, revealing that vortices are rigid and their behavior aligns with the Kim-Anderson model, with relaxation properties influenced by sample thickness.

Contribution

The paper demonstrates that vortices in MgB2 are rigid and their flux creep behavior can be accurately described by the Kim-Anderson model, highlighting the impact of sample thickness.

Findings

Magnetic relaxation follows a logarithmic time dependence.

Activation energy decreases linearly with current density.

Activation energy increases linearly with sample thickness for thin samples.

Abstract

Magnetic relaxation of high-pressure synthesized MgB$_2$ bulks with different thickness is investigated. It is found that the superconducting dia-magnetic moment depends on time in a logarithmic way; the flux-creep activation energy decreases linearly with the current density (as expected by Kim-Anderson model); and the activation energy increases linearly with the thickness of sample when it is thinner than about 1 mm. These features suggest that the vortices in the MgB$_2$ are rather rigid, and the pinning and creep can be well described by Kim-Anderson model.