Multiple Magnetization Peaks and New Type of Vortex Phase Transitions in Ba0.6K0.4Fe2As2

TL;DR

This study investigates multiple magnetization peaks in Ba0.6K0.4Fe2As2 single crystals, revealing complex vortex phase transitions and flux dynamics across different temperature regions.

Contribution

It reports the discovery of a third magnetization peak and identifies a new type of vortex phase transition in this iron-based superconductor.

Findings

Observation of flux jumps and multiple magnetization peaks.

Identification of a new vortex phase transition.

Correlation between magnetization peaks and vortex pinning/relaxation.

Abstract

Magnetization and its relaxation have been measured on Ba0.6K0.4Fe2As2 single crystals with Tc = 39 K. The magnetization hysteresis loops (MHLs) exhibit flux jumps in the low temperature region, and a second peak-effect in the intermediate temperature region, especially when the field sweeping rate is low. Interestingly a third magnetization peak can be easily observed on the MHLs in the high temperature region. Further analysis find that the first magnetization peak is very sharp, which is associated with the strong vortex pinning. However the first dip of the MHL corresponds to a moderate relaxation rate, then a second peak appears accompanied by a vanishing vortex motion. Finally a third magnetization peak emerges and the vortex motion becomes drastic beyond this threshold. The novel features accompanying the second magnetization peak suggest a new type of vortex phase transition.