Harmonics of the AC susceptibility as probes to differentiate the various creep models

TL;DR

This study compares experimental measurements of AC susceptibility harmonics in type II superconductors with theoretical models to differentiate creep mechanisms, using Cole-Cole plots for enhanced sensitivity.

Contribution

It introduces a method to distinguish various vortex creep models through harmonic analysis and Cole-Cole plots, combining experimental data with numerical simulations.

Findings

Harmonics vary with temperature and AC field amplitude.

Cole-Cole plots provide detailed flux dynamic information.

Numerical models align well with experimental data.

Abstract

We measured the temperature dependence of the 1st and the 3rd harmonics of the AC magnetic susceptibility on some type II superconducting samples at different AC field amplitudes, hAC. In order to interpret the measurements, we computed the harmonics of the AC susceptibility as function of the temperature T, by integrating the non-linear diffusion equation for the magnetic field with different creep models, namely the vortex glass-collective creep (single-vortex, small bundle and large bundle) and Kim-Anderson model. We also computed them by using a non-linear phenomenological I-V characteristics, including a power law dependence of the pinning potential on hAC. Our experimental results were compared with the numerically computed ones, by the analysis of the Cole-Cole plots. This method results more sensitive than the separate component analysis, giving the possibility to obtain detailed information about the contribution of the flux dynamic regimes in the magnetic response of the analysed samples.