PC-P-10
Asymmetric magnetic hysteresis loops in FeSe1−xTex single crystals
16:45-18:15 29/11/2023
David Uhrig1,2,3, Grant Williams2,3, Gabriel Bioletti1,2, and *Shen V. Chong1,2,3
1. Robinson Research Institute, Victoria University of Wellington, New Zealand
2. School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington,New Zealand
3. MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellingt
Superconductors typically exhibit symmetric magnetic hysteresis loops (MHLs). That is, the magnitude of the magnetisation when increasing the magnetic field, Mincr(B), and decreasing the field, Mdecr(B), is approximately equal, leading to a symmetric MHL with respect to M = 0. This is also true for FeSe1−xTex superconductors reported in the literature [1-4]. However, some of the FeSe1−xTex samples that we have investigated exhibit a pronounced asymmetric hysteresis loop with respect to the M = 0 axis. Specifically, whilst Mincr(B) still exhibits a typical magnetisation profile, Mdecr(B) is close to zero. The observation of such asymmetry is of special interest as it suggests abnormal pinning behaviour that is rarely reported in the iron-based superconductors [5-8].
We found that these MHLs are not measurement artefacts, but intrinsic to the nature of several investigated samples. The asymmetric state was found to be unstable upon exposing the samples to atmosphere for a prolonged period. The sweep-rate-dependent MHL and relaxation rate analysis showed that the asymmetry is a result from weak effective pinning barrier that leads to a fast-decaying magnetisation in the descending field branch.
Based on these observations, we proposed a model (Fig. 1) based on the interplay of weak bulk pinning and a strong surface barrier to explain the observed asymmetric behaviour and the different relaxation regimes. In this model, the total magnetisation is given by the sum of the contribution due to surface pinning and bulk pinning, M = Msurf + Mbulk. The bulk pinning is described by the simple Bean model, where the flux gradient is assumed to be independent of the applied field. The surface barrier is assumed to be independent of both the applied field and the flux profile inside the superconductor. Here, we considered the surface barrier to be of Bean-Livingston type where flux entry is prevented, but not flux exit [9,10].
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We acknowledge funding by the Marsden Fund of New Zealand (VUW1608) and the MacDiarmid Institute for Advanced Materials and Nanotechnology.
