Harmonic AC magnetic susceptibility analysis of FeSe crystals with composite morphology

Abstract

The AC magnetic response of multi-domain FeSe crystals has been explored by means of fundamental and third harmonic AC magnetic susceptibility (ACMS) analysis. Our previous studies have revealed a complex morphology which especially modifies the mixed state properties. The effects were expressed by an additional 'pseudo' peak feature of the magnetic hysteresis and in the present study we analyze its vortex dynamics nature and irreversibility behavior in the context of ACMS. We find that the effect is detectable mainly with the sensitive third harmonic component and especially at high AC field frequencies. From the analysis, the temperature dependence of the 'pseudo' peak effect at different DC fields ranges was determined, confirming the previously established superconductor-normal metal-superconductor type links between the domains in the crystal. The irreversibility line, the most important parameter for high power applications, shows a typical glass/liquid transition in the vortex matter. In addition we have observed surface barrier effects and vortex avalanche activity, the behavior of which appears to be influenced by the superconducting and magnetic nature coexistence and morphology. The presented results show the effective application of the harmonic AC magnetic susceptibility technique for a versatile analysis of complex nonlinear phenomena in materials with a sophisticated AC magnetic response.

Pinning Energy and Evidence of Granularity in the AC Susceptibility of an YBa2Cu3O7-x Superconducting Film

“…This work deals with the AC magnetic response of an YBCO thin film by studying the imaginary component of the AC susceptibility. The choice to perform and measure the AC susceptibility derives from the fact that this technique is very sensitive to the presence of granularity in the superconductors because it can reveal the complex electromagnetic properties of the granular structure of materials [26][27][28][29][30][31][32][33][34][35]. In particular, the AC susceptibility has been studied as a function of the AC amplitude χ 1 ′′ (h AC ), the temperature χ 1 ′′ (T), and the DC magnetic field χ 1 ′′ (H DC ).…”

High-Frequency ac Susceptibility of Iron-Based Superconductors

“…It is shown that a further analysis of the complex AC susceptibility data allows one to obtain the London penetration depth and therefore the superfluid density, thus enabling the validation of theories and models concerning the mechanisms of superconductivity in the IBS. For this goal, the high frequency of this technique offers an advantage with respect to conventional AC susceptometry, for which the determination of is challenging [ 16 ] because of the long wavelength and the geometry associated with those experiments [ 17 ], which is more suitable for the study of vortex physics and pinning [ 18 , 19 , 20 ] and of nonlinearity [ 21 , 22 ]. In Section 3 of this paper, we present and discuss the characterization of several IBS systems, belonging to different IBS families.…”

Mixed state properties analysis in AC magnetic field of strong pinning Fe(Se,Te) single crystal

“…The presence of these different regimes causes an AC magnetic response generating fundamental and superior harmonic curves with complex shapes [21,23,24]. In particular, the third harmonic has the strongest signal (after the fundamental one) and for this reason it is the most analyzed also because it gives direct information on the vortex dynamics of the sample [25][26][27][28][29][30]. In the present study, we analyze the ACMS of a Fe(Se,Te) system belonging to the 11 family of the IBS, which is particularly interesting due to its very high value of the upper critical field and of the critical current density even at high magnetic fields [9,31,32].…”