Vortex dynamics behavior with third harmonic ac-susceptibility for nano Fe-doped MgB2 superconductor

Abstract

In the present study, the nano Fe-doped MgB2 samples with different doping contents (0 wt% ≤ x ≤ 6 wt%) were synthesized by the solid-state reaction technique. The fundamental and third harmonic real and imaginary components of ac-susceptibility were measured with an ac-applied field of Hac = 0.5 Oe under the different frequency range f = 1–3 kHz. The amplitude of the peaks in the first harmonic imaginary component as a function of temperature, $${\chi ^{\prime\prime}_1}(T)$$ plots enhances regularly as we increase the frequency and shifted towards the higher temperature region. The highest amplitude of the peak is shown by 3 wt% doped sample among the undoped and doped sample in $${\chi ^{\prime\prime}_1}(T)$$ plot. The χ3″ reveals the sinusoidal oscillation with maxima and minima of the ratio δ, a parameter associated with the penetration depth of the ac-applied field. The amplitude of the real component χ3′ is smaller than the imaginary component of χ3″ in third harmonic ac-susceptibility measurements. The 6 wt% nano-Fe doped MgB2 sample shows the multiple real and imaginary peaks of third harmonic ac-susceptibility, χ3. The irreversibility line (IL) is shifted towards the higher temperature site with the increases of frequency. The slope of the IL increases with the increase of frequency.