Irreversibility effects and low field magnetovoltage measurements in superconducting MgB2 near the critical temperature T (c)
Yükleniyor...
Dosyalar
Tarih
2013
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Springer
Erişim Hakkı
info:eu-repo/semantics/closedAccess
Özet
We have investigated the hysteresis effects in magnetovoltage measurements (V-H curves) in a polycrystalline superconducting MgB2 near critical temperature T (c) . The measurements were carried out as functions of temperature (T) and transport current (I), and sweep rates of the external magnetic field (dH/dt) and perpendicular and parallel orientations of external magnetic field (H) with respect to I, i.e., the V (aSyen)-H curves for and V (ayen)-H curves for . The hysteresis effects related to both forward and reverse regions of V-H curves were interpreted within two level magnetic system mainly flux trapping inside the grains. A series of expansion of V(H) in terms of H was approximated to describe macroscopically the experimental V-H curves. The analysis of zero field I-V curves obtained by standard and reverse procedures gives an evidence of nearly absence of macroscopic surface pinning. The instabilities in V-H curves were interpreted in terms of defective flow of flux lines and also local fluctuations in magnetic flux structure. Further, the anisotropic effects in MgB2 sample were explored by measuring the angular dependence of dissipation at the fixed values of T, H and I by varying the angle (theta) between H and I, i.e., V-theta curves. The analysis of V-theta curves reveals that the measured dissipation does not exhibit any agreement with the Lorentz force driven free flux motion, V(theta)similar to sin(2)(theta). This suggests that the anisotropic effects are screened by the random distribution of the grains in different sizes.
Açıklama
Anahtar Kelimeler
Flux Dynamics, MgB2, Magnetoresistance, Flux Pinning
Kaynak
Journal Of Superconductivity And Novel Magnetism
WoS Q Değeri
Q3
Scopus Q Değeri
Q3
Cilt
26
Sayı
12
