Hysteresis Effects in Magnetovoltage Measurements in Superconducting ${\rm MgB}_{2}$

Hysteresis effects in superconducting MgB₂ have been studied systematically by magnetovoltage measurements (V-H curves) as a function of transport current (I), temperature (T) and sweep rate of external magnetic field (H), (dH/dt). It was observed that time dependent effects appear as the field sweep rate (dH/dt) varies. This reflects itself as a decrease in the width of V-H loops with decreasing of dH/dt. The dissipation measured in V-H curves does not change as the sweep rate of external magnetic field is varied. It was observed that the measured dissipation in V-H curves is independent of field orientation of H with respect to I. Furthermore, it was observed that there is a significant asymmetry in V-H loops between forward and reverse regions. The physical observations were interpreted mainly in terms of flux de-trapping/trapping and thus the difference in the local fields trapping in the grains between increasing and decreasing branches.