| Description |
Owing to the presence of competing interactions like vortex-vortex, pinning potential and thermal fluctuations, weakly pinned type-II superconductor is ideal to investigate dynamics of VL. Where vortex-vortexinteraction tends to order the VL, disorder in the VL is usually introduced by pinning and thermal fluctuations. It is due to interplay between suchcompeting interactions, the critical current display anomalous increase below upper critical field known as “peak effect”. Moreover, it has been accepted that VL at low temperature is ordered or disordered, will depend, if the VL is cooled in field or in zero field from the normal state. In the present study, we have investigated zero field cool (ZFC) and field cool (FC) state in lightly doped Co0.0075NbSe2 single crystals through susceptibility measurements.In ZFC protocol, the sample was cooled in zero field from normal state to the lowest temperature, then magnetic field was applied and susceptibility as a function of temperature was measured while heating. For FC, the sample was first cooled in field up to lowest temperature, then susceptibility as a function of temperature was measured while heating. At regular temperature intervals, a magnetic field pulse of 300 Oe was applied to relax the vortex lattice to its stable configuration. We found that, pulsing relaxes the FC state close to the ZFC. However, ZFC state created at low temperature could not relax to its stable configuration with increase in temperature unless the VL is shaken by magnetic field pulse. The effect is significant at low field and high temperatures near the onset of peak effect. Above 0.25T, the low temperature regime remains unaltered by pulsing, while in the peak effect region, ordered ZFC state getsshattered and its diamagnetic response increases and come close to disordered FC state. However below 0.25T, in the peak effect region, pulsing induces enhancement in ordering as compare to unperturbed ZFC state, manifested by decreased diamagnetic response. Moreover, the peak effect become sharper when the periodic pulse is applied on the ZFC state. The ZFC VL images captured at different fields using STM also reveals similar observations. At low fields and temperature slightly below the onset of peak effect, pulsing orders the VL. On the other hand, at high fields pulsing introduces disorder in the VL.
|