This work reports magnetic field direction dependent second magnetisation peak (SMP) anomaly in single crystals of oxygenated \(\hbox {YBa}_{2}\hbox {Cu}_{3-\hbox {x}}\hbox {Al}_{\hbox {x}}\hbox {O}_{6+\delta }\) for \(\mu _0H ||\) ab. Detailed investigations on crystal A revealed the direction dependence of SMP anomaly at temperatures below 25 K, above which the direction dependence vanishes. The state of spatial order of the vortex lattice was found to be correlated to the vortex lattice symmetry that underwent a change at certain fields and was captured via single flux jumps observed in the third and fifth quadrant of magnetisation hysteresis loops. Bean’s critical state profiles drawn to explain the flux jumps required the presence of clusters of \((\hbox {Al}-\hbox {O}-\hbox {Cu}-\hbox {O}-\hbox {Cu})_{n}\) in the basal plane of \(\hbox {YBa}_{2}\hbox {Cu}_{3-\hbox {x}}\hbox {Al}_{\hbox {x}}\hbox {O}_{6+\delta }\) with closely lying binding energies. Large full width at half maximum observed in Cu, O, Y and Ba photoelectron spectra confirmed the validity of the proposed cluster model. A vortex phase diagram incorporating all features in the magnetisation hysteresis loops has been made for oxygenated \(\hbox {YBa}_{2}\hbox {Cu}_{3-\hbox {x}}\hbox {Al}_{\hbox {x}}\hbox {O}_{6+\delta }\) for \(\mu _0H\) || ab depicting various phases.
