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A universal phase diagram for weakly pinned low-T c type-II superconductors is revisited and extended with new proposals. The low-temperature "Bragg glass" phase is argued to transform first into a disordered, glassy phase upon heating. This glassy phase, a continuation of the high-field equilibrium vortex glass phase, then melts at higher temperatures into a liquid. This proposal provides an explanation for the anomalies observed in the peak effect regime of 2H-NbSe 2 and several other low-T c materials which is independent of the * Corresponding Author, Email:menon@imsc.ernet.in † Corresponding Author, Email:shampa@mailhost.tifr.res.in 1 microscopic mechanisms of superconductivity in these systems.

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History-dependent metastable states with different bulk properties are formed in the vortex state of the type-II superconductor 2H-NbSe2. Magnetic measurements demonstrate the difference between the shielding responses of a field- and a zero-field-cooled state, and provide a procedure for switching the system from one state to the other.

Magnetic screening response of the superconductor 2H-NbSe 2 with varying pinning reveals a rich evolution of the peak effect from a history-independent sharp anomaly to a broad and strongly history dependent effect with internal structure. The results display a stepwise disordering of the vortex lattice through transformations affected by both thermal fluctuations and quenched disorder. ͓S0163-1829͑99͒03309-3͔ PHYSICAL REVIEW B