  We report a magnetocaloric study of the peak effect and Bragg glass
transition in a Nb single crystal. The thermomagnetic effects due to vortex
flow into and out of the sample are measured. The magnetocaloric signature of
the peak effect anomaly is identified. It is found that the peak effect
disappears in magnetocaloric measurements at fields significantly higher than
those reported in previous ac-susceptometry measurements. Investigation of the
superconducting to normal transition reveals that the disappearance of the bulk
peak effect is related to inhomogeneity broadening of the superconducting
transition. The emerging picture also explains the concurrent disappearance of
the peak effect and surface superconductivity, which was reported previously in
the sample under investigation. Based on our findings we discuss the
possibilities of multicriticality associated with the disappearance of the peak
effect.
