Dirty Peierls transition to stripe phase in manganites

The nature of the phase transitions in La${}_{1-x}$Ca${}_x$MnO${}_3$ and Pr${}_{0.48}$Ca${}_{0.52}$MnO${}_3$ has been probed using heat capacity and magnetisation measurements. The phase transition associated with the onset of the stripe phase has been identified as second order. The model of a Peierls transition in a disordered system (a `dirty’ Peierls transition) is shown to provide an extremely good fit to this transition. In addition, an unexpected magnetic phase has been revealed in low temperature Pr${}_{0.48}$Ca${}_{0.52}$MnO${}_3$, associated with an excess heat capacity over a wide temperature range compared to La${}_{1-x}$Ca${}_x$MnO${}_3$.