Temperature driven reversible breakdown of pseudomorphism in ultrathin Fe/Cu3Au films

We observe that ultrathin Fe/Cu3Au?001? films in the 6-13 A thickness range, beyond the thickness of pseudomorphism breakdown at room temperature, exhibit a temperature dependent structural phase transition in the range Tc 345-380 K. In the high temperature state the Fe film becomes pseudo- morphic, while breakdown of pseudomorphism reversibly occurs as the system is cooled below the transition temperature. The difference between substrate and overlayer thermal expansion coefficient is highlighted as the driving force for the observed transition.