Percolative conduction in the half-metallic-ferromagnetic and ferroelectric mixture of (La,Lu,Sr)MnO3

Abstract

The immiscibility between rhombohedral La5/8Sr3/8MnO3 and hexagonal LuMnO3 leads to a mum-scale heterogeneous mixture of half-metallic-ferromagnetic and insulating-ferroelectric phases. Electronic conduction of the mixture exhibits nearly ideal percolation behavior in the paramagnetic state with a threshold of 0.224(5) metal volume fraction and a resistivity scaling exponent t=2.1+/-0.1, consistent with the predicted universal behavior of classical percolation. However, far below T-C, t increases to 2.4+/-0.1, probably resulting from intergrain tunneling. Therefore, this system represents a unique example of the temperature-induced crossover from universal to nonuniversal behavior of t.