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

The immiscibility between rhombohedral La(5/8)Sr(3/8)MnO3 and hexagonal LuMnO3 leads to a microm-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.