Strain-controlled electronic properties and magnetorelaxor behaviors in electron-doped CaMnO₃ thin films

We have fabricated epitaxial thin films of electron-doped manganite Ca _1-xCe_x MnO₃ (CCMO) with 0≤x≤0.08. The transport properties of CCMO films are very sensitive to substrate-controlled epitaxial strain. For the CCMO (x=0.05) film, the metallic transport characteristic is observed only on a nearly lattice-matched NdAlO₃ (NAO) substrate, while tensilely and compressively stressed films are insulating. The CCMO (x=0.06) film on the NAO substrate shows a large magnetoresistance characteristic of a magnetorelaxor. This behavior can be explained in terms of the phase separation and the irreversible growth of the metallic domain in antiferromagnetic insulating matrix.