Phys. Rev. B 68, 134444 (2003)

M. Ziese, H. C. Semmelhack, and K. H. Han

Abstract

The microstructural, magnetic, and magnetotransport properties of La_0.7Ca_0.3MnO₃ films epitaxially grown on SrTiO₃ substrates were studied as a function of film thickness. Films with a thickness above 70 nm show bulklike properties consistent with the relaxed film growth. Very thin films are fully strained and are insulating and ferromagnetic in zero field. Under the application of a large magnetic field a strongly hysteretic metal-insulator transition is seen accompanied by a transition to a ferromagnetic state with larger saturation magnetization. The field-induced metallic state is shown to be anisotropic with metallic domains extending along the field direction. An analysis of the microstructure shows that the strain variation across growth islands is far too small to induce strain-related phase separation on length scales of the order of 100 nm. It is concluded that the insulating state is a property of homogeneously strained manganite films and arises from a weakening of the double-exchange interaction due to the ordering of atomic orbitals.