Comparative studies on transport and magnetotransport behaviour of as-deposited and ex situ annealed A-type antiferromagnetic Nd _0.45Sr _0.55MnO ₃ films

Magnetic, transport and magnetotransport properties of A-type antiferromagnetic Nd _0.45Sr _0.55MnO ₃ films with different thicknesses grown on SrTiO ₃ (100) have been investigated before and after ex situ annealing processes. In contrast to the bulk system, all as-deposited films exhibit insulating behaviour due to the local Jahn-Teller distortion induced by in-plane tensile strain. The annealing process only induces an insulator-metal transition in ultrathin film with a thickness of 16 nm, resulting in metallically conductive behaviour and the transport properties similar to those of the bulk. This may be ascribed to the cooperative influences of changes in oxygen content and strain-induced d _x ²- _y ²-type orbital order owing to the annealing process. When a magnetic field of 70 kOe is applied, the metallic behaviour appears in a broad temperature range in the annealed film with 16 nm thickness and, the metallic behaviour is also observed in the annealed film with 32 nm thickness. The different effects of the external magnetic field on the transport properties of as-deposited and annealed Nd _0.45Sr _0.55MnO ₃ films are discussed.