Oxygen vacancy-induced enhancement in magnetism and magneto-transport properties in Sm${}_{0.55}$Sr${}_{0.45}$MnO${}_3$ thin films

Polycrystalline Sm${}_{0.55}$Sr${}_{0.45}$MnO${}_3$ (SSMO) thin films (thickness ~ 100 nm) were prepared on nearly lattice matching LSAT (100) single crystal substrates by ultrasonic nebulized spray pyrolysis, and impact of oxygen vacancy on magnetic and high field magneto-transport properties are investigated. The X-ray diffraction θ-2θ scan reveals that these films (i) have very good crystallinity, (ii) oriented along out-of-plane c-direction, and (iii) are under small tensile strain. The impact of oxygen vacancy results into (i) higher value of paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature, i.e., T${}_C$/T${}_{IM}$, (ii) sharper PMI-FMM transition, as confirmed by higher temperature coefficient of resistance (TCR), (iii) higher value of magnetization and magnetic saturation moment, and (iv) higher value of magnetoresistance. The magnetic state at T < T${}_C$ is akin to cluster glass, which is formed by the presence of charge-ordered-antiferromagnetic clusters in the ferromagnetic matrix. We suggest here that oxygen vacancy favors ferromagnetic metal phase while oxygen vacancy annihilation leads to antiferromagnetic-charge-ordered insulator phase. The observed results have been explained in terms of the growth condition-induced variations in the dimensionality and fractions of the competing ferromagnetic metal and antiferromagnetic-charge-ordered insulator phases.