Impact of Growth Conditions on the Nature of Magnetism and Magnetotransport of Sm $_{0.55}$ Sr $_{0.45}$

The impact of growth conditions on the magnetic and electrical transport properties of oriented polycrystalline Sm_0.55Sr_0.45MnO₃ thin films prepared on nearly lattice matching (La_0.18 Sr_0.82 )(Al_0.59 Ta_0.41 )O₃ (LSAT) (100) single crystal substrates by nebulized spray pyrolysis has been studied. These films were deposited at substrate temperature TS = 473 K and then annealed at TA= 1273 K for 12 h in different ambient, viz., air and flowing oxygen. Although the PM-FM transition temperature remains unaffected by the growth conditions and occurs at TC = 130 K in all the films, the nature of magnetism is affected unambiguously. This is well evidenced by the change in 1) the nature of transition, 2) the magnetic moment, 3) coercivity, and 4) remanence; as a function of the synthesis conditions. The electrical transport properties, such as, insulator-metal transition (IMT), temperature coefficient of resistivity (TCR), and magnetoresistance (MR) are also affected by the variations in the growth conditions. The resistivity of all the films shows well-defined hysteretic behavior with respect to the thermal cycling and in the cooling cycle IMT occurs at lower temperature. The nature of the hysteresis and the residual resistivity also shows unambiguous dependence on the growth conditions. Our results demonstrate that oxygen annealing results in 1) reduced magnetic moment, 2) lower and broad FM- TC, 3) broadened IMT/lower TCR, and 4) smaller MR. The observed results have been explained in terms of the growth condition induced variations in the dimensionality and fractions of the competing FMM and AFM-CO phases.