  Among the class of strongly-correlated oxides, La1-xSrxMnO3 $-$ a half
metallic ferromagnet with a Curie temperature above room temperature $-$ has
sparked a huge interest as a functional building block for memory storage and
spintronic applications. In this respect, defect engineering has been in the
focus of a long-standing quest for fabricating LSMO thin films with highest
quality in terms of both structural and magnetic properties. Here, we discuss
the correlation between structural defects, such as oxygen vacancies and
impurity islands, and magnetism in La0.74Sr0.26MnO3/SrTiO3 (LSMO/STO) epitaxial
heterostructures by systematic control of the growth temperature and
post-deposition annealing conditions. Upon increasing the growth temperature
within the 500 $-$ 700 $^{\circ}$C range, the epitaxial LSMO films experience a
progressive improvement in oxygen stoichiometry, leading to enhanced magnetic
characteristics. Concurrently, however, the use of a high growth temperature
triggers the diffusion of impurities from the bulk of STO, which cause the
creation of off-stoichiometric, dendritic-like SrMoOx islands at the
film/substrate interface. As a valuable workaround, post-deposition annealing
of the LSMO films grown at a relatively-low temperature of about 500
$^{\circ}$C permits to obtain high-quality epitaxy, atomically-flat surface as
well as a sharp magnetic transition above room temperature and robust
ferromagnetism. Furthermore, under such optimized fabrication conditions
possible scenarios for the formation of the magnetic dead layer as a function
of LSMO film thickness are discussed. Our findings offer effective routes to
finely tailor the complex interplay between structural and magnetic properties
of LSMO thin films via temperature-controlled defect engineering.
