The magnetism of the double perovskite compounds SLFCOx ($x$ = 0, 1, 2) are contrasted using magnetization, neutron diffraction and electron paramagnetic resonance with the support from density functional theory calculations. LFCO is identified as a long-range ordered antiferromagnet displaying a near-room temperature transition at $T_N$ = 270~K, accompanied by a low temperature structural phase transition at $T_S$ = 200~K. The structural phase transformation at $T_S$ occurs from $Roverline{3}c$ at 300~K to $Pnma$ at 200~K. The density functional theory calculations support an insulating non-compensated AFM structure. The long-range ordered magnetism of LFCO transforms to short-range glassy magnetism as La is replaced with Sr in the other two compounds. The magnetism of LFCO is differentiated from the non-equilibrium glassy features of SFCO and SLFCO using the {em cooling-and-heating-in-unequal-fields} (CHUF) magnetization protocols. This contransting magnetism in the SLFCOx series is evidenced in electron paramegnetic resonance studies. The electronic density-of-states estimated using the density functional theory calculations contrast the insulating feature of LFCO from the metallic nature of SFCO. From the present suite of experimental and computational results on SLFCOx, it emerges that the electronic degrees of freedom, along with antisite disorder, play an important role in controlling the magnetism observed in double perovskites.
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