We report an investigation of the effects of variation of composition on the properties of yttrium iron garnet films grown on yttrium aluminium garnet substrates by multi-beam pulsed laser deposition. The ferromagnetic resonance linewidth is used as a quality factor: a significant variation is noticed from changing composition, with an experimentally observed optimum at Y3.5Fe4.5O12. (C) 2014 Elsevier B.V. All rights reserved.