We observe a strong effect of surfactant structure on the aggregation of ferromagnetic nanoparticles in nematic liquid crystal (LC) hosts, and the colloidal stability and ordering of the resulting nematic matrix. We find that ferromagnetic nanoparticles coated with surfactants that possess terminal mesogenic groups induce minimal aggregation of the nanoparticles, resulting in a 1.5 times reduction in the value of the Frederikscz transition field in comparison with the parent LC host.