<p>Carbon template (graphene oxide (GO) and carbon fiber (CF)) based magnetic nanomaterials like G-t-F (GO-Fe₃O₄), G-t-FC (GO-CoFe₂O₄), and CF-t-F (CF-Fe₃O₄) were synthesized for this work and successfully incorporated into poly (lactic acid) (PLA) matrix. Saturation magnetism was observed in the ferromagnetic region for synthesized templated materials. PLA-based composites were fabricated by solution casting and filler loading varied in the range of 0.5–2 wt.%. An investigation was conducted on the effects of magnetic filler's nature and structure on the material identities, thermal behaviors, and melt flow properties of the composites. Thermal stability was improved for MC-G-t-F-0.5, and nucleation properties were observed through DSC analysis. Rheology investigations under a magnetic field (current: 0–0.6 A) indicated that the flow behavior of composites is similar to that of magnetorheological fluid. Han plot, Cole–Cole Plot, and Van-Gurp-Palmen plot were studied, and network formation was observed under a magnetic field. Constitutive mechanical models such as Bingham, Casson, and Herschel-Bulkley (HB) were utilized to determine magnetorheological (MR) flow parameters. In the case of a representative magnetic particle nanocomposite, PLA/G-t-F, the dependency of yield stress with G-t-F weight fraction (φ) and magnetic flux density (B) was investigated and recorded. It was observed that composite melt behavior is dependent on the type of magnetic filler, weight fraction, and magnetic flux density.</p>