Impact of Co doping on the magnetic and transport properties of FeRh

FeRh undergoes a first-order phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) state at ∼370 K, which is highly sensitive to strain and compositional changes. In this study, we investigate the magnetic and electronic properties of Co-doped FeRh films fabricated using a co-sputtering technique, to address how the magnetic transition behavior is influenced by the doping in FeRh films. By adjusting Co sputtering gun currents (=0, 5, 8, and 10 mA), we achieve Co doping levels from 1 to 2 at. %, where initial Co atoms (for 5 and 8 mA) substitute Rh sites, while doped Co levels (for 10 mA) begin to occupy Fe sites with unchanged Co doping level of 2 at. %. We find that Co substitution significantly lowers the transition temperature, attributed to an enhancement of the FM phase due to the contribution of magnetic Co doping. Furthermore, the Co doping leads to a remarkable increment in the magnetoresistance ratio during the transition, reaching up to 190% for only 2 at. % Co doping, while keeping the magnetization change. The Hall effect measurements indicate a slight reduction in carrier density with Co doping, maintaining changes in carrier type across the phase transition. These results highlight the tunable magnetic phase transition and resistance changes in Co-doped FeRh films. This study provides valuable insights into the complex physics underlying the Co doping in FeRh films, emphasizing their scientific value in understanding the mechanism of the AFM–FM transitions in achieving high magnetoresistance.