Magnetoplasmonic sensors are attractive candidates for ultrasensitive chemical and biomedical sensor applications.A variety of ferromagnetic metal thin films have been used for magnetoplasmonic device applications, yet the dependence of sensor performance on the optical and magneto-optical properties of ferromagnetic metal materials has been rarely studied. In this work, we report the study of enhanced magneto-optical Kerr effect(MOKE) and sensing performance in Au∕Fe_xCo_(1-x)bilayer magneto-optical surface plasmon resonance(MOSPR) transducers.The optical constants of Fe_xCo_(1-x)(x = 0, 0.29, 0.47, 0.65, and 1) in a sputter-deposited Au∕Fe_xCo_(1-x)device are characterized by the attenuated total internal reflection(ATR) method. Fe_xCo_(1-x)thin films show different MOKEs as a function of the chemical concentration, with the highest transverse MOKE signal observed in Fe_0.7Co_0.3.Index sensing performance is closely related to the material’s optical and magneto-optical constants. By studying the sensing performance in the parameter space of the Au∕Fe_xCo_(1-x)bilayer thicknesses, the highest sensitivity is found to be 0.385(theoretical) and 0.306 RIU~(-1)(experimental) in the Au∕Fe_0.7Co_0.3 MOSPR devices. Our research highlights the influence of the optical properties of ferromagnetic material to device sensitivity in MOSPR transducers. The high sensitivity in Au∕Fe_xCo_(1-x)MOSPR devices make these structures attractivecandidates for chemical and biomedical sensing applications. Magnetoplasmonic sensors are attractive candidates for ultrasensitive chemical and biomedical sensor applications. A variety of ferromagnetic metal thin films have been used for magnetoplasmonic device applications, yet the dependence of sensor performance on the optical and magneto-optical properties of ferromagnetic metal materials has been at least studied . In this work, we report the study of enhanced magneto-optical Kerr effect (MOKE) and sensing performance in Au / Fe_xCo_ (1-x) bilayer magneto-optical surface plasmon resonance (MOSPR) transducers. The optical constants of Fe_xCo_ (1 -x) (x = 0, 0.29, 0.47, 0.65, and 1) in a sputter-deposited Au / Fe_xCo_ (1-x) device are characterized by the attenuated total internal reflection (ATR) thin films show different MOKEs as a function of the chemical concentration, with the most transverse MOKE signal observed in Fe_0.7Co_0.3. Index sensing performance is closely related to the material’s optical and magneto-optical constants. By studying the sensing performance in the parameter space of the Au / Fe_xCo_ (1-x) bilayer thicknesses, the highest sensitivity is found to be 0.385 (theoretical) and 0.306 RIU ~ (-1) (experimental) in the Au / Fe_0. Our research highlights the influence of the optical properties of ferromagnetic material to device sensitivity in MOS transducers. The high sensitivity in Au / Fe_xCo_ (1-x) MOSPR devices make these structures attractive conditions for chemical and biomedical sensing applications.