Magnetostriction, Soft Magnetism, and Microwave Properties in Co−Fe−C Alloy Films

In the past decades, ferromagnet-metalloid alloy films of Co-Fe-B have been widely used in alternative magnetic devices due to their excellent performance, such as easy industrial-scale fabrication, considerable ability for tunneling magnetoresistance and perpendicular magnetic anisotropy. However, the insufficient thermal tolerance and interfacial state densities in the typical Co-Fe-B/MgO system limits the devices' optimization. Because of the improvement in thermal stability and interfacial properties by carbon element replacement, alternative theoretical and experimental work on Co-Fe-C alloy film properties have been reported. Here, we report on the magnetostrictive behavior, soft magnetism, and microwave properties of a series of (Co0.5Fe0.5)(x)C1-x films grown on silicon (001) substrates. The addition of carbon changes the Co-Fe-C films from nanocrystalline body-centered-cubic to an amorphous phase and leads to a high saturated magnetostriction constant of 75 ppm, high piezomagnetic coefficient of 10.3 ppm/Oe, excellent magnetic softness with a low coercivity less than 2 Oe, narrow ferromagnetic resonance line width of 25 Oe at the X band, extremely low Gilbert damping of 0.002, and up to 500 degrees C thermal stability. The large saturated magnetostriction constant and piezomagnetic coefficient result from the coexistence of nanocrystalline body-centered-cubic and amorphous phases. The extremely low Gilbert damping is related to the minimized density of states around the Fermi energy of the alloys induced by carbon doping. The combination of these properties makes Co-Fe-C films promising candidates to be widely used in voltage-tunable magnetoelectric devices and microwave magnetic devices.