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

Abstract

In the past decades, ferromagnet-metalloid alloy films of Co-Fe-B have been widely used in new magnetic devices due to their excellent performance, such as easy industrial-scale fabrication, and considerable ability for tunneling magnetoresistance and perpendicular magnetic anisotropy. However, the insufficient thermal tolerance and interfacial state densities in the typical CoFeB/MgO system limits devices optimization. Because of the improvement in thermal stability and interfacial properties by carbon element replacement, new 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 (Co 0.5 Fe 0.5) x C 1-x films grown on silicon (001) substrates. The addition of carbon changes the Co-Fe-C films from nanocrystalline bcc 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 linewidth of 25 Oe at X-band, extremely low Gilbert damping of 0.002 and up to 500℃ thermal stability. The large saturated magnetostriction constant and piezomagnetic coefficient result from coexistence of nanocrystalline bcc and amorphous phases. The extremely low Gilbert damping is related to the minimized density of states around Fermi energy of the alloys induced by carbon doping. The combination of these properties makes Co-Fe-C films a promising candidate to be widely used in voltage tunable magnetoelectric devices and microwave magnetic devices.

Roadmap on Magnetoelectric Materials and Devices

“…For alternative modes of operation or sensor designs, like SAW-based sensors [396], bulk piezoelectric materials like quartz, also in combination with ZnO films [397], are utilized. For the magnetostrictive phase, a high piezomagnetic coefficient at the working point of the sensor is an apparent requirement, favoring soft-magnetic amorphous thin films like FeCoSiB [398], FeGaB [399], FeGaC [400], FeCoC [401] or similar soft-magnetic alloys with high saturation magnetostriction for ME sensor applications. Laminating the materials in thin-film sensors provides an additional option to improve the soft-magnetic characteristics, allowing also for the reduction of eddy currents by laminating with an insulator.…”

“…Magnetostriction constants as high as 80 ppm where achieved in the case of FeGaC [400], while maintaining considerable soft magnetic properties. A promising approach for improving magnetostriction is the incorporation of nanocrystals within the amorphous films [401]. Second, the exact alignment of the magnetization in the sensors, most relevant for obtaining high signal amplitude and thus maximum sensitivity, is of high relevance.…”

Mechanically driven SMR-based NEMS magnetoelectric antennas

“…The source of UMA can be in principle attributed to magnetocrystalline anisotropy, substrate surface topography, magnetic field induced anisotropy and stress induced anisotropy 38 . Due to the amorphous structure of the thick seed layer and smooth substrate surface, we assume only contributions from the induced anisotropies to the UMA.…”

“…Due to the amorphous structure of the thick seed layer and smooth substrate surface, we assume only contributions from the induced anisotropies to the UMA. Wang et al 38 demonstrated the stress-induced UMA in FeCoC films. However, the deposited film stress was not analysed.…”

A Review of Thin-Film Magnetoelastic Materials for Magnetoelectric Applications

“…In 2019, Wang investigated the magnetostrictive behavior of (Co 0.5 Fe 0.5 ) x C 1-x alloy thin films with different carbon content [112]. Figure 13 presents the magnetostriction results of these Co-Fe-C films with increasing carbon content as a function of the in-plane driving magnetic field.…”