Abstract
To explore the further possibilities of nanometer-thick ferromagnetic films (ultrathin ferromagnetic films), we investigated the ferromagnetic resonance (FMR) of 1 nm-thick Co film. Whilst an FMR signal was not observed for the Co film grown on a SiO2 substrate, the insertion of a 3 nm-thick amorphous Ta buffer layer beneath the Co enabled the detection of a salient FMR signal, which was attributed to the smooth surface of the amorphous Ta. This result implies the excitation of FMR in an ultrathin ferromagnetic film, which can pave the way to controlling magnons in ultrathin ferromagnetic films.
Highlights
To explore the further possibilities of nanometer-thick ferromagnetic films, we investigated the ferromagnetic resonance (FMR) of 1 nm-thick Co film
The thickness of ferromagnetic metal films often used in FMR studies in spintronics is typically greater than 5 nm, because the surface roughness of the substrate beneath the ferromagnetic metal hampers the observation of a clear FMR signal
Given the success of the substantial magnetization control in ultrathin Co by g ating[1,2], efficient and tunable magnon creation in ultrathin ferromagnetic metals under FMR can provide a path to electric-field control of magnons, because the number of magnons is proportional to the square root of the total magnetization and the coupling strength between magnons and photons is collectively enhanced by square root of number of magnons[12]
Summary
To explore the further possibilities of nanometer-thick ferromagnetic films (ultrathin ferromagnetic films), we investigated the ferromagnetic resonance (FMR) of 1 nm-thick Co film. Studies on the spintronic nature of ultrathin films have been expanded to include nonmagnetic metals, and the discovery of a gate-tunable inverse spin Hall effect in ultrathin Pt (2 nm thickness) has opened the field of tunable spin–orbit interaction (SOI)[3]. A common physics among the magnetization control of ultrathin ferromagnetic films and the tunable SOI in ultrathin nonmagnetic films is a substantial shift of the Fermi level under a strong gate electric field[4,5]. Investigation of spin physics using ferromagnetic resonance (FMR) is pivotal in modern spintronics It has been used in a wide range of studies from both fundamental and applied physics, including those related to the generation of spin c urrent[6] and a spin-torque diode e ffect[7]. The key to achieving FMR is utilization of smooth surface of amorphous Ta layer
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