Ferromagnetic Resonance of a Single Magnetochiral Metamolecule of Permalloy

Abstract

We investigate the ferromagnetic resonance (FMR) of a single chiral structure of a ferromagnetic metal-the magnetochiral (MCh) metamolecule. Using a strain-driven self-coiling technique, micrometersized MCh metamolecules of metallic permalloy (Py) are fabricated without any residual Py films. The magnetization curves of ten Py MCh metamolecules obtained by an alternating gradient magnetometer show soft magnetic behavior. In cavity FMR with a magnetic-field sweep and coplanar-waveguide (CPW) FMR with a frequency sweep, the Kittel-mode FMR of the single Py metamolecule is observed. The CPW-FMR results, which are consistent with the cavity-FMR results, bring about the effective g factor, effective magnetization, and Gilbert damping of the single metamolecule. Together with calculations using these parameters, the angle-resolved cavity FMR reveals that the magnetization in the Py MCh metamolecule is most likely to be the hollow-bar type of configuration when the external magnetic field is applied parallel to the chiral axis, although the expected magnetization state at remanence is the corkscrew type of configuration.

Microwave Spectroscopy of a Single Permalloy Chiral Metamolecule on a Coplanar Waveguide

“…The μ 0 M eff value of the Py chiral metamolecule is smaller than that of the metallic Py thin film (1.05 T) given in the literature [21]. The small μ 0 M eff value indicates surface and interface anisotropies due to unsaturated spins [22] in the Py films on the SU8 film for the Py metamolecule [8]. Since these fitting parameters are reasonable values, the dip is caused by the Kittel-mode FMR in the Py thin film of the metamolecule.…”

“…3(a) is thus a fitting curve using the Kittel formula [20] for a magnetic film with H ext applied in the direction parallel to the film plane. The fitting procedure results in a g eff value of 2.1590 AE 0.0082 and a μ 0 M eff value of 681.77 AE 9.01 mT [8]. The μ 0 M eff value of the Py chiral metamolecule is smaller than that of the metallic Py thin film (1.05 T) given in the literature [21].…”

“…While ac magnetic fields are parallel to the y axis at the signal-line center, those at the edge of the CPW signal line have a z-direction component parallel to the chiral axis. In this way, the spin-wave resonance signals accompanied by the Kittel mode FMR observed in the metamolecule are traced back to the localized resonance modes due to the inhomogeneous ac fields [8,28]. In general, the frequency of magnetic resonances, for example, Kittel-mode FMR and spin-wave resonance, is proportional to μ 0 H ext .…”

“…Here, we focus on micrometer-sized permalloy (Fe 21.5 Ni 78.5 , Py) chiral structures-Py chiral metamolecules [7,8]. In our previous report [8], Py chiral metamolecules were fabricated using strain-driven self-coiling [9,10].…”

“…In our previous report [8], Py chiral metamolecules were fabricated using strain-driven self-coiling [9,10]. Ferromagnetic resonance (FMR) was studied using a cavity and a coplanar waveguide (CPW).…”