Direct detection of multiple backward volume modes in yttrium iron garnet at micron scale wavelengths

Using a set of wave-vector-specific multielement antennas, we have characterized the dispersion of spin waves in an yttrium iron garnet film at submicron lengths and resolved the dispersion relations of multiple backward volume modes, particularly in the region of their minima. The techniques developed now facilitate the characterization of spin waves at length scales limited only by available lithography and at a spectral resolution that generally exceeds that of Brillouin scattering. The data obtained are in excellent agreement with theoretical predictions based on a model Hamiltonian.

Figure 1

SEM images at the same magnification of the multielement antennas on a YIG film with periods of (a) 0.6 μm, (b) 1 μm, (c) 3 μm, and (d) 10 μm.

Figure 2

A schematic of the FMR measurement system. A 200-μm-thick glass cover slip creates a gap between the YIG film and the Cu base plate of the sample holder to avoid any effects from an adjacent conducting surface.

Figure 3

An example of raw data generated from a 10-μm period antenna. There are three classes of signals. The first, which is off scale, arises from the uniform precession mode (FMR), the second is caused by the three lowest-lying BV modes having an in-plane wavelength of 10 μm, and the last is from the corresponding three BV spin waves with an in-plane wavelength of 3.3 μm generated from the first odd spatial subharmonic $\left(n=3\right)$ of the antenna.

Figure 4

The measured frequencies of the lowest-lying, and the first few exchange split, backward volume spin waves in a 2.84-μm-thick YIG film at wavelengths of 10, 3, 1, and 0.6 μm. Shown also are the microscopic calculations involving the model spin Hamiltonian (black solid line) together with an approximate treatment based on a Fourier expansion of the magnetostatic Landau-Lifshitz equation (red dashed line). (a) shows the comparison using a modified internal field while (b) shows that for a modified saturation magnetization. Also shown is an approximate treatment due to Kreisel et al. [7] (green dot-dashed line). Finally, the points on the line designated $E_0$ correspond to the $k=0$ (uniform) FMR mode.