Spin-wave confinement and coupling in organic-based magnetic nanostructures

Abstract

Vanadium tetracyanoethylene (V[TCNE]x) is an organic-based ferrimagnet that exhibits robust magnetic ordering (TC of over 600 K), high quality-factor (high-Q) microwave resonance (Q up to 3500), and compatibility with a wide variety of substrates and encapsulation technologies. Here, we substantially expand the potential scope and impact of this emerging material by demonstrating the ability to produce engineered nanostructures with tailored magnetic anisotropy that serve as a platform for the exploration of cavity magnonics, revealing strongly coupled quantum confined standing wave modes that can be tuned into and out of resonance with an applied magnetic field. Specifically, time-domain micromagnetic simulations of these nanostructures faithfully reproduce the experimentally measured spectra, including the quasiuniform mode and higher-order spin-wave (magnon) modes. Finally, when the two dominant magnon modes present in the spectra are brought into resonance by varying the orientation of the in-plane magnetic field, we observe anticrossing behavior, indicating strong coherent coupling between these two magnon modes at room temperature. These results position V[TCNE]x as a leading candidate for the development of coherent magnonics, with potential applications ranging from microwave electronics to quantum information.

Low-damping ferromagnetic resonance in electron-beam patterned, high-Q vanadium tetracyanoethylene magnon cavities

“…The magnitude of this crystal field is consistent with previous measurements of V [TCNE] x templated nanowires. 22 In addition to being selfconsistent, these results also predict the anisotropy curves for the disks (blue lines in Fig. 3(d)).…”

“…18,19 These relatively benign deposition conditions allow for depo-sition on a wide variety of substrates and pre-patterned circuits, positioning V[TCNE] x as an exciting option for on-chip magnetic and magnonic device incorporation. [20][21][22] However, realizing this promise has been limited by the lack of techniques for patterning V [TCNE] x films at micron to sub-micron length scales.…”

“…These results suggest the crystal-field contribution arises from anisotropic relaxation in the patterned bars, which corroborates prior work with V[TCNE] x nanowires where an additional in-plane crystal field is reported due to anisotropy in the relaxation of the templated structures. 22 The more complicated spectra of the disks suggests that the disks are acting as spin-wave cavities with complex internal mode structure, Fig. 3(e).…”

Raman Spectroscopy and Aging of the Low-Loss Ferrimagnet Vanadium Tetracyanoethylene

“…where γ is the gyromagnetic ratio, H is the external magnetic field, θ is the angle of the external field with respect to the film normal, H ef f = 4πM ef f = 4πM s − H k , which is a combination of the saturation magnetization and the anisotropy field. One possible origin of the anisotropy field is from strain due to differential thermal expansion of V [TCNE] x and the underlying substrate [29,30]. In figure 5, we show a field-modulated FMR signal measured at 3 GHz.…”

Spin Wave Excitation, Detection, and Utilization in the Organic‐Based Magnet, V(TCNE)x (TCNE = Tetracyanoethylene)

“…[ 26,27 ] Various spin wave modes with high quality factors have been observed by spatial confinement of V(TCNE) x films. [ 28 ] The spin current carried by magnons in V(TCNE) x possesses a long lifetime and low Gilbert damping, and can be converted into an electrical current in an adjacent Pt layer by the ISHE. [ 14 ]…”