Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE]_x

Here we present a detailed and systematic study of the low-temperature magnetic resonance properties of the molecule-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x). We observe resonance linewidths at 5 K consistent with a quality factor of 8,200, comparable to room-temperature values. This is consistent with scattering from two-level fluctuators (TLFs), and is expected to lead to further narrowing at temperatures in the milli-Kelvin range due to freeze-out of thermal magnons. These results are notable because they position V[TCNE]x as a viable candidate, competitive with YIG, for low-temperature microwave applications in quantum information science and technology. The viability of V[TCNE]x as a quantum-information-relevant material is also enhanced by the ease of deposition and patterned fabrication afforded by our room-temperature chemical vapor deposition (CVD) system, which allows for facile and versatile on-chip integration of V[TCNE]x with pre-patterned microwave circuits.