Fundamental Mechanisms of Ultra-Low Loss Magnon Dynamics in Vanadium Tetracyanoethylene

Magnons are receiving interest in quantum information science because they can interact with point defects as well as coherently couple to spins, photons, and phonons. Highly coherent magnons require a low-loss magnetic material, such as the molecule-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]_x, x~2). The best V[TCNE]_x thin films grown using chemical vapor deposition (CVD) demonstrate ultra-low Gilbert damping α = (3.98 ± 0.22) × 10^-5 at room-temperature. Low damping in V[TCNE]_x persists at cryogenic temperatures, with linewidths at 5K comparable to room temperature (2 G at 9.4 GHz). Furthermore, V[TCNE]_x can easily be patterned using established e-beam lithography and liftoff techniques and incorporated into devices while maintaining low damping. Realizing the full potential of V[TCNE]_x for quantum information science requires a deeper understanding of the relationship between the coordination compound structure and the magnetic properties.<br/><br/>This talk will discuss recent studies on the microscopic structural changes that lead to an increase in magnetic damping as V[TCNE]_x ages. This deeper understanding informs a new generation of CVD growth. For example, Raman spectroscopy reveals that as V[TCNE]_x ages and oxidizes, structural changes in chemical bonds correlates with a suppression of magnetic order [1]. A parallel study uses electron energy-loss spectroscopy to validate the changes in bonding and in the vanadium coordination as V[TCNE]_x ages [2]. These advances in understanding the structure-function relationship have offered insight to the design of a new furnace for CVD growth of V[TCNE]_x.<br/><br/>[1] H. F. H. Cheung <i>et al. </i>J. Phys. Chem. C <b>2021 </b><i>125</i> (37), 20380-20388. https://doi.org/10.1021/acs.jpcc.1c04582<br/><br/>[2] Personal communication; A. Trout <i>et al.</i> Microsc. Microanal. 2020, 26, 3112−3114.