The organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x∼2) has demonstrated potential for use in both microwave electronics and spintronics due to the combination of high temperature magnetic ordering (TC > 600 K), extremely sharp ferromagnetic resonance (peak to peak linewidth of 1 G), and low-temperature conformal deposition via chemical vapor deposition (deposition temperature of 50 °C). However, air-sensitivity leads to the complete degradation of the films within 2 h under ambient conditions, with noticeable degradation occurring within 30 min. Here, we demonstrate encapsulation of V[TCNE]x∼2 thin films using a UV-cured epoxy that increases film lifetime to over 710 h (30 days) as measured by the remanent magnetization. The saturation magnetization and Curie temperature decay more slowly than the remanence, and the coercivity is unchanged after 340 h (14 days) of air exposure. Fourier transform infrared spectroscopy indicates that the epoxy does not react with the film, and magnetometry measurements show that the presence of the epoxy does not degrade the magnetic properties. This encapsulation strategy directly enables a host of experimental protocols and investigations not previously feasible for air-sensitive samples and lays the foundation for the development of practical applications for this promising organic-based magnetic material.

We experimentally demonstrate high quality factor spin wave resonances in an encapsulated thin film of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]~2) coated on an a-plane sapphire substrate by low temperature chemical vapor deposition. The thickness standing wave modes are observed in a broad frequency range (1 GHz ~ 5 GHz) with high quality factor exceeding 3,200 in ambient air at room temperature, rivaling those of inorganic magnetic materials. The exchange constant of V[TCNE]~2 , a crucial material parameter for future study and device design of the V[TCNE]~2, is extracted from the measurement with a value of (4.61 ± 0.35) × 10 −16 m 2 . Our result establishes the feasibility of using organic-based materials for building hybrid magnonic devices and circuits.Spin waves, which are the collective excitation of the magnetization in magnetic materials, have been attracting intensive attention recently due to potential applications in both fundamental research 1-4 and device applications 5-9 thanks to properties such as being ohmic loss free, 10,11 long spin lifetime, and large-bandwidth tunability. In particular, yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) has been long considered as one of the most attractive magnon media, thanks to its magnetic, microwave, mechanical and optical properties. As a result, YIG has been widely adopted to investigate the interactions among spin waves, microwaves 12 -19 , acoustic waves 20,21 and optical excitations. [22][23][24][25][26] However, high quality YIG films can only been grown on specific lattice-matched substrates such as gadolinium gallium garnet (GGG,