Howard Yu

Ultra-narrow ferromagnetic resonance in organic-based thin films grown via low temperature chemical vapor deposition

We present the growth of thin films of the organic-based ferrimagnetic semiconductor V[TCNE]x (x ∼ 2, TCNE: tetracyanoethylene) via chemical vapor deposition. Under optimized growth conditions, we observe a significant increase in magnetic homogeneity, as evidenced by a Curie temperature above 600 K and sharp magnetization switching. Further, ferromagnetic resonance studies reveal a single resonance with full width at half maximum linewidth of 1.4 G, comparable to the narrowest lines measured in inorganic magnetic materials and in contrast to previous studies that showed multiple resonance features. These characteristics are promising for the development of high frequency electronic devices that take advantage of the unique properties of this organic-based material, such as the potential for low cost synthesis combined with low temperature and conformal deposition on a wide variety of substrates.

Thin‐Film Deposition of an Organic Magnet Based on Vanadium Methyl Tricyanoethylenecarboxylate

The preparation and characterization of a new thin-film organic-based magnet V[MeTCEC]x (V = vanadium; MeTCEC = methyl tricaynoethylenecarboxylate) via low-temperature chemical vapor deposition (50 °C) is reported. These thin films exhibit room-temperature magnetic ordering and semiconducting behavior, demonstrating the ability of tuning their magnetic, and potentially spintronic, functionality via chemical modification of the organic ligand.

Vanadium[ethyl tricyanoethylene carboxylate]x: a new organic-based magnet

We present the synthesis of a new high Curie temperature (Tc ∼ 145 K) organic-based magnet with composition V[ETCEC]1.3·0.3 CH2Cl2 formed by the reaction of ethyl tricyanoethylenecarboxylate (ETCEC) with V(CO)6 in CH2Cl2. Analysis of the IR spectrum indicates that all nitrile and carbonyl oxygen are coordinated to V(II) sites. Temperature-, field-, and frequency-dependent measurements of the magnetization reveal complex magnetic behavior with a magnetic transition into a more disordered state. Application of the random anisotropy model (RMA) shows that this disordered state is different from the correlated spin glass (CSG) phase observed in analogous organic-based magnets V[MeTCEC]x and V[TCNE]x synthesized in CH2Cl2. This suggests that V[ETCEC]x is less disordered than its analogues, which can be attributed to the slower reaction rate. This result provides a new partner to MeTCEC and TCNE based materials for the exploration of all-organic magnetic heterostructures.

Thin film synthesis of the organic-based magnet vanadium ethyl tricyanoethylenecarboxylate

We report the preparation and characterization of a new thin film organic-based magnet V[ETCEC]x, with TC of 161 ± 10 K, via low temperature chemical vapor deposition (CVD; T = 55 °C). X-ray photoelectron spectroscopy (XPS) indicates the ratio of V to ETCEC is 1:1.4. In addition, analysis of Fourier-transform infrared (FTIR) spectroscopy suggests a similar physical structure to V[ETCEC]x powder, with all nitrile and carbonyl oxygen coordinating to V(II) sites. Temperature-, field-, and frequency-dependent measurements of the magnetization as well as ferromagnetic resonance (FMR) measurements reveal complex magnetic behavior with a magnetic transition to a more disordered state at a freezing temperature just below the Curie temperature. The development of this magnetic thin film enables the direct incorporation of V[ETCEC]x into existing organic spintronics devices and opens up the potential exploration of all-organic magnetic heterostructures.

Thin-film encapsulation of the air-sensitive organic-based ferrimagnet vanadium tetracyanoethylene

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 m...

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at <60 °C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

Electrical transport in a hybrid organic/inorganic heterostructure

We report the electrical transport properties of a hybrid organic/inorganic diode device consisting of a layer of an organic ferrimagnetic semiconductor V[TCNE]x (x~2, TCNE: tetracyanoethylene; TC ~ 400 K, EG ~ 0.5 eV, σ~ 10-2 S/cm) and a GaAs/AlGaAs p-i-n diode. Comparison with a control excluding the V[TCNE]x~2 reveals that the addition of the V[TCNE]x~2 layer shifts the turn-on voltage and ideality of the diode in accordance with bulk V[TCNE]x~2 properties. This result has implications for the use of inorganic systems as probes of spin physics in organic and molecular systems.