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Organic-Based Magnets: New Materials, New Phenomena, And New Applications – Art Epstein

Date: Thu. April 22nd, 2004, 4:15 pm-5:15 pm
Location: Rockefeller 301

Magnets utilizing organic groups with essential spin have been reported since the mid-1980s. Though initial organic-based magnets (OBMs) had magnetic ordering temperatures (Tc’s) below 5K, OBMs now have Tc’s up to 400K. The chemical control of OBMs will be introduced. In addition to magnetic phenomena already known for conventional transition metal and rare earth magnets, OBMs feature unique phenomena enabled by the shape and internal electronic structure of the organic molecules. Examples are illustrated with experimental results for magnets based on tetracyanethylene, [TCNE], which as an anion has spin ¸. For example, application of blue light to Mn++[TCNE]-2 increases the magnetic susceptibility below the Tc of 75 K and green light reverses the effect. This phenomenon is due to optical absorption of TCNE]- followed by photo-reversible structural changes.[1] V++[TCNE]-2 and related materials are magnetic organic semiconductors (room temperature resistivity similar to silicon, ~ 104 ohm-cm) with Tc’s up to 400 K. Films are prepared from low temperature CVD.[2] M(H,T) and coercive field are controlled by chemical composition. Magnetoresistance to 32 tesla s upports that V[TCNE]2 is a “half-semiconductor” with fully spin polarized valence and conduction bands. The possible roles and advantages of OBMs and other nonmagnetic organic-based materials such as carbon nanotubes in technologies such as spintronics will be discussed.Ê [1] D.A. Pejakovic, et al, Phys. Rev. Lett. 88, 057202/1 (2002). [2] K.I. Pokhodnya, et al, Adv. Mater. 12, 410 (2000). [3] V.N. Prigodin, et al., Adv. Mater. 14, 1230 (2002). Supported by U.S. DOE, DARPA, ARO, and AFOSR.

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