Spin Dynamics in Disordered TCNQ Salts

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Abstract
A segment model with c ∼ 0.10 weak exchanges among 1-c strong exchanges accounts for the static thermodynamics of several structurally disordered, complex TCNQ salts. The segment model is extended to the spin dynamics of random-exchange Heisenberg antiferromagnetic chains (REHACs), as probed by magnetic resonance. The exchange-narrowed epr linewidth and resonance shifts at ultralow temperature are related to dipolar interactions among spins delocalized on parallel odd-length segments. REHACs display a wide variety of exchange fields and are thermally decoupled into finite domains. An inhomogeneous superposition of such finite domains is probed in magnetic resonance experiments.