Observation of quasi-universal magnetic behavior in a random exchange Heisenberg antiferromagnetic chain: Neutron irradiated quinolinium (TCNQ)2

Low field electron spin resonance measurements of the magnetic susceptibility (χ) and absorption linewidth over the temperature range 0.04 – 300 K are reported for quinolinium (TCNQ)₂ into which increased amounts of disorder have been introduced by fast neutron irradiation. It is found that below 20 K, χ = AT^-α; A increases linearly with the irradiation dose, but $\text{α (? 0.8)}$ is almost independent of it, in agreement with the quasi universal behavior predicted by recent renormalization calculations for a random exchange Heisenberg antiferromagnetic chain. Measurements of the g-shift at 4.2 K range indicate that all of χ is associated with TCNQ chains. These results are discussed in terms of the renormalization calculation of Soos and Bondeson.