Low temperature, high magnetic field investigations of the nature of magnetism in the molecular semiconductor β- cobalt phthalocyanine (C32H16CoN8)

Results from detailed investigations of the magnetic properties of a powder sample of beta-CoPc for the temperatures T=0.4 K to 300 K and in magnetic fields H up to 90 kOe are reported. X-ray diffraction confirmed the beta-phase and scanning electron microscopy showed plate-like morphology of the sample. For T > 3 K, the data of magnetic susceptibility chi vs. T fit the Curie-Weiss (CW) law yielding 0 = -2.5 K,mu = 2.16 mu(B) per Co2+ and g=2.49 for spin S=1/2 of the low spin-state of Co2+ However for T < 3 K, they vs. T data deviates from the CW law yielding a peak in chi at T-max = 1.9 K. It is shown that they vs. T data from 0.4 K to 300 K fits well with the predictions of the Bonner-Fisher (BF) model for S=1/2 Heisenberg linear chain antiferromagnet with the Co2+-Co2+ exchange J/kB = 1.5 K (<(H)over cap> = 2J Sigma S-i center dot Si+1). The data of magnetization M vs. H at T=1 K agrees with the predictions of the BF model with J/k(B) = 1.5 K, yielding saturation magnetization M-s =12.16 emu/g above 60 kOe corresponding to complete alignment of the spins. (C) 2016 Elsevier B.V. All rights reserved.