Large isotropic shifts of the g-value in the ESR spectrum of Fe(III) as an impurity in a sample of ferrous spin-crossover complex (tetrakis(2-pyridylmethyl)ethylenediamine)iron(II)perchlorate in the range 4-370 K were detected as a function of temperature. New antiferromagnetic phase at T < 20 K was discovered using SQUID magnetometer.
Lazarev, G., Ersez, T., Lara, F., & Moreno-Espara, R. (1998). Observation of Anomalous g-value Temperature Dependence of the ESR Spectrum of Fe(III). Applied Magnetic Resonance, 14(1), 19-24. https://doi.org/10.1007/BF03162003