Antiferromagnetism in a mixed-valence iron fluoride heptahydrate (Fe2F5⋅7H2O) and related compounds

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Abstract
Magnetic susceptibilities of mixed metal fluorides of the type Fe(III)M(II)F5⋅7H2O, where M=Fe, Co, Ni, or Zn, were measured from 2.3 to 295 °K with a vibrating-sample magnetometer at an applied field of 10 kOe. Antiferromagnetic transitions were observed in Fe2F5⋅7H2O, TN=3.0±0.2 °K, and in FeCoF5⋅7H2O, TN=3.42±0.10 °K. Deviation from Curie–Weiss behavior was observed in FeNiF5⋅7H2O at temperatures below 10 °K suggesting a possible ordering at temperatures below 2.3 °K, the lowest temperature obtained in this experiment. FeZnF5⋅7H2O and the related compound Al(III)Fe(II)F5⋅7H2O were paramagnetic down to 2.3 °K while FeF2⋅4H2O became antiferromagnetic at 3.4±0.15 °K.