Magnetic and Other Studies of a Reversible Phase Change in CoSiF6·6H2O

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Abstract
Magnetic, optical, and thermal expansion studies reveal a reversible phase transition in CoSiF6·6H2O at a temperature, Tc, which was found to be 246°±2°K during cooling and 259°±1°K during heating. This thermal hysteresis appears to be real as Tc is independent of the heating or cooling rate. The magnetic symmetry of the crystal is uniaxial above Tc but orthorhombic below it. The sharp change in color from pink to orange‐yellow at Tc is accompanied by spectral changes with the appearance of a new band, presumably indicating the effect of changes in the closed‐packed structure on the symmetry and shape of the Co(H2O)6 clusters. Crystals diluted with the similar zinc salt have an approximately uniaxial magnetic ellipsoid, a feeble anisotropy appearing in the ``symmetry'' plane at low temperatures. From these and the available resonance data the g values for the undiluted crystal have been estimated which resemble more closely those for a typical orthorhombic case than for a trigonal.

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