Electron spin resonance measurements of the spin Hamiltonian zero-field splitting parameter D as a function of temperature for trigonally distorted Cr3+⋅6H2O magnetic complexes in families of hydrated crystals. I

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Abstract
The spin Hamiltonian zero‐field splitting parameter D is measured as a function of temperature for trigonally distorted Cr3+⋅6H2O magnetic complexes in families of hydrated crystals. The purpose of the study is to classify the isomorphs of the crystals via their magnetic behavior so that use can be made of similarities and differences between the members when analyzing data obtained from electron–nuclear double resonance (ENDOR) measurements. The D vs T curves are found to form well ordered patterns within a family of isomorphs, and the patterns are significantly different for each type of crystal. When the straight line part of the curves between 195 and 297 °K are extrapolated to high temperature, the existence of common crossing points is found. The orderly nature of the patterns is expected to provide an additional aid in describing the physical behavior of the crystals. The crystals studied are alums, guanidinium aluminum sulfate hexahydrate (GAlSH) and its isomorphs, and aluminum chloride hexahydrate (AlCl3⋅6H20). The Cr3+ ion is doped as a small impurity in most of the crystals but some concentrated crystals are also studied. Electron spin resonance measurements are made at X‐band microwave frequencies (∼9.4 GHz) at the four temperatures 4.2, 77, 195, and 297 °K whenever possible.