Magnetic properties of nickel halide hydrates including deuteration effects

Abstract Magnetic measurements on variously hydrated nickel chlorides and bromides, including deuterated forms, are reported. Results include locations and sizes of susceptibility maxima, T max and χ max , ordering temperatures T c , Curie constants and Weiss theta in the paramagnetic regime, and primary and secondary exchange interactions from analysis of low temperature data. For the latter a 2D Heisenberg model augmented by interlayer exchange in a mean-field approximation is applied. Magnetization data to 16 kG as a function of temperature show curvature and hysteresis characteristics quite system dependent. For four materials high field magnetization data to 70 kG at 2.00 K are also obtained. Comparison is made with theoretical relations for spin-1 models. Trends are apparent, primarily that T max of each bromide hydrate is less than for the corresponding chloride, and that for a given halide n D 2 O ( n =1 or 2) deuterates exhibit lesser T max than do nH 2 O hydrates. A monoclinic unit cell determined from powder X-ray diffraction data on NiBr 2 ·2D 2 O is different from and slightly larger than that of NiBr 2 ·2H 2 O. This provides some rationale for the difference in magnetic properties between these.