Neel temperatures of synthetic substituted goethites and their rapid determination using low-field susceptibility curves

The Neel temperatures (T-N) Of synthetic goethites (alpha-FeOOH), substitut ed with diamagnetic elements (Al, Ga) have been determined from the tempera ture dependence of their low-field susceptibility using a Kappabrige AC bri dge. These temperatures proved to be identical to those derived from more c onventional measurements of high-field or remanent magnetization versus tem perature, and in good agreement with those inferred from Mossbauer models. The low-field susceptibility based-technique appears to offer a precise and rapid method of determining T-N. While Neel temperature coincides with max imum unblocking temperature in Gagoethites, supporting the assumption that antiferromagnetism and parasitic ferromagnetism have a similar origin in go ethite, the lack of clear correlation between saturation remanent magnetiza tion and increasing diamagnetic substitution suggests that the weak ferroma gnetism of goethite is due to substitution independent defects induced duri ng crystal growth.