CORRELATION OF NEEL TEMPERATURE AND VACANCY DEFECTS IN FINE-PARTICLE GOETHITES

Positron annihilation lifetime spectroscopy (PALS) has been used to st udy the vacancy-type defects in fine-particle goethites (alpha-FeOOH). The PALS spectra reveal three components. The intermediate lifetime c omponent (tau(2), I-2) is attributed to positrons trapped at vacancy d efects. The relative intensity of the intermediate lifetime component, I-2, increases significantly with decreasing Neel temperature, and th is increase is attributed to increasing concentration of vacancy defec ts. These results support a model of magnetic ordering of clusters ari sing from a high concentration of iron vacancies which reduces the Nee l temperature in these fine-particle goethites.