Slow Relaxation of Magnetization in the Cobalt-Containing Strontium Hydroxy/Fluoro-Apatite

Strontium phosphates with apatite structure containing cobalt and fluoride atoms in the trigonal channels were synthesized and characterized by magnetic measurements. The compounds exhibit slow magnetization relaxation with two types of relaxing centers with an energy barrier for magnetization reversal of about 55 and 200 cm^–1, respectively. On the fluoride incorporation, the nature of the magnetic centers remains the same as in the initial hydroxyapatite, while the quantity of cobalt incorporated in the channels is reduced substantially. In the sample with the highest fluoride content slow relaxation behaviour almost disappears.