Geometric magnetic frustration in olivines

Polycrystalline samples of Mn2SiO4, Mn2GeO4, Co2SiO4 and Ni2SiO4 were prepa red and studied in the context of a search for geometrically frustrated mag netic materials. These compounds are isostructural with olivine, a series o f minerals commonly found in the terrestrial crust. The olivine structure p ossesses a distinctive magnetic lattice in which metal ions sit at the vert ices of corner-sharing triangles, forming alternating sawtooth chains. Magn etic susceptibility experiments reveal that the manganese-based olivines ex hibit spin-glass transitions and magnetic frustration, while the cobalt oli vine exhibits antiferromagnetic order with no suppression of the Neel tempe rature. The magnetic susceptibility of nickel olivine exhibits a large devi ation from Curie-Weiss behavior, suggesting the presence of a magnetic stru cture in which a sublattice possessing a spin gap interacts with surroundin g local-moment Ni2+ ions.