Geometric magnetic frustration in olivines

Polycrystalline samples of Mn2SiO4, Mn2GeO4, Co2SiO4 and Ni2SiO4 were prepared and studied in the context of a search for geometrically frustrated magnetic materials. These compounds are isostructural with olivine, a series of minerals commonly found in the terrestrial crust. The olivine structure possesses a distinctive magnetic lattice in which metal ions sit at the vertices of corner-sharing triangles, forming alternating sawtooth chains. Magnetic susceptibility experiments reveal that the manganese-based olivines exhibit spin-glass transitions and magnetic frustration, while the cobalt olivine exhibits antiferromagnetic order with no suppression of the Neel temperature. The magnetic susceptibility of nickel olivine exhibits a large deviation from Curie-Weiss behavior, suggesting the presence of a magnetic structure in which a sublattice possessing a spin gap interacts with surrounding local-moment Ni2+ ions.