MAGNETIC-STRUCTURE OF THE ORTHOSILICATES MN2SIO4 AND CO2SIO4

The antiferromagnetic structure of the orthosilicates Mn2SiO4 (tephroite) and Co2SiO4 was determined by neutron diffraction. In Mn2SiO4 the magnetic moments on the crystallographic M2-site are aligned almost parallel to the a-axis (space group Pnma). On the MI-site the spin arrangement is collinear and nearly parallel to a below TN=47.1(1) K but pronounced canting away from the crystallographic axes is confirmed below about 20 K. The magnetic moments are different at all temperatures below T4-N$/ with smaller moments on M1, and at 2K both moments are smaller than the spin-only value of 5μB. In Co2SiO4 the moments on M2 are parallel to the b-axis whereas on M1 they are canted for the whole temperature range below the transition temperature (TN=49.5(1) K) in contrast to results from earlier neutron powder diffraction measurements. The magnetic moments are only slightly different and exceed the spin-only value as a result of orbital contribution.