SYNTHESIS, STRUCTURE, AND MAGNETIC-PROPERTIES OF CAMSI(2)O(6) (M=CO,NI) COMPOUNDS AND THEIR SOLID-SOLUTIONS

The title compounds have been synthesized using a sol-gel route from c alcium and transition metal nitrates and tetraethylorthosilicate. A si lica excess was used to avoid the formation of parasitic phases. These materials exhibit the clinopyroxene structure where the transition me tal build MO(6) octahedra from infinite zigzag chains running in the c axis direction, Magnetic and specific heat measurements demonstrate t he existence of ferromagnetic interactions inside the MO(6) zigzag cha ins that order antiferromagnetically below T-N = 9.75 and 20.2 K for M = Co and Ni, respectively. Neutron powder diffraction data allow the determination of the magnitude, m(0) = 3.30 +/- 0.15 mu(B), and orient ation, angle of 41 degrees with the a axis, of the magnetic moments in side the structure. (C) 1996 Academic Press, Inc.