Magnetic properties of hexagonal RbNiF₃ with substituted ions

Abstract

Transparent RbNiF3 is analyzed in terms of ferrimagnetic spin ordering. It has the hexagonal BaTiO3 structure and the magnetic ion (Ni2+) is located in the center of fluoride octahedra on two nonequivalent sites. We have replaced nickel in the hexagonal structure with both nonmagnetic and magnetic ions [Ca, Cd, Mg, Co, and Mn] to further elucidate the magnetic structure. In the substitution of Mg for Ni there is a small preference of a sites and the solid solution retains ferrimagnietc order up to RbNi1/3Mg2/3F3. Calcium substituted for nickel has a strong preference for a-sites probably because it is larger and prefers a site with higher local cubic symmetry. Because of the a-site preference the moment increases from 21 emu/g for pure RbNiF3 to 27 emu/g for RbNi3/4Ca1/4F3. At 1/3 Ca, magnetic ordering has disappeared, consistent with the absence of magnetic ions on a sites. The only ion which completely replaced rubidium while retaining the hexagonal structure is Tl+. TlNiF3 is also ferrimagnetic with T C = 129°K and σ = 13 emu/g. Alhough our results are consistent with a ferrimagnetic model, recent neutron-diffraction results [S. J. Pickart and H. A. Alperin, J. Appl. Phys. 39, 1332 (1968).] indicate the possibility of a canted arrangement. © 1968 The American Institute of Physics.