Magnetic susceptibility of sodium rare-earth fluorites Na0.5-xR0.5+xF2+2x (R = Dy, Ho, Er, Tm, Yb) and some ordered phases

Magnetic properties of the nonstoichiometric phases with the fluorite-type "defect" structure Na0.4R0.6F2.2 (R = Ho, Er, Tm, Yb) and Na0.35DY0.65F2.3 have been studied as well as some ordered phases with different distortions of the initial fluorite lattice (NaHo2F7, Na7Tm13F46, NaYb2F7, and Na7Yb13 F46) and Na1.5Dy1.5F6 with the gagarinite-type structure (NaCaYF6). Magneti c susceptibility chi was measured with the aid of the Faraday balance in th e temperature range from 20 to 300 K. The crystals with R = Dy, Ho, Er, Tm are paramagnetic; their temperature dependence chi is described by the Curi e-Weiss law. It is shown that in the temperature range studied, magnetic su sceptibility does not depend on the degree of order of Dy, Ho, Er, and Tm i ons in the structure. Below 80 K, the temperature dependence of magnetic su sceptibility of the the Yb3+- containing phases differs from the analogous dependence X of an ideal paramagnetic crystal, which is assumed to be cause d by the interaction of the crystalline field with Yb3+ ions. (C) 2001 MAIK "Nauka/Interperiodica".