Crystal Structure and Low-Temperature Magnetic Ordering in Rare Earth Iron Germanates RFeGe2O7, R = Y, Pr, Dy, Tm, and Yb

Abstract

Polycrystalline samples of iron and rare earth germanates, RFeGe2O7 (R = Y, Pr, Dy, Tm, and Yb), have been prepared. Depending on the size of R, they present two different monoclinic crystal structures, described either in space group P21/c (no. 14) for R = Pr or in P21/m (no. 11) for the smaller rare earths R = Y, Dy, Tm, and Yb. The results of crystal structure refinements from room-temperature high-resolution neutron powder diffraction (NPD) data are given. Magnetization measurements between 350 and 1.6 K reveal the existence of one maximum, at 3 or 38 K for the praseodymium or yttrium germanate, respectively, and two separate anomalies for the remaining materials, which appear at T1 and T2 (T2 < T1), where T1 ≈ 40 K and T2 = 24, 6, and 5 K, for R = Dy, Tm, and Yb, respectively, indicating transitions to antiferromagnetically (AF) ordered states. Judging from low-temperature NPD data, three-dimensional (3D) AF ordering is established for all compounds, with simultaneous ordering of the R3+ and (or) Fe3...