Magnetic structure in iron boratesRFe3(BO3)4 (R = Er, Pr): a neutron diffraction and magnetization study

Abstract

Neutron diffraction, susceptibility and magnetization measurements (forR = Er only) were performedon iron borates RFe3(BO3)4 (R = Pr, Er) to investigate details of the crystallographic structure, the low temperature magneticstructures and transitions and to study the role of the rare earth anisotropy.PrFe3(BO3)4, which crystallizes in thespacegroup R32, becomesantiferromagnetic at TN = 32 K, with τ = [0 0 3/2],while ErFe3(BO3)4, whichkeeps the P3121 symmetry over the whole studied temperature range1.5 K < T < 520 K, becomesantiferromagnetic below TN = 40 K, with τ = [0 0 1/2]. Both magnetic propagation vectors lead to a doubling of the crystallographic unit cell in thec-direction. Due to the strong polarization of the Fe-sublattice, themagnetic ordering of the rare earth sublattices appears simultaneously atTN. The moment directions are determined by the rare earth anisotropy: easy-axis alongc forPrFe3(BO3)4 andeasy-plane a–b for ErFe3(BO3)4. There are no spin reorientations present in either of the two compounds but there isthe appearance below 10 K of a minority phase in the Er-compound adopting a120° arrangement of the Er-moments.