Determination of the magnetic structure of SmFe3(BO3)4 by neutron diffraction: comparison with other RFe3(BO3)4 iron borates.

Temperature dependent neutron diffraction studies were performed on SmFe(3)(BO(3))(4). The crystallographic structure was determined to stay as R32 over the whole studied temperature range of 2 K < T < 300 K. A magnetic phase transition characterized by the magnetic propagation vector κ = [0 0 3/2] takes place at T(N) = 34 K. The magnetic structure sees an easy-plane arrangement within the trigonal basal a-b-plane of ferromagnetic layers of iron and samarium having a canting angle of about 70° relative to each other. Neighbouring layers in the c-direction are antiferromagnetically coupled; at 2 K the magnetic moment values amount to µ(Fe ) = 4.2(1) µ(B ) and µ(Sm) = 0.8(2) µ(B). The non-Brillouin type increase of the iron magnetic moment below T(N) points to a strong Fe-Sm exchange and to the simultaneous appearance of long range magnetic order on both sublattices.

Magnetic structure in iron borates RFe(3)(BO(3))(4) (R = Er, Pr): a neutron diffraction and magnetization study.

Neutron diffraction, susceptibility and magnetization measurements (for R = Er only) were performed on iron borates RFe(3)(BO(3))(4) (R = Pr, Er) to investigate details of the crystallographic structure, the low temperature magnetic structures and transitions and to study the role of the rare earth anisotropy. PrFe(3)(BO(3))(4), which crystallizes in the spacegroup R32, becomes antiferromagnetic at T(N) = 32 K, with τ = [0 0 3/2], while ErFe(3)(BO(3))(4), which keeps the P3(1)21 symmetry over the whole studied temperature range 1.5 K < T < 520 K, becomes antiferromagnetic below T(N) = 40 K, with τ = [0 0 1/2]. Both magnetic propagation vectors lead to a doubling of the crystallographic unit cell in the c-direction. Due to the strong polarization of the Fe-sublattice, the magnetic ordering of the rare earth sublattices appears simultaneously at T(N). The moment directions are determined by the rare earth anisotropy: easy-axis along c for PrFe(3)(BO(3))(4) and easy-plane a-b for ErFe(3)(BO(3))(4). There are no spin reorientations present in either of the two compounds but there is the appearance below 10 K of a minority phase in the Er-compound adopting a 120° arrangement of the Er-moments.

Magnetic order in FeCr(2)S(4)-type chalcogenide spinels.

The thiospinels of composition FeCr(2)S(4) and Fe(1+x)Cr(2-2x)Sn(x)S(4) with 0