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