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