Rare-earth ferroborates RFe3(BO3)4

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Abstract
A brief review of the physical properties of the rare-earth ferroborate family R Fe 3 ( B O 3 ) 4 is given. At high temperatures some of these compounds exhibit a first-order structuralphase transition from the high-symmetry R 32 to the low-symmetry P 3 1 2 1 modification. The temperature of this transition decreases systematically with increasing radius of the rare-earth ion. All compounds of this family have antiferromagnetic ordering of the iron subsystem at low temperatures. The rare-earth subsystem, while remaining paramagnetic to the lowest temperatures, is magnetically biased by the magnetic field of the ordered iron subsystem. Although the antiferromagnetic transition temperature T N = 20 – 40 K depends weakly on the species of rare-earth ion, the orientation of the magnetic moments of the Fe 3 + ions in the ordered state is determined by the R 3 + ion. For example, in compounds with Y, Nd, Er, and Tm the magnetic moments of the iron are oriented in the a b plane, while in compounds with Tb and Dy they are parallel to the c axis. In Gd Fe 3 ( B O 3 ) 4 a first-order spin-reorientation phase transition is observed at T S R ∼ 9 K . It is found that Gd Fe 3 ( B O 3 ) 4 and Nd Fe 3 ( B O 3 ) 4 are multiferroics; this is manifested in magnetoelectric and magnetoelastic effects that are dependent on the orientation and magnitude of the external magnetic field.