Magnetic order in the rare-earth ferroborate CeFe3(BO3)4

We have studied the magnetic order of the rare-earth ferroborate CeFe3(BO3)(4) through the thermodynamic and the neutron diffraction measurements. The heat capacity and the magnetic susceptibility revealed antiferromagnetic magnetic ordering at 29 K. In the neutron powder diffraction data, we observed the magnetic Bragg peaks indexed by the commensurate (CM) propagation vector k(CM) = (0, 0, 3/2) and the incommensurate (ICM) vector k(ICM) = (0, 0, 3/2+delta). The incommensurability delta increases with decreasing the temperature, and is evaluated to be 0.04556(16) at 3.7 K. Magnetic structure analysis reveals that the magnetic moments aligning in the ab plane form the collinear antiferromagnetic structure having k(CM)( )and helical structure having k(ICM). Detailed measurements of the magnetic susceptibility exhibit an additional anomaly at 27 K. Furthermore, the temperature dependence of the neutron diffraction profile on the single-crystal sample shows that the ICM and CM ordering occurs at 29 and 26 K, respectively. These results suggest a phase separation state between the collinear and helical structures. The multiferroicity of CeFe3(BO3)(4) is discussed on the basis of the determined magnetic structure.