Magnetic frustration, phase competition and the magneto-electric effect   in NdFe3(BO3)4
  We present an element selective resonant magnetic x-ray scattering study of NdFe3(BO3)4 as a function of temperature and applied magnetic field. Our measurements show that the magnetic order of the Nd sublattice is induced by the Fe spin order. When a magnetic field is applied parallel to the hexagonal basal plane, the helicoidal spin order is suppressed and a collinear ordering, where the moments are forced to align in a direction perpendicular to the applied magnetic field, is stabilized. This result excludes a non-collinear spin order as the origin of the magnetically induced electric polarization in this compound. Instead our data imply that magnetic frustration results in a phase competition, which is the origin of the magneto-electric response. 
J. E. Hamann-Borrero, S. Partzsch, S. Valencia, C. Mazzoli, J.   Herrero-Martin, R. Feyerherm, E. Dudzik, C. Hess, A. Vasili...
cond-mat.str-el cond-mat.mtrl-sci cond-mat.other