Hidden magnetic instability in the substituted multiferroics (Nd,Tb)Fe3(BO3)4

Golosovsky, I.V., Mukhin, A.A., Skumryev, V., (...), Ivanov, V.Y., Gudim, I.A.// Physical Review B//


In the substituted Nd1xTbxFe3(BO3)4 (x=0.1 and x=0.2), possessing almost easy-axis magnetic structure at low temperatures, an unusual two-step transition in fields along the trigonal c axis was observed by magnetization and single-crystal neutron diffraction studies. At the first step, only part of the Tb Ising-type moments flip to the c axis, which is accompanied by a significant deviation of the antiferromagnetic Fe spins from the c axis. At the second step, the remaining Tb moments flip and the Fe moments flop into the basal plane. The ob- served evolution is qualitatively explained by a model assuming small deviations of Tb moments from the trigonal axis due to local environment distortions, which leads to nonequivalence of the Tb ions with respect to effective Tb-Fe exchange and external field. Thus, an intrinsic “hidden” instability of the magnetic system in the magnetic field occurs.