X ray magnetic circular dichroism study of the magnetic anisotropy on TbMnO3

The magnetic anisotropy of TbMnO3 was explored by means of polarized x ray absorption spectroscopy and x ray magnetic circular dichroism XMCD measurements at the MnL2,3 and TbM4,5 edges as a function of temperature and magnetic field intensity. The selective magnetometry measurements were compared with the macroscopic magnetic properties on single crystals. XMCD measurements at the TbM4,5 edge as a function of the magnetic field reproduces quite well the macroscopic magnetic anisotropy at low temperatures with the Tb moments staying confined along their Ising axis within the ab plane, whereas a weak XMCD signal is observed at the MnL2,3 edge. These results point out that Tb3 single ion anisotropy is the only responsible for the magnetic anisotropy on this multiferroic compound at high magnetic fields. Moreover, we found MnL2,3 XMCD measurements show that the cycloidal antiferromagnetic order is almost unaffected by the applied magnetic field at low temperatures under an applied magnetic field. Therefore, we discuss that this strong Ising nature of Tb3 ions, through a magnetocrystalline coupling mediated by the oxygen atoms, must play an important role in the field induced electric polarization flop and therefore in the magnetoelectric coupling on TbMnO