Emergence of Ferromagnetism in TbMnO $_{3}$ Bulk by Al-Doping

Polycrystalline Tb_1-xAl_xMnO₃ ( x=0, 0.05, 0.07, 0.1, 0.2, and 0.3) were synthesized by standard solid-state reaction. The starting precursors Tb₄O₇, MnO₂, Al₂O₃ were stoichiometric mixed and calcined at 1200 °C for 12 hours in air atmosphere. The structural properties of the samples were investigated by X-ray diffraction (XRD) in standard θ-2θ configuration. The broadening and displacement of the peaks in the XRD diffractograms suggests that the Al doping leads to a distortion of the orthorhombic unit cell of the antiferromagnetic TbMnO₃. Careful temperature- and field-dependent magnetic measurements by means of SQUID magnetometry show antiferromagnetic and weak ferromagnetic behavior of the undoped and Al-doped TbMnO₃ samples, respectively. Probably, the ferromagnetic response correlates with the unit cell deformation. The results obtained were compared with those achieved in Tb_0.7Al_0.3MnO₃ thin films which were deposited in SrTiO₃ and MgO substrates by rf sputtering technique. Due to the close relationship between magnetic order and ferroelectricity in TbMnO₃, these results may provide a novel route to induce magnetoelectric coupling and tailor their ferroelectric response.