Magnetic and structural properties of Fe-doped layered cobaltite TbBaCo_1.91Fe_0.09O_5.5 at high pressures

The crystal and magnetic structures of the perovskite-like, oxygen deficient layered cobalt oxide TbBaCo1.91Fe0.09O5.5 have been studied by means of neutron diffraction at high pressures up to 6.2 GPa in the temperature range 5-300 K and X-ray diffraction at high pressures up to 30 GPa and ambient temperature. The structural anomalies in lattice compression at P=20-25 GPa were revealed, which could be associated with the insulator-metal transition. At ambient pressure below T-N=300 K a formation of the complex magnetic structure on the Co/Fe sublattice, comprising the G-type antiferromagnetic (AFM) and ferromagnetic (FM) components, was observed. Below T approximate to 150 K the FM component vanished. At T=5 K a presence of the long range AFM order on the Tb sublattice was also revealed. At high pressures, the FM component has become suppressed and the only G-type AFM order was found for the Co/Fe sublattice. The Neel temperature decreased noticeably down to 275 K at P=6.2 GPa with a pressure coefficient dT(N)/dP=-4 K/GPa. The intrinsic mechanisms of the observed pressure-induced magnetic phenomena are discussed.