High pressure effects on the magnetic and crystal structure of La0.75Ba0.25CoO3

• External pressure suppresses ferromagnetic state.
• Structure is described by two-phase model.
• Pressure induces spin state crossover of the Co ions.

The crystal and magnetic structure of the La0.75Ba0.25CoO3 has been studied as a function of temperature and high pressure up to 8 GPa using neutron powder diffraction. The crystal structure of the compound at room temperature is considered to be single phase rhombohedral (space group R  3−c), at T = 50 K the crystal structure is described by two-phase model assuming the coexistence of the orthorhombic (Imma) and rhombohedral (R  3−c) phases. The magnetic structure is found to be ferromagnetic with Curie temperature about 200 K and magnetic moment 1.6 μB per Co ion. Applied external pressure strongly reduces magnetic moment, it decreases down to 0.7 μB/Co at pressure of 8 GPa. The drop of magnetic moment is associated with a pressure-driven spin state crossover of the cobalt ions from the intermediate spin state to the low spin state.