ИСТИНА

In present work the high pressure evolution of structural and magnetic properties of La0.75Ca0.25MnO3 was studied by means of X-ray diffraction up to 39 GPa and neutron diffraction up to 7.5 GPa. At normal pressure and temperature below TC = 240 K, a ferromagnetic state (FM) is exist in La0.75Ca0.25MnO3. The magnetic order in La0.75Ca0.25MnO3 undergoes a continuous transition from the ferromagnetic metallic ground state to the A-type antiferromagnetic (AFM) state of assumedly 2D pseudo-metallic character under pressure, that starts at about ~1 GPa and extends possibly to 20-30 GPa. The initial FM metallic ground state becomes unstable under high pressure due to strongly anisotropic distortions of MnO6 octahedra, and A-type AFM ground state with an eg orbital polarization of the dx2-z2 kind is gradually developed instead. The subsequent application of high pressure leads to the Pnma – Imma structural phase transformation in La0.75Ca0.25MnO3, mediated by a change in the octahedral tilting and anisotropic lattice compression, coupled to orbital ordering effects.