Effect of high pressure on the crystal and magnetic structure and on the raman spectra in Pr0.7Ba0.3MnO3 manganite

Abstract

The crystal and magnetic structure and the Raman spectra in Pr0.7Ba0.3MnO3 manganite have been studied by the neutron diffraction technique at pressures up to 5 GPa as well as by the X-ray diffraction and Raman spectroscopy at pressures up to 30 GPa. The pressure dependence is determined for the lattice parameters, unit cell volume, Mn-O bond lengths in the orthorhombic structure of the Imma symmetry, and bending and stretching vibration modes for oxygen octahedra. In the low-temperature range at pressure P = 1.9 GPa, the magnetic transition from the initial ferromagnetic (FM) ground state (T C = 197 K) to the A-type antiferromagnetic (AFM) state (T N = 153 K) has been revealed. The FM and AFM phases coexist at pressures up to 5.1 GPa and exhibit negative and positive values of the pressure coefficient for the Curie and Neel temperature, respectively (dT C/dP = −2.3 K/GPa and dT N/dP = 8 K/GPa). The pressure dependence of the Curie temperature in Pr0.7Ba0.3MnO3 differs drastically from that observed in other manganites of nearly the same composition with the orthorhombic Pnma and rhombohedral \(R\bar 3c\) structures, where the FM phase is characterized by the positive values of dT C/dP. The structural mechanisms of these phenomena are discussed.