Tetragonal to monoclinic transition in the metallic antiferromagnet Pr0.5Sr0.5MnO3

The structural changes associated with the ferromagnetic (FM)/metallic to antiferromagnetic (AFM)/insulating transition of Pr1/2Sr1/2MnO3 (I4/mcm-->P2(1)/n) are described in detail. Based on high-resolution neutron-diffraction data, in the P2(1)/n phase Mn1 and Mn2 octahedra have the same charge and are identically deformed. The electronically induced transition to the antiferromagnetic A-type structure at T-N is the result of a stretchinglike distortion of the octahedra that (i) contracts the Mn-O2 bond perpendicular to the FM planes by deviating beta from 90 degrees and (ii) injects electrons into Mn-O1 and Mn-O3 bonds. The observed microscopic changes are completely different to the structural transition in the A-type LaMnO3 and are discussed in the light of the orbital polarization previously proposed. [S0163-1829(99)51038-2].