Magnetism of La0.625Sr0.375MnO3 under high pressure from first principles

The structural, electronic, and magnetic properties of rhombohedral La0.625Sr0.375MnO3 under high hydrostatic pressure are investigated from first-principles density-functional calculations. We employ three different levels of approach: the generalized-gradient approximation (GGA), the GGA+U, and the pseudo-self-interaction correction (PSIC). All methods coherently indicate an enhancement of antiferromagnetic coupling as compression is applied, i.e., contrary to naive expectations, double exchange is not enhanced but weakened as Mn-O distances shorten. This is due to the increasing electrostatic repulsion and electron localization. On the other hand, Jahn-Teller distortions are minimal and symmetry remains roughly rhombohedral even at high pressure, at variance with distortions induced by planar strain. GGA+U and PSIC predict no change in magnetization upon compression; plain GGA instead finds a large (20%) drop at high pressure. We conclude that this is an artifact due to the GGA underestimate of the minority-channel gap.