Possible link of a structurally driven spin flip transition and the insulator-metal transition in the perovskite La${}_{1-x}$Ba${}_x$CoO${}_3$

Abstract

The complex nature of the magnetic ground state in La${}_{1-x}$A${}_x$CoO${}_3$ (A = Ca, Sr, Ba) has been investigated via neutron scattering. It was previously observed that ferromagnetic (FM) as well as antiferromagnetic (AFM) correlations can coexist prior to the insulator-metal transition (IMT). We focused on a unique region in the Ba phase diagram, from x = 0.17 - 0.22, in which a commensurate AFM phase appears first with a propagation vector, k = (0, -0.5, 0.5), and the Co moment in the (001)${}_R$ plane of the rhombohedral lattice. With increasing x, the AFM component weakens while an FM order appears with the FM Co moment directed along the (001)${}_R$ (=(111)${}_C$) axis. By x = 0.22, a spin flip to new FM component appears as the crystal fully transforms to an orthorhombic (Pnma) structure, with the Co moments pointing along a new direction, (001)${}_O$ (=(110)${}_C$). It is the emergence of the magnetic Pnma phase that leads to IMT.

5 pages