Crystal structures and magnetic order of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba): Possible orbital glass ferromagnetic state

TL;DR

This study reveals that La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} compounds exhibit orthorhombic structures with ferromagnetic order and suggest an orbital-glass state caused by strong Mn-Ru hybridization.

Contribution

It provides the first neutron diffraction evidence of ferromagnetism and orbital-glass behavior in these mixed Mn-Ru perovskites, highlighting the role of hybridization.

Findings

All samples are orthorhombic Pnma with regular octahedra.

Ferromagnetic order appears below 200-250 K.

No orbital ordering observed, indicating an orbital-glass state.

Abstract

The crystallographic and magnetic properties of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba) were investigated by means of neutron powder diffraction. All studied samples show the orthorhombic perovskite crystal structure, space group Pnma, with regular (Mn,Ru)O{6} octahedra and no chemical ordering of the Mn3+ and Ru4+ ions. Ferromagnetic spin structures were observed below Tc ~ 200-250 K, with an average ordered moment of ~ 1.8-2.0 Bohr magnetons per (Mn,Ru). The observation of long-range ferromagnetism and the absence of orbital ordering are rationalized in terms a strong Mn-Ru hybridization, which may freeze the orbital degree of freedom and broaden the eg valence band, leading to an orbital-glass state with carrier-mediated ferromagnetism.