Crystal structures and magnetic order ofLa0.5+δA0.5−δMn0.5+ϵRu0.5−ϵO3(A=Ca,Sr,Ba): Possible orbital glass ferromagnetic state

The crystallographic and magnetic properties of La 0.5+δ A 0.5-δ Mn 0.5+e Ru 0.5-e 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 Mn 3+ and Ru 4+ ions. Ferromagnetic spin structures were observed below T c ~ 200-250 K, with an average ordered moment of ~ 1.8-2.0µ B (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 e g valence band, leading to an orbital-glass state with carrier-mediated ferromagnetism.