Neutron Scattering Study of Charge-Ordering in <i>R</i>_1/3Sr_2/3FeO₃(<i>R</i>=La, Pr, Nd, Sm, and Y)

Abstract

<p>The series of compounds <i>R</i>_1/3Sr_2/3FeO₃ (<i>R</i> = La, Pr, Nd, and Sm) undergo a Verwey transition along with an antiferromagnetic ordering of Fe spins as well as a slight structural distortion below the Verwey transition temperature, T_V. The charge disproportionation occurs via 3Fe^3.67+=>2Fe³⁺+Fe⁵⁺. The driving force of the charge ordering was determined from the magnetic and phonon spectra measured using inelastic neutron scattering. The data indicate a dominant role of the magnetic energy behind the charge ordering of Fe ions in La_1/3Sr_2/3FeO₃and Pr_1/3Sr_2/3FeO₃. Although Nd_1/3Sr_2/3FeO₃ has a larger antiferromagnetic exchange interaction, the charge ordering state can still be driven by the magnetic energy alone. The Fe-Fe Coulomb interaction in this system is discussed by changing <i>R</i>-site ions from La³⁺ to Nd³⁺. The effect of the electron-lattice interaction also plays a role to this ordering state.</p>