Role of Magnetic Exchange Energy on Charge Ordering in R1/3Sr2/3FeO3 (R = La, Pr, and Nd)

Inelastic neutron scattering is applied to study the role of magnetism in stabilizing the charge-ordered state in R{sub 1/3}Sr{sub 2/3}FeO{sub 3} (RSFO) (R=La, Pr, and Nd). The ratio of the ferromagnetic exchange energy J{sub F} and antiferromagnetic exchange energy J{sub AF}, |J{sub F}/J{sub AF}|, is a key indicator of the stability of the charge-ordered and antiferromagnetic ordered state. This ratio is obtained from the spin-wave spectrum by inelastic neutron scattering and is sufficiently large to suggest that the magnetic exchange energy alone can stabilize the charge-ordered state in La{sub 1/3}Sr{sub 2/3}FeO{sub 3} and Pr{sub 1/3}Sr{sub 2/3}FeO{sub 3}. The exchange ratio decreases from La{sub 1/3}Sr{sub 2/3}FeO{sub 3} to Nd{sub 1/3}Sr{sub 2/3}FeO{sub 3}, which indicates a gradual destabilization of the magnetic exchange mechanism for charge ordering in correspondence with the observed reduction in the ordering temperature.