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 R1/3Sr2/3FeO3 (RSFO) (R=La, Pr, and Nd). The ratio of the ferromagnetic exchange energy JF and antiferromagnetic exchange energy JAF, |JF/JAF|, 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 La1/3Sr2/3FeO3 and Pr1/3Sr2/3FeO3. The exchange ratio decreases from La1/3Sr2/3FeO3 to Nd1/3Sr2/3FeO3, which indicates a gradual destabilization of the magnetic exchange mechanism for charge ordering in correspondence with the observed reduction in the ordering temperature.