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Role of Magnetic Exchange Energy on Charge Ordering in RSFO (R=La, Pr, and Nd)

Inelastic neutron scattering is applied to study the role of magnetism in stabilizing the charge ordered state in \emph{R}$_{1/3}$Sr$_{2/3}$FeO$_{3}$ (\emph{R}SFO) (\emph{R} = La, Pr, and Nd). The ratio of the ferromagnetic exchange energy (J$_F$) and antiferromagnetic exchange energy (J$_{AF}$), |J$_F$ /J$_{AF}|, is a key indicator of the stability of the charge ordered and antiferromagnetic ordered state. This ratio is obtained from the spin wave spectrum by inelastic neutron scattering and is sufficiently large to suggest that the magnetic exchange energy alone can stabilize the charge ordered state in La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ and Pr$_{1/3}$Sr$_{2/3}$FeO$_{3}$. The exchange ratio decreases from La$_{1/3}$Sr$_{2/3}$FeO$_{3}$ to Nd1$_{1/3}$Sr$_{2/3}$FeO$_{3}$ which indicates a gradual destabilization of the magnetic exchange mechanism for charge ordering in correspondence with the observed reduction in the ordering temperature.