A-site substitution effects on the magnetic and lattice structure have been investigated for bilayer manganites, (La_1-zNdz)1.2(Sr_1-yCay)1.8Mn₂O₇, without changing the eg-electron concentration $(x=0.4)$. The ferromagnetic metallic (FM) phase of the parent La1.2Sr1.8Mn₂O₇ (TC=120 K) is suppressed by Nd doping $(z)$, and a paramagnetic insulating (PI) state appears above $z=0.3$. The FM phase is suppressed also by Ca doping $(y)$, but a layered-type antiferromagnetic (A-AF) structure appears above $y=0.3$. We have investigated the stability of the d_x²-y² (or d_3z²-r²) orbital by Madelung potential calculation based on the structural data, and have found that orbital polarization governs the magnetic structure in bilayer manganites.
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Akimoto et al. (1999) studied this question.
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