Structure, magnetism and transport of the perovskite manganites Ln0.5Ca0.5MnO3 (Ln=Ho, Er, Tm, Yb and Lu)

It was found that the manganese perovskite oxides Ln0.5Ca0.5MnO3 (Ln=Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn–O–Mn angles were calculated to be ∼148–150°, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism of Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln3+ and Ca2+, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu0.5Ca0.5MnO3 containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu3+ and Ca2+. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system.

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