Enhancement of the Curie Temperature along the Perovskite Series RCu3Mn4O12 Driven by Chemical Pressure of R3+ Cations (R = Rare Earths)

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• 作者：Javier Snchez-Bentez ; Jos Antonio Alonso ; Mara Jess Martnez-Lope ; Alicia de Andrs ; Mara Teresa Fernndez-Daz
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：June 21, 2010
• 年：2010
• 卷：49
• 期：12
• 页码：5679-5685
• 全文大小：952K
• 年卷期：v.49,no.12(June 21, 2010)
• ISSN：1520-510X

文摘

The compounds of the title series have been prepared from citrate precursors under moderate pressure conditions (P = 2 GPa) and 1000 °C in the presence of KClO₄ as oxidizing agent. The crystal structures are cubic, space group Im (No. 204); the unit cell parameters linearly vary from a = 7.3272(4) Å (R = La) to a = 7.2409(1) Å (R = Lu) at room temperature. A neutron or synchrotron X-ray diffraction study of all the members of the series reveals an interesting correlation between some structural parameters and the magnetic properties. The electron injection effect upon replacement of Ca²⁺ with R³⁺ cations in the parent CaCu₃Mn₄O₁₂ oxide leads to a substantial increment of the ferrimagnetic Curie temperature (T_C). An essential ingredient is supplied by the internal pressure of the R³⁺ cations upon a decrease in size along the rare-earth series, from La to Lu: the concomitant compression of the MnO₆ octahedral units for the small rare earths provides progressively shorter Mn−O distances and improves the overlapping between Mn and O orbitals, thereby promoting superexchange and enhancing T_C by 50 K along the series. This interaction is also reinforced by a ferromagnetic component that depends on the local distortion of the MnO₆ octahedra, which also increases along the series, constituting an additional factor, via intersite virtual charge transfer t−e orbital hybridization, for the observed increment of T_C.