超薄La(0.7)Sr(0.3)MnO(3) / La(0.5)Ca(0.5)MnO(3)雙層異質結構磁電特性研究

Abstract

鈣鈦礦錳氧化物被證實由於電荷、自旋、軌道及晶格自由度的強關聯性而存在著豐富的物理特性，其中，La(0.5)Ca(0.5)MnO(3)具有CE-type反鐵磁及電荷有序現象。另一方面，La(0.7)Sr(0.3)MnO(3)在居禮溫度Tc = 380 K以下具有鐵磁金屬態，說明在此強關聯系統，只要些微改變摻雜的物質，可能使磁電特性上有著非常不同的現象。在本文實驗中利用脈衝雷射沉積法，分別製作不同厚度的單層La(0.5)Ca(0.5)MnO(3)與La(0.7)Sr(0.3)MnO(3)薄膜及La(0.7)Sr(0.3)MnO(3)(x nm) / La(0.5)Ca(0.5)MnO(3)(30 nm) / SrLaAlO(4)(001) ( x = 1.5、3、4.5、6、7.5)的雙層結構，研究薄膜不同厚度及雙層異質結構的磁電特性及之間可能的交互作用。 應變形態的不同可能影響La(0.7)Sr(0.3)MnO(3)薄膜的磁力線分布及磁異向性，因此，初步利用磁力顯微鏡(MFM)觀察發現，單層La(0.7)Sr(0.3)MnO(3)薄膜在外加磁場下及成長在La(0.5)Ca(0.5)MnO(3)上的雙層異質結構的磁力線分布皆會有所改變。比較單層個別薄膜與數種厚度的雙層異質結構之磁電特性，發現皆有相變轉變及特性的改變，本文將對造成改變的可能原因進行討論。

Perovskite manganites have been demonstrated to exhibit rich emergent physics owing to the strong correlations among the charge, spin, orbital, and lattice degrees of freedoms. Among them, La(0.5)Ca(0.5)MnO(3) has been found to have the CE-type antiferromagnetic and charge ordering transition, simultaneously. On the other hand, the La(0.7)Sr(0.3)MnO(3) exhibits the ferromagnetic metallic phase below Tc 侧 380 K, indicating that merely slight changes in doping compositions may lead to drastic effects on the magneto-transport properties of these strongly-correlated systems. In this work, single-layered La(0.5)Ca(0.5)MnO(3) and La(0.7)Sr(0.3)MnO(3) thin films with different thicknesses, as well as bilayered structure of La(0.7)Sr(0.3)MnO(3)(x nm) / La(0.5)Ca(0.5)MnO(3)(30 nm) / SrLaAlO(4)(001) (with x = 1.5, 3, 4.5, 6, 7.5) films were synthesized by the pulsed-laser deposition to investigate the effects of film thickness and possible interactions between the two different materials on magneto-transport properties of respective structures. We found that the magnetic anisotropy may be significantly modified by the type of strain imposed on the films. For instance, the preliminary magnetic force microscopy (MFM) study has shown that the magnetic line of force on the La(0.7)Sr(0.3)MnO(3) monolayer can be dramatically modified by the applied external magnetic field as well as by the underlying layer in the bilayered heterostructures. Systematic comparisons between the magneto-transport properties of single-layered films and that of the bilayered structures with comparable thicknesses were made and the underlying mechanisms giving rise to the observed results will be discussed.