同時具有鐵磁及鐵電有序的材料稱之為多鐵材料，而其中具有磁性電性交互作用的材料又特稱為磁電材料，此類型的材料在元件設計的應用上具有相當的淺力，依照磁與電的偶合方式來區分主有有兩大類，分別是稀土元素錳氧化物(RMn2O5)以及鉍鐵氧。本論文研究在此兩類型中各取一作為研究對象，鈥鑭錳氧及鉛鉍鐵氧。 本論文主要探討兩樣品的晶格結構以及磁性在摻雜之後所造成的變化。研究方法包含巨觀磁性量測、X光繞射、中子繞射和拉曼光譜等。 在鈥鑭錳氧樣品中，我們發現摻雜濃度達20%時，可以在140K以下開始觀察到新的磁性反應，拉曼散射譜圖在同一溫區也觀察到新的散射峰。此外，低溫長程磁有序的行為也因未摻雜而改變。鉛鉍鐵氧方面發現低溫磁結構也因為鉛的摻雜而改變了，根據中子繞射的數據顯示，磁結構為簡單反鐵磁。 The magnetic susceptibility, x-ray diffraction, neutron diffraction and Raman scattering measurements are employed to study the effects of La-substitution on the magnetic properties of multiferroic HoMn2O5. Both 9% and 18% La-doped compounds crystallize into the same orthorhombic Pbam symmetry as the parent compound. The magnetic responses to an ac driving magnetic field between 40 and 140 K are greatly enhanced by 18% La-doping. The neutron magnetic diffraction patterns reveal the development of short range magnetic correlations below 140 K. In addition, two Raman peaks and a series of new x-ray diffraction peaks suddenly develop below this temperature. Incommensurate long range antiferromagnetic order appears below 38 K. Magnetic frustration could be the main mechanism governing the present observations. Two Pb-doped BiFeO3 (5% and 10%) compounds were studied. The macroscopic magnetic measurement show the typical feature of the antiferromagnetic material. Weak ferromagnetic signals and the indication of spin reorientation at low temperatures were also observed in the two compounds. The magnetic structures for the two samples are basically simple antiferromagnetic arrangement but the magnetic moment direction is not yet determined. Further studies are still needed for complete understanding of the samples.
