鎳鋅銅亞鐵磁薄膜於鈦酸鍶、氧化鎂與玻璃基板上之成長、結構與磁性

Abstract

我們使用磁控濺鍍技術成長鎳鋅銅亞鐵磁薄膜於鈦酸鍶、氧化鎂與玻璃基板上。在此實驗中我們將研究成長條件對亞鐵磁薄膜的結構與磁性之影響以及結構和磁性之間的關係。 隨著成長溫度的上升，鎳鋅銅亞鐵磁薄膜的晶性會變好，但此現象僅有使用鈦酸鍶做為基板較為明顯。當我們將成長於鈦酸鍶基板上的薄膜厚度減小或是適度氧化後，它的飽和磁化量會明顯上升。因為鎳鋅銅亞鐵磁體的晶格常數較鈦酸鍶基板小，因此我們推測若鎳鋅銅亞鐵磁薄膜在成長過程中受到壓縮力，它的晶性和磁性都較好。 此外，我們發現在任何成長條件下，鎳鋅銅亞鐵磁薄膜的矯頑力(coercivity)和殘磁(remenance)皆較塊材大。當薄膜的成長溫度為650℃且厚度減小至10nm時，它的飽和磁化量是塊材的75%。

The structure of ferrite influences its magnetic and electric properties significantly, and the growth process is crucial to the structural behaviors of ferrites. Compared to bulk ferrites, there are more effects that could modify physical properties in ferrite thin films. In this work, we fabricate NiZnCu ferrite (NiZnCuFe2O4) thin films onto SrTiO3 (STO), MgO, and glass substrates by the magnetron RF sputtering technique in an ultrahigh vacuum system. The influences of growth conditions on magnetic properties and structures of NiZnCu ferrite thin films are studied. And the relations between the magnetism and the structure are also investigated. With the increase of substrate temperature, the spinel structure of NiZnCu ferrite films is formed and the magnetic moment is enhanced. But this effect is obvious only for films on STO. It reveals that compressive stress is conducive to the formation of spinel ferrites. The addition of oxygen could reduce oxygen vacancies in NiZnCu ferrite films under deposition. And we found a linear relation between the saturation magnetization and the inverse of the film thickness. According to the linear relation, we can predict that the NiZnCu thin film exceeds the bulk in the saturation magnetization as the thickness of the film is reduced to 6 nm. The coercivity and the remenance of films are greater than those of bulk ferrites under any growth conditions. The saturation magnetization of films with thickness of 10 nm and substrate temperature of 650 ℃ achieves 75 % of the bulk value.