FePd薄膜結構與磁性之研究

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Title:	FePd薄膜結構與磁性之研究
Other Titles:	Structure and magnetic properties of FePd thin films
Authors:	李明育 LEE, MING-YU
Contributors:	王昌仁 WANG, CHANG-REN 應用物理學系
Keywords:	濺鍍法;擴散法 FePd;sputtering
Date:	2019
Issue Date:	2019-12-16T07:03:32Z (UTC)
Abstract:	面心正方結構的L1o FePd薄膜具有高的磁晶異向性能和大的飽和磁化量及居里溫度還有良好的化學穩定性，故近年來被受許多學者關注並著重在以底層效應、摻雜、成份改變影響及化學沉積提高其磁性之研究。本實驗先以不同濺鍍法並且改變靶距製備30 nm Fe50Pd50薄膜於玻璃基板上，進行不同溫度退火(Ta = 500 - 750 oC)，FePd經由退火後皆呈現水平磁異向性。隨著溫度之升高，其結構漸從面心立方轉變為面心四方，因而提高其矯頑磁力，但當溫度提升至750 oC，FePd薄膜從L1o相轉變為fcc結構，導致其矯頑磁力大幅降低。實驗結果顯示當靶距越遠，矯頑磁力隨之提升，且靶距的提高有助於降低序化溫度。此外，脈衝濺鍍法鍍製FePd薄膜在靶距為5 cm時，矯頑磁力較高，可能與初始狀態下所受到壓縮應力較大有關。再者，亦研究了在氮氣下製備FePd薄膜經不同溫度後退火研究其結構與磁性。隨著退火溫度的增加，FePd矯頑磁力有明顯的大幅上升。其矯頑磁力最高值為3.9 kOe，出現在氮氣下以直流濺鍍FePd薄膜經700 oC之退火。由於氮氣鍍製當靶距為5 cm時較與氬氣鍍製矯頑磁力提升100 %。氮氣的鍍製並且調控靶距，降低序化溫度區間較為顯著，使磁性之提升可能與初鍍態壓縮應力較大有關。最後，以非磁性銅膜做為頂層，進行不同溫度下擴散，隨擴散火溫度之提升，可進一步的提升其矯頑磁力，由於銅經擴散後會包覆硬磁性FePd晶粒以致降低晶粒之間交互作用，須以較大的磁場下來翻轉其磁區，因而可大幅提高其矯頑磁力至4.5 kOe。 L10 FePd film with a tetragonal structure has high magnetic crystal anisotropy, large saturation magnetization, Curie temperature and good chemical stability. In recent years, many groups have focused on the enhancement of magnetic properties by underlayer, doping, composition and chemical deposition. In this work, structure and magnetic properties of FePd films prepared by various sputtering methods with various distances between target and substrate, post annealed at various temperatures are systematically studied. FePd films deposited at room temperature followed by a rapid therml annealing exhibits in-plane magnetic anisotropy. The phase transformation from face-centered cubic to face-centered tetragonal with increasing Ta in FePd films enhances its coercivity. Nevertheless, the L10 phase is gradually transformed into fcc phase at higher Ta = 750 oC, improves the coercivity. Besides, longer the distances between target and substrate is, the higher the coercive force is, and the change of the distances between target and substrate is helpful to reduce the oredering temperature. In addition, when the distances between target and substrate is 5 cm, FePd film prepared by pulse sputtering method exhiits higher coercivity, which may be related to the large compression stress of as-deposited film. Furthermore, significant enhancement of coercivity to 3.9 kOe is also found for FePd films at nitrogen atmosphere. Finally, Cu was used as the top layer for diffusion at different temperatures. With the increase of annealing temperature, the coercivity was further increased. Since copper would be coated with hard magnetic FePd grains after diffusion, the interaction between grains is reduced and the magnetic field to reverse the magnetization is increased. As a result, the coercivity is significantly increased to 4.5kOe.
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