Magnetic Properties and Microstructure of (FePt)_(1-x)Cr_x and (FePt)_(1-x)Cu_x Thin Films

(FePt)1-xCrx and (FePt)1-xCux thin films were deposited on quartz substrates by high-vacuum RF sputtering. X-ray diffraction patterns show that addition of Cr or Cu results in the suppression of the ordering transformation process while annealing temperature (T_a) was lower than 700℃. For T_a = 800℃, both the Cr- and Cu-containing alloys complete the disorder-to-order phase transformation within 20 minutes. After annealing at 800℃, very high coercivity of 12 kOe was obtained in FePt-Cr thin film. On the other hand, the alloying of Cu was found to increase magnetization. Microstructures of the thin films were studied from TEM micrographs. Large grain size and grain-boundary precipitants were observed in 800oC annealed FePt-Cr thin film. However, grain size refining was found in Cu-alloyed film. The ΔM curves were used to investigate the intergranular coupling. The ΔM values decrease with the increase of Cr concentrations. Whereas, the ΔM values increase with Cu concentration. It appears that the alloying of Cr decouples the grains while the addition of Cu results in strong exchange coupling.

關鍵字

FePt film ； fuse quartz substrates ； Cu-doping ； Cr-doping ； Magnetic properties ； Microstructure

並列摘要

本文以高真空磁控濺鍍系統製備(FePt)_(1-x)Cr_x 及(FePt)_(1-x)Cu_x 薄膜並研究其微結構及磁性。結構分析結果顯示Cr 或Cu 之添加於低於700℃之退火溫度（T_a）時抑制了序化相變化。當T_a = 800℃時，(FePt)_(1-x)Cr_x 及(FePt)_(1-x)Cu_x 兩系列薄膜皆於20 分鐘內完成序化相變化。經800℃退火後，FePt-Cr 薄膜可獲得高達12 kOe 之矯頑磁力。另一方面，Cu 之合金化被發現可提高磁化量。TEM 分析結果顯示FePt-Cr 薄膜經800℃退火後有較大之晶粒與晶界析出相產生；而FePt-Cu 薄膜則有細化晶粒之現象。ΔM-H 曲線顯示出ΔM 最大值隨Cr 含量提高而下降；但隨Cu 含量而提高。此揭示出Cr 合金化使晶粒間去耦合；而Cu 之添加可導致較強之晶粒間交換耦合效應。