鈷-碳非晶質薄膜之磁阻傳輸特性與電子結構探討

Magnetoresistance Property and Electronic Structure in Amorphous a-C:Co Films

莊霈于(Pei-Yu Chuang)

指導教授 ： 李志浩

國立清華大學/原子科學院/工程與系統科學系/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00305

摘要

非晶質碳膜(amorphous carbon, a-C)，近年在自旋電子學的研究上被預期極具潛力。本論文主要針對a-C:Co薄膜的磁電傳輸性質進行系統化研究，我們發現在a-C:Co薄膜系統中具有異常正磁阻。而此類正磁阻的效應，可能與近來研究報導所顯示之新型巨大磁阻的傳輸機制有關。這些系統的磁阻效應與早期的自旋電子散射機制不同，其磁阻變化率甚至更高。因此被預期有很大的應用潛力。
本實驗利用射頻磁控濺鍍系統，以共濺鍍方式製作a-C:Co薄膜，將鈷金屬摻雜在非晶質碳基底的薄膜內，將薄膜成長在石英基板上；在室溫的量測環境下，觀察到a-C:Co薄膜在外加磁場0.3 (T)的正磁阻變化率(~10%)，並隨著量測的外加偏壓變化，磁阻現象也有所對應。從I-V曲線關係圖觀察到a-C:Co薄膜擁有兩階段電阻，在電阻特性轉變處，其磁阻變化率為最大值。
為了解a-C:Co薄膜的正磁阻機制，我們藉由拉曼光譜(Raman)、X光反射率(XRR)、X光吸收光譜(XAS)、紫外光光電子能譜(UPS)、超導量子干涉儀(SQUID)，量測a-C:Co薄膜的密度、電子結構與磁化率，由實驗結果顯示，鈷與碳兩種元素的外層電子軌域互相混成形成複合材料。因此在外加磁場下，鈷金屬之d軌域受塞曼效應影響，d軌域發生分裂，可能導致a-C:Co薄膜的費米能階產生扭曲，進而影響電子傳輸，所以在磁阻的量測我們觀察到正磁阻現象。

關鍵字

正磁阻 ； 塞曼效應 ； 同步輻射

並列摘要

Recent studies of large magneto-resistance (MR) effect in several distinct mechanisms and systems have gained much attention because the MR ratio is comparable to, or even larger than, that of MR caused by a typical spin-dependent scattering mechanism discovered in magnetic multilayers. For examples, large positive MR induced by the space-charge effect has been achieved in metal-semiconductor hybrid devices. Besides, colossal MR related to switching the conducting channels between different layers has also been observed.
In this report, we study anomalous giant MR effect in amorphous a-C:Co films on the quartz substrate. These films, investigated in current-in-plane geometry, has a bias voltage dependent positive magneto-resistance (PMR), and at room temperature, the MR value reaches 10% under a relative low magnetic field H=0.3 (T) and bias voltage of 4V.
By using Raman spectrum、X-ray Reflectivity(XRR)、X-ray Absorption Spectrum(XAS)、Ultra-Violet Photoemission Spectrum(UPS) and Superconducting Quantum Interference Device(SQUID), we measure a-C:Co films the mass density、electron structure and magnetic properties to investigation of coupling the electro-transport. The result of Co and Carbon electron orbital to hybrid, and applied external magnetic field the Co d orbital will be split by Zeeman Effect. And then maybe distorted a-C:Co Fermi level to effect electro-transport.

並列關鍵字

Positive-Magnetoresistance ； Zeeman effect ； synchrotron radiation

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