穿隧磁電阻，磁電容，及介面上狀態密度的相互關係

Interrelation Between the Magnetocapacitance, Tunneling Magetoresistance, and Interfacial Density of States

陳貞如(Jen-Ru Chen)

指導教授 ： 林敏聰

國立臺灣大學/理學院/物理研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02070

摘要

磁性穿隧元件(Magnetic Tunnel Junction)是由兩層鐵磁性的金屬薄膜，中間夾一絕緣層所構成。這樣的結構，最廣為研究的性質就是穿隧磁電阻(Tunneling Magnetoresistance)的效應，我們更進一步以交流的電源量測磁性穿隧元件，研究磁電容(Magnetocapacitance)的性質，也就是說在上下鐵磁層呈現平行或反平行態的時候，所量到的電容值的差異。磁電容的效應已經被發現和穿隧磁電阻的傾向是相反的，我們可以觀察到這一點從實驗上的數據並以理論的模型來計算和估計。
在理論上，鐵磁層和絕緣層的介面上的累積電荷密度造成具磁性的化學位能的改變，這樣的邊界性質會造成一介面電容的表現。我們從Julliére提出的理論和實驗上的參數之中，推導出一個磁電容，穿隧磁電阻和介面上的狀態密度的相互關係，而且可以得到在數目上和實際相近的狀態密度。此外，我們也量測改變溫度和偏壓下的穿隧磁電阻和磁電容。在把數據經過理論上的計算後而知道，和偏壓相關的數據可以得到一個和文獻上相符的狀態密度的改變；但在溫度相關的數據下，因為我們的理論參數裡面並未加入有和溫度相關的參數，所以並不符合。但此矛盾應是可以繼續在更完備的理論架構中被解決。

關鍵字

穿隧磁電阻 ； 磁電容 ； 介面 ； 狀態密度

並列摘要

The magnetocapacitance (TMC) of typical magnetic tunnel junctions (MTJs) has been measured, and the TMC diagram has an inverse appearance comparing to the tunneling magnetoresistance (TMR). We described the theorectical model of the effective capacitances from the spin-dependent chemical potential change which due to the charge density gradient at the interfaces. In the observed result, the TMC is consistent well with the theoretical model that we can derive a relation between the TMC, TMR and the interfacial density of states (IDOS). According to Julliére model and the actual parameters, the IDOS of the ferromagnetic electrode was estimated approximately the value near the realistic one of bulk. Futher more, the bias dependence and temperature dependence measurements of the TMR and TMC were carried out and related to the theoretical model exploring the behaviors of IDOS. We found that the IDOS is declining slowly with the increasing bias and corresponds to the other researches about it. However, the temperature-dependent expressed no reasonable IDOS variation because of no temperature-dependent considerations being joined in theoretical deductions.

並列關鍵字

Tunneling magnetoresistance ； magnetic tunnel junction ； magnetocapacitance ； interfacial density of states

參考文獻

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