龐磁阻錳氧化物傳輸性質的研究

Abstract

龐磁阻(Colossal magnetoresistance; CMR)錳氧化物的電阻率與霍爾係數已在不同溫度下被測量。藉由比較霍爾電阻率ρH與磁化強度M，我們可以推導得到霍爾係數RH和反常的霍爾係數Rs 。由霍爾係數RH可以知道樣品中傳輸載子為電洞，並求得電洞的載子濃度nh。藉由雙能帶模型可以解釋RH較小的原因，並說明了傳輸性質包含了電子與電洞的行為，而反常的霍爾係數Rs表示自旋無序的程度。由實驗結果觀察到，在鐵磁相中La0.7Ce0.3MnO3的自旋無序較La0.7MnO3系統與La0.7Sr0.3MnO3及La0.7Ca0.3MnO3來的大。而由反常霍爾係數Rs與電阻的關係，提供了另一種從傳輸量測上研究散射機制的方法。利用實驗得到的霍爾係數，並配合遠紅外線光譜的分析，則可得到每個樣品中載子的有效質量。為了了解這些材料的傳輸特性，我們也做了一系列的低溫電阻率 之量測，綜合這些結果，可以更加了解CMR錳氧化物的傳輸行為及其基礎科學相關問題的研究。

The Hall resistivity and magnetoresistance of CMR manganites have been measured at different temperatures. By comparing ρH with the magnetization M, we have extracted the Hall coefficient RH and the anomalous coefficient Rs. The carriers are determined to be mainly hole-type, and carrier concentrations in these samples can be estimated. The small Hall coefficient is explained by the two band model. The anomalous Hall coefficient measures the degree of the spin-disorder, which is larger in La0.7Ce0.3MnO3 than in La0.7MnO3, La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3. It provides another way to study the mechanism of the carrier with spin scattering from the relation between the anomalous coefficient and resistivity. The relative effective mass for these samples can be deduced by the transport properties together with the analysis of the far-infrared spectroscopy. The temperature dependence of the resistivity at low temperature is further analyzed to understand the electric transport mechanism of CMR manganites.