摻雜錳原子對Cd1-xMnxSe奈米顆粒磁性之影響

Abstract

過去二十年來，半導體奈米顆粒由於其所具有的新穎物理性質以及其作為製造奈米元件最小單位的潛力而廣受科學家關注。為了進一步控制奈米顆粒的物理性質，科學家試著摻雜各種不同元素以控制半導體奈米顆粒的物理特性。摻雜磁性原子的半導體奈米顆粒，即稀磁半導體奈米顆粒，由於其結合了磁學，光學，與電學的性質在近幾年來引起科學家的注意。然而，至今仍然少有文獻討論摻雜磁性原子對稀磁半導體奈米顆粒的磁學性質之影響。 在本論文中，我們將討論摻雜錳原子之硒化鎘奈米顆粒磁性之影響。我們使用超導量子干涉磁量儀量測摻雜錳原子之硒化鎘奈米顆粒在低溫下磁化量隨磁場變化之行為，以及其在小磁場下磁化量隨溫度變化之行為。我們觀測到在低溫以及大磁場下將有一磁化量不飽和的現象，此現象隨著錳原子摻雜濃度越高而越明顯，並且不能被錳原子內部自由載子產生的庖利順磁所解釋。我們在小外加磁場下量測磁化率對溫度的變化，由量測與最佳擬合的結果可知其小磁場下磁化率對溫度的變化行為不能被居理定律所解釋。在考慮奈米顆粒中自由載子本身的庖利順磁後我們發現在摻雜濃度越小的情況下摻雜錳的硒化鎘奈米顆粒其磁性較接近磁性原子的磁性與庖利順磁的疊加，當摻雜濃度越高由於摻雜錳原子對庖利順磁的磁性影響越顯著因此其磁性行為越不能被磁性原子的磁性與奈米顆粒本身磁性的疊加所解釋。

Semiconductor nanocrystal has been widely studied in last two decades, not only because the novel physical properties it has but also the potential of been building block of nanodevice. To modify semiconductor nanocrystal’s physical properties, doping impurities in nanocrystal is a widely used approach. Magnetic ion doped semiconductor nanocrystal, named diluted magnetic semiconductor nanocyrstal (DMSNC), such like Cd1-xMnxSe, Cd1-xMnxTe etc., has attracted scientists attention in recent years because of its potential of been new building block of nanodevice and combination of magnetic , electrical, and optical properties. Although the optical properties in this kind of material have been widely studied and the magnetic properties have been discussed in theoretical approach, the experimental study of magnetic properties in DMSNC is still lack. In this article, the magnetic properties of Cd1-xMnxSe nanocrystal with different size (d=5, 8 nm) and concentration (x=0.375 %, 0.15 %) have been studied by using SQUID magnetometer. Magnetic field dependence of magnetization (M-H curves) has been measured under 2 K and temperature dependence of magnetic susceptibility (χ-T curves) has been measured under external magnetic field in 100 Oe. The non-saturated phenomenon has been observed in all of the M-H curves. This phenomenon has been more manifest in higher concentration sample. We also observed that Curie law can not explain the χ-T curves of all of our samples because the nonzero magnetic susceptibility under high temperature region. After considering the Pauli paramagnetism comes from the free carriers in nanocrystals, we observed that, in lower concentration samples, magnetic properties could be explained by a summation of magnetic properties come from the Mn ions and the free-carriers in nanocrystal. However, in higher concentration samples, the Mn ions will affect the magnetic properties of free-carriers in nanocrystal thus making the magnetic properties more complex.