Fe/Mn/Cu3Au(001)交換耦合系統之磁易軸翻轉研究

Abstract

在二維磁性系統中，磁異向性可能受到晶格結構、薄膜介面、合金比例等影響而造成磁異軸翻轉。 在Fe/Mn/Cu3Au(100)超薄膜系統中，我們發現了一個造成磁異軸翻轉的新機制。成長於室溫的Fe/Mn/Cu3Au(100)超薄膜系統，以中能電子繞射術(MEED)、低能電子繞射圖(LEED)、磁光柯爾效應(MOKE)及光發射電子顯微術(PEEM)來量測其成長機制、晶格結構、磁性行為及磁域影像。在220K下量測不同厚度錳/Cu3Au(100)單晶基板之上成長6個原子層厚的鐵，可發現在錳的厚度從0到15個原子層的情況下，鐵的晶格結構維持體心立方結構(bct)，垂直方向原子間距維持約1.55 angstrom。而鐵的磁異軸約在3個原子層厚的錳的情況下發生磁異軸翻轉的情形，在3層錳以下為平行膜面異向性，3層錳以上則為垂直膜面異向性。同時，由磁滯曲線的研究發現鐵的矯頑力(coercivity)提升。並且由磁域的研究中可發現，在磁異軸翻轉前後，錳呈現了與鐵反平行排列的磁域。這些證據可解釋此磁異軸翻轉的機制可能是來自鐵磁層與反鐵磁層的交換耦合。在一系列變動不同厚度的鐵錳以及溫度的量測中，亦提供更明顯的證據支持此論點。

In 2-dimensional magnetic ultrathin film systems, the magnetic anisotropy may be changed due to the variation of crystalline structure, interface, and alloy composition, in which the change of easy axis is so-called the spin reorientation transition (SRT). In ultrathin Fe/Mn/Cu3Au(001) bilayer system, a new mechanism of SRT has been discovered based on the complete thickness and temperature dependent studies. The growth, crystalline structure, magnetism, and magnetic domain of room temperature grown Fe/Mn/Cu3Au(001) are measured by medium energy electron diffraction (MEED), low energy electron diffraction (LEED), magneto-optical Kerr effect (MOKE), and photoemission electron microscope (PEEM). In the 6 ML Fe/Mn/Cu3Au(100) system, the crystalline structure of Fe remains bct structure and the interlayer distance is about 1.55 angstrom as Mn thickness increasing from 0 to 15 ML. The magnetic easy axis changes from in-plane to out-of-plane direction as Mn thickness is up to 3 ML at 220 K. Meanwhile, large enhancement in coercivity with the increasing of Mn thickness was observed. Also, Mn reveals ferromagnetic domains, which are anti-parallel coupled with the Fe domains, and switch from in-plane to perpendicular with Mn thickness. These evidences suggest that the SRT is due to the exchange coupling in Fe (FM) and Mn (AFM) interface.