a軸取向正交結構鎦錳氧薄膜之磁性與電性研究

Abstract

本研究使用脈衝雷射濺鍍系統在摻鈮鈦酸鍶(110)基板上成功製備出a軸垂直基板且軸向分離之正交結構鎦錳氧薄膜，並研究其磁性與電性。我們使用超導量子干涉儀量測磁化率與溫度變化關係，發現兩個磁性轉折點：第一個轉折點在a、b、c軸都有觀測到為尼爾溫度，約在43K，是由錳的反鐵磁磁序引起的；第二個轉折點只有發生在b軸約在30K，可能為錳的磁矩重新排列所導致的。電性測量發現a軸方向上相對電容率在30K附近有轉折，但是由極化對電場的曲線卻沒觀察到自發性極化，與理論預測之磁電關連性不同，推測可能是應變造成的影響。

We have investigated the structure and magnetic properties of the a-axis-oriented orthorhombic LuMnO3 (o-LuMnO3) films deposited on Nb-doped SrTiO3 (110) substrate by pulsed laser deposition. We observed the anisotropic properties in magnetic structure of o-LuMnO3 by using SQUID (Superconductor Quantum Interference Device) to measure the temperature dependent susceptibility. Two distinctive magnetic transitions were observed for o-LuMnO3 films. The first one locating around 43K was observed universally in each axis and presumably associated with the antiferromagnetic ordering of Mn moment. Consequently, it is assigned as the Neel temperature (TN). The second transition was observed around 30K only when the field was probed along the b-axis, which could be caused by Mn spin reordering. By electric measurement, a transition of the relative permittivity around 30K in a-axis was observed, but the spontaneous polarization was not seen in the electric field dependent polarization curves. It is different from the magnetoelectric correlation predicted by recent theories for these E-type multiferroic manganites. We suspect that the strain effect inherently existing in these epitaxial strain-stabilized orthorhombic films might have played a role.