以第一原理研究1-3曾鐵覆蓋在鈣鈦礦結構(ABO3, A=Ba、Pb、Sr, B=Ti, Zr)的磁電效應

The First Principle Study on Magnetoelectric Coupling in Fex/ABO3 (x=1-3, A=Ba、Pb、Sr, B=Ti、Zr)

黃偉鳴(WEI-MING HUANG)

指導教授 ： 梁贊全

國立中正大學/理學院/物理學系/碩士(2016年)

摘要

多鐵材料可透過外加作用改變本身的自發性有序性質，使得在現今的材料應用與研究上
有更多元的發展，有許多研究發現可利用多鐵材料中的鐵電性調控鐵磁性或是利用鐵磁性調
控鐵電性。對高密度磁性儲存元件來說，奈米尺度磁性材料的垂直異向性是一個重要的物理
特性，其中磁晶異向能是描述垂直異向性的重要指標。文獻上已有許多的團隊針對多鐵複合
薄膜Fe/BaTiO3 進行磁晶異向能的計算研究，研究結果證實計算多鐵薄膜在不同電極化方向
的磁晶異向能大小是不一樣的。
本論文以第一原理研究六種鈣鈦礦結構的鐵電塊材(ABO3,A=Ba、Pb、Sr, B=Ti、
Zr)，其結構性質以及鐵電性質隨不同拉壓的變化。也以此六種鐵電材料為基板其上覆蓋1-3
層鐵構成Fex/(ABO3)3(x=1,2,3) 的多鐵薄膜系統，計算其P" 與P# 的磁晶異向能來探討磁
電效應。
研究結果顯示塊材計算的部分，PbZrO3 具有較強的自發電極化強度，而BaZrO3 的鐵
電性非常微弱。而自發電極化強度隨拉壓效應變大而減少。多鐵薄膜系統計算的部分，研究
結果顯示，磁晶異向能在不同電極化方向(Pup 與Pdn) 的改變量最大的是以PbZrO3 為鐵電基
板的多鐵薄膜系統隨著覆蓋鐵層增加其改變量為1.09、0.53、0.56meV。我們認為以電極化
強度高的材料作為基板，可以有效透過電極化方向不同而改變磁晶異向能。另外，我們也計
算在外加電場0.2 V/Å 下的磁晶異向能，我們發現外加電場對磁晶異向能造成的影響並不明
顯，其中只有SrTiO3-Pup 的系統有較明顯的不同，隨鐵層增加其磁晶異向能依序為0、0.18、
0.86meV。我們也利用微擾理論分析各系統的磁晶異向能在k 空間第一布里淵區的分布，我
們發現所有系統的分布情形類似，其中一階微擾的總貢獻為0，而二階微擾的貢獻會隨著鐵
層數的增加最後，而主要負貢獻會集中於k 空間中心區域而主要正貢獻會傾向集中於中心外
圍的區域。

關鍵字

磁晶異向能 ； 垂直異向性 ； 自發電極化 ； 磁電耦合 ； 多鐵材料 ； 鐵電 ； 鐵磁

並列摘要

Multiferro materials , which have two or more ferro-properies simultaneously, can
change the self-spontaneous order-parameter by external electric field or external magnetic
field. Multiferro materials have a lot of attractive properties on material applications and
material researches. Many researches found that they can control the magnetism by external
electric field or control the electricity by external magnetic field though the Multiferro materials.
This characteristic is called magnetoelectric effect. For high density magnetic storage
device, the vertical anisotropy in nanomagnetic materials is a important physical properties,
one of the most important properties is magnetocrystalline anisotropy energy(MAE). Many
reserchers investigate the magnetocrystalline anisotropy energy on Fe/BaTiO3 multiferro
heterostructure and they calculate the MAEs, which orientation of polarization is different,
is not the same.
In this thesis, we have two parts to analysis . in the first part, we used the first principle
calculation to study six ferroelectric materials by perovskite structure (ABO3, A=Ba, Pb,
Sr, B=Ti,Zr ). We study structure properties and ferroelectric properties under the strain
effect. in the second part , we also used the first principle calculation to study magnetoelectric
coupling in Fex/ABO3 (x=1,2,3) multilayer. We calculate the MAE for Pup and Pdn
types and also investigate the MAE distribution in K-space for each case.
According to our results. In the first part, we found that the spontaneous polarization
for the largest one and the lowest one is PbZrO3 and BaZrO3 respectively in our 6 materials.
The spontaneous polarization will decrease when the strain effect increase. In the second
part, we found that the largest MAE change between the different polarization direction is
Fe/PbTiO3 system. We conclude that we use the substrate with high ferroelectric properties
and we can change the MAE for different polarization direction effectively. Also we
calculate the MAE under the external electric field and we found that the MAE changes
are not obvious. There is only one system that Fe/SrTiO3 have a little change under the
external electric field.

並列關鍵字

spontaneous polarization ； magnetic anisoproty energy ； vertical anisotropy ； ferromagnetic ； ferroelectric ； multiferro material ； magnetoelectric coupling

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