【作者】 许丽丽；

【导师】 刘技文； 安玉凯；

【作者基本信息】 天津理工大学 ， 材料学， 2012， 硕士

【摘要】 随着信息技术的飞速发展，集铁电性与铁磁性于一体的单相多铁材料受到人们的广泛关注，其在多态存储元件、自旋电子器件、存储介质、换能器、传感器和多功能设备等方面有重要的潜在应用。本文利用射频磁控溅射的方法，在Si（111）和Si（100）基片上制备了不同浓度、不同退火气氛的Fe、Co、Mn掺杂LiNbO₃薄膜，研究了不同掺杂元素、掺杂浓度、溅射气氛的氧氩比和退火气氛对薄膜铁电性和铁磁性的影响。利用X射线能谱仪（EDS）、X射线衍射仪（XRD）、X射线光电子能谱仪（XPS）和X射线吸收精细结构（XAFS）技术对薄膜的组分含量、晶体结构、物相、元素价态和吸收原子的局域结构进行了分析，利用振动样品磁强计（VSM）和多功能物理测试系统（PPMS）对薄膜进行铁磁性能测量，TF2000铁电分析仪和阻抗分析仪对薄膜进行铁电性测量，获得研究结果如下：1. Fe掺杂LiNbO₃薄膜为R3C空间结构，薄膜中存在氧空位。Fe在薄膜中主要以Fe₂₊和Fe₃₊形式共存，没有形成Fe金属和氧化物团簇。在Si（111）基片上，薄膜中Fe含量从3at%到7at%时，饱和磁矩随着Fe含量的增加而增大，在7at%时最大，为196emu/cm³。Fe含量增加到8.5at%时，饱和磁矩降低，继续增加Fe含量到11.5at%时，饱和磁矩又有所增加。在Si（100）基片上，7at% Fe掺杂LiNbO₃薄膜分别经过氩气、空气和氧气退火后，在空气下退火得到的饱和磁化强度最大，约为31emu/cm³。7at% Fe掺杂LiNbO₃薄膜的剩余极化强度为3.8×10-5μC/cm²，矫顽电场为25Kv/cm，铁电居里温度为630K。薄膜的磁性来源于不同占位的Fe₃₊之间的超交换作用以及Fe₂₊-O^2--Fe₃₊的双交换作用。2. Mn掺杂LiNbO₃薄膜为R3C空间结构，薄膜中存在氧空位。Mn在薄膜中主要以Mn²⁺和Mn³⁺形式共存，并没有形成Mn金属或氧化物团簇。在Si（111）基片上沉积的Mn掺杂LiNbO₃薄膜，当Mn含量从1.5at%到2.5at%时，薄膜的饱和磁矩随Mn含量的增加而增大，在2.5at%时最大，为28emu/cm³。3.5at% Mn掺杂LiNbO₃薄膜经过氩气、空气和氧气退火后，在空气下退火得到饱和磁矩最大，为24emu/cm³。在Si（100）基片上，当Mn的掺杂浓度从1.5at%到3.5at%时，薄膜的饱和磁矩随Mn掺杂量的增加而增大，在3.5at%时最大，接近41emu/cm³。3.5at% Mn掺杂的薄膜经过氩气、空气和氧气退火后，在空气下退火得到最大饱和磁矩。8at% Mn掺杂LiNbO₃薄膜的剩余极化强度（Pr）为0.002μC/cm²，矫顽电场（Ec）为29Kv/cm，铁电居里温度为686K。薄膜的磁性来源于Mn的3d和邻近Nb的4d轨道间的耦合以及不同价态Mn间的双交换作用。3. Co掺杂LiNbO₃薄膜为R3C空间结构。薄膜中存在氧空位。Co在薄膜中主要是以Co2+和Co3+形式存在，并没有形成Co金属或氧化物团簇。在Si（111）基片上，当Co含量从5at%到7.5at%时，薄膜的饱和磁矩随Co含量的增加而增大，在7.5at%时最大，为51emu/cm³，继续增加到14at%时，薄膜的饱和磁矩降低。5at% Co掺杂的薄膜经过氩气、空气和氧气下退火后，在空气下退火的饱和磁矩最大，为45emu/cm³。7.5at% Co掺杂LiNbO₃薄膜的铁磁居里温度为630K。在Si（100）基片上，当Co含量从5at%增加到8.5at%时，薄膜的饱和磁矩随Co含量的增加而增大，在8.5at%时最大，为33emu/cm³，继续增加Co含量，饱和磁矩降低。5at% Co掺杂的薄膜经过氩气、空气和氧气下退火后，在空气下退火的饱和磁矩最大，为30emu/cm³。5at% Co掺杂LiNbO₃薄膜的剩余极化强度（Pr）为0.01μC/cm²，矫顽电场（Ec）为20Kv/cm，铁电转变温度为675K。薄膜的磁性是由氧空位与Co离子间耦合产生磁极子而形成宏观磁性。更多还原

【Abstract】 With the development of information technology, single-phase multiferroics exhibitingcoexistence of ferromagnetism and ferroelectricity become the subject of intensiveinvestigations due to their potential applications in data-storage media, spintronic devices,multiple-stage memories, sensors, etc. M（Fe, Co, Mn）-doped LiNbO₃thin films are depositedon Si（111） and Si（100） substrates by RF magnetron sputtering technique. The effects ofpreparation parameters, such as doping concentration and annealing atmosphere, on theferroelectric and ferromagnetic properties of samples have been studied. The composition ofM-doped LiNbO₃films is determined by the X-Ray energy dispersive spectroscopy （EDS）.The structural, magnetic and ferroelectric properties are characterized by X-ray diffraction（XRD）, X-ray photoelectron spectroscopy （XPS）, X-ray absorption near edge spectra（XANES）, Extended X-ray absorption fine structure （EXAFS）, vibrating samplemagnetometer （VSM）, physics property measurement system （PPMS）, TF Analyner 2000and impedance analyzer. In this paper, the results show that:1. Space structure of Fe-doped LiNbO₃films is R3C. There does not exist metallic Feclusters or Fe oxide secondary phases and the Fe ions exhibit +3 and +2 valence states insamples. There existed oxygen vacancies in samples. For Fe-doped LiNbO₃films depositedon Si（111） substrates, the saturation magnetization （Ms） increases with the addition of Fecontent to reach a maximum value which is 196emu/cm³at 7at% Fe-doped, then followed bya decrease. For the sample deposited on Si（100） substrates, 7at% Fe-doped LiNbO₃films areannealed in Ar, Air and O2atmosphere. The maximum magnetic moment is about 31emu/cm³in Air annealing atmosphere. The ferroelectric Curie temperature of Fe-doped LiNbO₃film is630K. The remnant polarization and the coercive field of Fe-doped LiNbO₃film are3.8×10-5μC/cm²and 25Kv/cm, respectively. The origin of room ferromagnetism is ascribed tothe super-exchange interactions of Fe³⁺in different occupational sites, mediated by theoxygen ions and the double-exchange interactions based on the Fe²⁺-O^2--Fe³⁺pairs.2. Space structure of Mn-doped LiNbO₃films is R3C. There no exist metallic Mnclusters or Mn oxide secondary phases and the Mn ions exhibit +3 and +2 valence states insamples. There existed oxygen vacancies in samples. For Mn-doped LiNbO₃films depositedon Si（111） substrates, the Ms increases with the addition of Mn content to reach a maximumvalue at 2.5at% Mn doped, then followed by a decrease. The maximum magnetic moment is28emu/cm³. 3.5at% Mn-doped LiNbO₃films are annealed in Ar, Air and O2atmosphere andthe maximum magnetic moment is about 24emu/cm³in Air annealing atmosphere. For the sample deposited on Si（100） substrates, the Ms increases with the addition of Mn content toreach a maximum value at 3.5at% Mn doped, then followed by a decrease. The maximummagnetic moment is 41emu/cm³in Air annealing atmosphere. The ferroelectric Curietemperature of Mn-doped LiNbO₃film is 686K. The remnant polarization and the coercivefield of Mn-doped LiNbO₃film are 0.002μC/cm²and 29Kv/cm, respectively. The observedroom temperature ferromagnetism of Mn-doped LiNbO₃films could be ascribed to the d–delectron interaction between the Mn dopant and its neighboring Nb atoms and thedouble-exchange mechanism of Mn with mixed valences.3. Space structure of Co-doped LiNbO₃films is R3C. There no exist metallic Co clustersand Co oxide secondary phases and the Co ions mainly exhibit +2 and +3 valence states insamples. There existed oxygen vacancies in samples. For Co-doped LiNbO₃films depositedon Si（111） substrates, the Ms increases with the addition of Co content to reach a maximumvalue at 7.5at% Mn doped, then followed by a decrease. The maximum magnetic moment is51emu/cm³. The ferromagnetic Curie temperature of 7.5at% Co-doped LiNbO₃film is 630K.5at% Co doped LiNbO₃films are annealed in Ar, Air and O2atmosphere and the maximummagnetic moment is about 45emu/cm³in Air annealing atmosphere. For the sample depositedon Si（100） substrates, the Ms increases with the addition of Co content to reach a maximumvalue at 8.5at% Mn doped, then followed by a decrease. The maximum magnetic moment is33emu/cm³. 5at% Co-doped LiNbO₃films are annealed in Ar, Air and O2atmosphere and themaximum magnetic moment is about 30emu/cm³in Air annealing atmosphere. Theferroelectric Curie temperature of Co-doped LiNbO₃film is 675K. The remnant polarizationand the coercive field of Co-doped LiNbO₃film are 0.01μC/cm²and 20Kv/cm, respectively.The observed room temperature ferromagnetism of Co-doped LiNbO₃films could beascribed to the bound magnetic polarons （BMP）mechanism based on defects.更多还原