【摘要】：磁電阻材料在磁感應(yīng)、磁記錄等領(lǐng)域都獲得了廣泛的應(yīng)用。由磁性金屬與非磁性基體材料組成的復(fù)合體系由于豐富的界面效應(yīng),具有特殊的磁性和電子輸運(yùn)特性。盡管磁性金屬/非磁性基體薄膜的室溫磁電阻效應(yīng)已有大量研究,但是對(duì)其電子輸運(yùn)特性尚沒(méi)有一個(gè)統(tǒng)一的認(rèn)識(shí),對(duì)于如何進(jìn)一步提高磁電阻的數(shù)值和磁電阻效應(yīng)的產(chǎn)生機(jī)制等有待進(jìn)一步探究。研究表明,添加Fe、Co、Ni等磁性金屬元素到碳基及硅基等非磁性基質(zhì)中形成的納米復(fù)合薄膜材料,不僅導(dǎo)電性質(zhì)可以隨添加量變化,而且表現(xiàn)出可以調(diào)控的大的磁電阻效應(yīng)。因此,掌握復(fù)合膜中金屬磁性元素對(duì)非磁性基薄膜材料結(jié)構(gòu)與載流子遷移率等特性的影響規(guī)律,理解其磁電阻效應(yīng)產(chǎn)生機(jī)理,有利于推動(dòng)高性能、低成本的碳材料及硅材料等在電子信息領(lǐng)域的廣泛應(yīng)用,具有重要的科學(xué)意義和實(shí)用價(jià)值。本論文工作通過(guò)在多種非磁基體(窄禁帶半導(dǎo)體SiN、寬禁帶氧化物半導(dǎo)體ZnO、非晶C、絕緣體MgO)中摻雜過(guò)渡族元素(主要是高自旋極化率的FeCo),研究成分和結(jié)構(gòu)對(duì)磁電性能的影響。論文采用濺射沉積技術(shù)制備了具有室溫鐵磁性的鐵磁/非磁顆粒膜或多層膜的納米復(fù)合材料。用X射線衍射、透射電鏡、X射線光電子能譜、原子力與磁力顯微鏡等觀察和分析其結(jié)構(gòu)和物相。利用物理性能綜合測(cè)試系統(tǒng)測(cè)量薄膜的磁性、電性和磁電輸運(yùn)性質(zhì)。主要研究?jī)?nèi)容與結(jié)論如下:首先,用反應(yīng)磁控濺射沉積制備了FeCo-Si-N復(fù)合薄膜,在室溫沉積的條件下成功獲得FeCo顆粒分布在Si-N基體中的納米顆粒膜;用電子顯微分析和磁力顯微分析清晰表征出其結(jié)構(gòu)特征和磁性特征;系統(tǒng)研究了FeCo-Si-N薄膜的磁電輸運(yùn)特性,在室溫獲得了大的正磁電阻,磁電阻在寬的磁場(chǎng)區(qū)間內(nèi)隨磁場(chǎng)呈線性變化。通過(guò)磁性測(cè)量和磁電阻隨成分的變化關(guān)系分析,間接判斷出顆粒內(nèi)的磁疇結(jié)構(gòu),得到了獲得最大磁電阻所需的結(jié)構(gòu)特征和規(guī)律;研究了溫度對(duì)薄膜磁電阻的影響,發(fā)現(xiàn)低溫下樣品的電子輸運(yùn)機(jī)制為隧穿導(dǎo)電,表現(xiàn)為隧道負(fù)磁電阻。在磁性FeCo納米顆粒截止溫度附近,正負(fù)磁電阻效應(yīng)發(fā)生轉(zhuǎn)變,表明該磁電阻與磁矩的排列有關(guān)。結(jié)果表明,薄膜大的室溫正磁電阻既有軌道效應(yīng)的影響,也有自旋效應(yīng)的影響。其次,制備了FeCo-ZnO納米顆粒薄膜并研究了磁電性能。發(fā)現(xiàn)濺射功率對(duì)FeCo-ZnO薄膜的影響很大。對(duì)于較低濺射功率制備的薄膜,FeCo不以零價(jià)的金屬態(tài)出現(xiàn),沒(méi)有FeCo團(tuán)簇,表現(xiàn)為正的磁電阻效應(yīng),并且磁電阻幾乎不受成分和厚度的影響,表明該正磁電阻與磁性的相關(guān)性小,極有可能來(lái)源于軌道效應(yīng)而不是自旋效應(yīng)。薄膜在220 K的磁電阻高達(dá)350%,這種正磁電阻值隨溫度急劇變化的表現(xiàn)說(shuō)明該磁電阻效應(yīng)與聲子的散射有關(guān)。而對(duì)于較高濺射功率下制備的薄膜,Fe、Co以零價(jià)的金屬態(tài)存在,薄膜具有超順磁性。在較厚的樣品中出現(xiàn)負(fù)磁電阻效應(yīng),可能來(lái)源于FeCo團(tuán)簇產(chǎn)生的隧穿磁電阻。此外,制備了FeCo與非晶碳復(fù)合的不同周期數(shù)的[C/FeCo]_n多層復(fù)合薄膜,研究了結(jié)構(gòu)和磁電性能。結(jié)果表明,隨著周期數(shù)增加,磁電阻MR由正值變?yōu)樨?fù)值。正磁電阻的大小與磁場(chǎng)成線性關(guān)系,而且在高場(chǎng)下也沒(méi)有飽和。通過(guò)薄膜電阻率隨溫度的變化行為研究了薄膜的傳導(dǎo)機(jī)制。對(duì)周期數(shù)不同的樣品的變程躍遷ln R--1/2與ln R--1/4曲線的擬合顯示,低溫下都屬于Efros變程躍遷,因此磁電阻為負(fù),但在高溫下,周期數(shù)少的薄膜由于熱激活不再是變程躍遷導(dǎo)電機(jī)制,磁電阻也轉(zhuǎn)變?yōu)檎?而周期數(shù)多的樣品由于界面和碳化物等缺陷的增加導(dǎo)致其局域化程度較強(qiáng),即使溫度升高也依然是變程躍遷,磁電阻保持為負(fù)值。研究表明,在2-300 K范圍內(nèi)傳導(dǎo)機(jī)制的轉(zhuǎn)變導(dǎo)致了磁電阻的轉(zhuǎn)變,證實(shí)傳導(dǎo)機(jī)制確實(shí)對(duì)磁電阻起著關(guān)鍵作用。最后,論文探索了FePt/C和FePt/MgO鐵磁-非磁復(fù)合膜的磁電輸運(yùn)性能及其在垂直磁記錄介質(zhì)方面的潛力。采用共濺射沉積的方法制備了FePt-C和MgO/[FePt-MgO]薄膜。利用C、MgO與FePt不互溶特性,在FePt顆粒間獲得C和MgO隔離物。研究了成分、退火溫度對(duì)FePt-C和FePt-MgO顆粒膜結(jié)構(gòu)和磁性能的影響。發(fā)現(xiàn)需要合適的隔離物含量以獲得較大的矯頑力。提高退火溫度有助于薄膜內(nèi)部FePt相的形成,從而獲得較大的矯頑力;但是,溫度過(guò)高會(huì)使薄膜的質(zhì)量遭到破壞,反而降低了矯頑力。此外,在FePt-C和FePt-MgO顆粒膜中還獲得了一定的磁電阻效應(yīng),分析了磁電阻的產(chǎn)生機(jī)制。綜上所述,本文采用磁控濺射沉積技術(shù)制備了鐵磁/非磁納米復(fù)合薄膜,在FeCo-Si-N、FeCo-ZnO和FeCo/C薄膜中獲得了較大的室溫磁電阻效應(yīng),并且通過(guò)結(jié)合其結(jié)構(gòu)、磁性、正負(fù)磁電阻的轉(zhuǎn)變和電阻的溫度變化關(guān)系等的分析,研究了薄膜的輸運(yùn)機(jī)制和磁電阻機(jī)制,對(duì)鐵磁-半導(dǎo)體復(fù)合膜中的自旋相關(guān)輸運(yùn)有進(jìn)一步的認(rèn)識(shí)。針對(duì)FePt-C和FePt-MgO顆粒膜,探索了其磁電阻效應(yīng),同時(shí)研究了成分、退火工藝等對(duì)其結(jié)構(gòu)和磁性能的影響,這些工作對(duì)自旋電子學(xué)的發(fā)展和自旋電子學(xué)器件的開(kāi)發(fā)以及新的磁記錄介質(zhì)材料開(kāi)發(fā)具有一定的借鑒意義。
[Abstract]:Magnetoresistance materials have been widely used in magnetic induction, magnetic recording and other fields. The composite systems composed of magnetic and nonmagnetic materials have special magnetic and electronic transport properties because of their rich interfacial effects. There is no unified understanding of the electronic transport characteristics. It is necessary to further explore how to further improve the value of magnetoresistance and the mechanism of the magnetoresistance effect. The study shows that the addition of magnetic metal elements such as Fe, Co, Ni and other non-magnetic substrates, such as carbon and silicon, is not only conductive. The effects of the magnetoresistance on the structure and carrier mobility of the nonmagnetic base film in the composite membrane, and the mechanism of the magnetoresistance effect are understood, and it is beneficial to push high performance, low cost carbon materials and silicon materials. Extensive applications in the field of electronic information have important scientific significance and practical value. This paper studies the doping of transition elements (mainly FeCo of high spin polarity) in a variety of nonmagnetic matrix (narrow band gap semiconductor SiN, wide band gap oxide semiconductor ZnO, amorphous C, insulator MgO), and studies the composition and structure of the magnetoelectric properties. The ferromagnetic / nonmagnetic particle film or multilayer nanocomposite with room temperature and ferromagnetism was prepared by sputtering deposition technique. The structure and phase of the film were observed and analyzed by X ray diffraction, transmission electron microscopy, X ray photoelectron spectroscopy, atomic force and magnetic force microscopy. The main contents and conclusions are as follows: first, FeCo-Si-N composite films were prepared by reactive magnetron sputtering. The nano particles of FeCo particles distributed in the Si-N matrix were successfully obtained under the condition of room temperature deposition. The structural characteristics and magnetic properties of the particles were clearly characterized by electron microanalysis and magnetic microanalysis. The magnetic and electrical transport characteristics of the FeCo-Si-N film are systematically studied. A large positive magnetoresistance is obtained at room temperature. The magnetoresistance varies linearly with the magnetic field in a wide range of magnetic fields. The magnetic domain structure in the particles is indirectly judged by the magnetic measurement and the relationship analysis of the magnetoresistance with the composition, and the necessary junction to obtain the maximum magnetic resistance is obtained. The influence of temperature on the magnetoresistance of thin film is studied. It is found that the electron transport mechanism of the sample at low temperature is tunneling conduction, which shows the tunnel negative magnetoresistance. The positive and negative magnetoresistance effect occurs near the cut-off temperature of the magnetic FeCo nanoparticles, indicating that the magnetoresistance is related to the arrangement of the magnetic moment. The temperature positive magnetoresistance has both the influence of the orbital effect and the influence of the spin effect. Secondly, the FeCo-ZnO nanocrystalline film is prepared and the magnetoelectric properties are studied. It is found that the sputtering power has a great influence on the FeCo-ZnO film. For the thin films prepared by the lower sputtering power, FeCo does not appear in the zero valence metal state and does not have a FeCo cluster, showing a positive magnetic field. The resistance effect, and the magnetoresistance is almost unaffected by the composition and the thickness, shows that the correlation between the positive magnetoresistance and the magnetism is small, and it may be derived from the orbital effect rather than the spin effect. The magnetoresistance at 220 K is as high as 350%, and the positive magnetoresistance values with the temperature change sharply indicate that the magnetoresistance effect and the scattering of the phonons are shown. The thin films of Fe and Co are superparamagnetic in the presence of zero valence metal states. The negative magnetoresistance effect in the thicker samples may come from the tunneling magnetoresistance produced by the FeCo clusters. In addition, the [C/FeCo]_n multilayer composite films with different periodic numbers of FeCo and amorphous carbon have been prepared. The results show that the magnetoresistance MR changes from positive to negative with the increase of the number of cycles. The size of the magnetoresistance has a linear relationship with the magnetic field and is not saturated at the high field. The conduction mechanism of the film is studied by the change of the resistivity with the temperature. The transition transition of LN R--1/ to the sample with different periodicity is changed. 2 and the fitting of the LN R--1/4 curve show that at low temperature, it belongs to the Efros transition transition, so the magnetoresistance is negative, but at high temperature, the thin film with less periodic number is no longer the transition conduction mechanism, and the magnetoresistance turns to positive value, and the number of periodic samples is localized due to the increase of the interface and carbide and so on. It is strong that the magnetoresistance remains a negative value even if the temperature rises. The study shows that the transformation of the conduction mechanism in the range of 2-300 K leads to the transition of the magnetoresistance. It is proved that the conduction mechanism does play a key role in the magnetoresistance. Finally, the magnetic and electrical transport properties of the FePt/C and FePt/MgO ferromagnetic nonmagnetic composite membranes are explored. The potential of the vertical magnetic recording medium. FePt-C and MgO/[FePt-MgO] films were prepared by CO sputtering. Using C, MgO and FePt insolubility, the separation of C and MgO between FePt particles was obtained. The effects of composition, annealing temperature on the structure and magnetic properties of FePt-C and FePt-MgO particles and magnetic properties were investigated. The increase of the annealing temperature can help the formation of the FePt phase inside the film and obtain a larger coercive force. However, the high temperature will destroy the quality of the film, but reduce the coercive force. In addition, a certain magnetoresistance effect has been obtained in the FePt-C and FePt-MgO granular films, and the production of the magnetoresistance is analyzed. In summary, the ferromagnetic / nonmagnetic nanocomposite films have been prepared by magnetron sputtering. The magnetoresistance effects in FeCo-Si-N, FeCo-ZnO and FeCo/C films have been obtained, and the film is studied by the analysis of the structure, magnetic properties, the change of the positive and negative magnetoresistance and the temperature change of the resistance. The transport mechanism and magnetoresistance mechanism have a further understanding of the spin dependent transport in the ferromagnetic semiconductor composite membrane. The magnetoresistance effect is explored for the FePt-C and FePt-MgO granular films, and the effects of the composition and annealing process on its structure and magnetic properties are also studied. The development of spintronics and the Spintronics are carried out. The development of parts and the development of new magnetic recording medium materials are of some reference significance.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TB383.2

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本文編號(hào)：2125624