本文選題：多鐵性材料 + 自旋重取向��； 參考：《上海大學(xué)》2016年博士論文

【摘要】：磁性材料、磁制冷材料以及多鐵性材料作為功能材料,分別在磁存儲(chǔ)、低溫磁制冷系統(tǒng)以及新一代的快速讀寫方面具有巨大的應(yīng)用前景,一直是凝聚態(tài)物理和材料科學(xué)領(lǐng)域探索和研究的熱點(diǎn)材料體系。RCrO3(R=rare earth)體系豐富的磁相變、RFeO3(R=rare earth)中的各向異性磁熵變和A4B2O9(A=Co、Mn,B=Nb、Ta)體系報(bào)道的磁電相互調(diào)控,使得RFeO3、RFeO3和A4B2O9等氧化物材料體系成為眾多研究者關(guān)注的焦點(diǎn)。本論文工作對(duì)CeCrO3多晶樣品的合成和磁化翻轉(zhuǎn)、TbFeO3單晶中的各向異性磁熱效應(yīng)以及A4B2O9體系單晶的制備和多鐵性與磁電耦合效應(yīng)進(jìn)行了研究。全文共分為六章,主要內(nèi)容如下:第一章為緒論,綜述了RCrO3體系磁性、RFeO3體系磁熱效應(yīng)以及A4B2O9體系的磁電效應(yīng)的研究進(jìn)展。并闡述了本論文的研究目的和意義,以及主要的研究?jī)?nèi)容。第二章,介紹了與本論文工作相關(guān)的主要實(shí)驗(yàn)原理和方法,包括樣品制備、結(jié)構(gòu)分析(包括中子衍射、晶體Laue衍射,以及X射線粉末衍射的變溫測(cè)試與分析)、鐵電性相關(guān)測(cè)試以及物性測(cè)量系統(tǒng)PPMS-9T的交/直流磁性測(cè)量方法等。第三章,研究了CeCrO3多晶的合成與復(fù)雜的磁相變。我們首次采用電弧法制備了純相的CeCrO3多晶樣品,通過(guò)對(duì)CeCrO3多晶樣品進(jìn)行系統(tǒng)的磁性測(cè)量,確認(rèn)了CeCrO3的Ce3+與Cr3+磁矩之間的反鐵磁相互作用,并系統(tǒng)地研究了該樣品溫度和磁場(chǎng)誘導(dǎo)的磁相變,在該樣品中觀測(cè)到對(duì)溫度和磁場(chǎng)非常敏感的自旋翻轉(zhuǎn)效應(yīng),該效應(yīng)在磁存儲(chǔ)和磁開關(guān)等方面有著潛在的應(yīng)用。第四章,研究了TbFeO3單晶樣品的制備與各向異性磁制冷效應(yīng)。采用光學(xué)浮區(qū)法成功制備了單相的TbFeO3單晶,對(duì)TbFeO3單晶的磁熱效應(yīng)進(jìn)行了系統(tǒng)的測(cè)試,發(fā)現(xiàn)TbFeO3單晶在ab面和c軸之間存在明顯的各向異性磁熵變,這種各向異性磁熵變和較大的制冷量,有望通過(guò)旋轉(zhuǎn)樣品來(lái)實(shí)現(xiàn)磁制冷,對(duì)于各向異性磁熵變的實(shí)際應(yīng)用具有重要意義。第五章,研究了A4B2O9體系中的Co4Nb2O9、Mn4Nb2O9和Co4Ta2O9等單晶樣品的制備與磁電效應(yīng)。該系列單晶樣品均采用光學(xué)浮區(qū)法制備,其中Mn4Nb2O9比較特殊,由于多晶原料很難通過(guò)固相反應(yīng)法合成,我們發(fā)明了一種基于光學(xué)浮區(qū)法的一步法直接生長(zhǎng)其單晶樣品的方法。對(duì)于Co4Nb2O9單晶,我們?cè)谄鋋軸方向觀測(cè)到了磁場(chǎng)調(diào)控的電極化和電場(chǎng)調(diào)控的磁化現(xiàn)象,并通過(guò)中子衍射實(shí)驗(yàn)和精修給出了其磁結(jié)構(gòu)。我們發(fā)現(xiàn)Co4Nb2O9單晶具有較大的磁電耦合系數(shù),并且是非線性磁電耦合效應(yīng),這種強(qiáng)的磁電耦合效應(yīng)在實(shí)際的器件設(shè)計(jì)中具有重要意義。對(duì)于Mn4Nb2O9單晶,我們發(fā)現(xiàn)其磁熱曲線與Co4Nb2O9不同,其反鐵磁相變發(fā)生在c軸方向,并且沒有觀察到自旋反轉(zhuǎn)相變。通過(guò)變溫XRD測(cè)試,我們發(fā)現(xiàn)Mn4Nb2O9在奈爾溫度附近出現(xiàn)結(jié)構(gòu)相變,該結(jié)構(gòu)相變溫度點(diǎn)與其奈爾溫度一致,因此我們認(rèn)為其反鐵磁相變是由該結(jié)構(gòu)相變導(dǎo)致的。Co4Ta2O9單晶與Co4Nb2O9單晶顯示出相似的磁電耦合性質(zhì)。盡管Co4Ta2O9的奈爾溫度略低于Co4Nb2O9,但更加容易發(fā)生自旋翻轉(zhuǎn),有利于在實(shí)際應(yīng)用中進(jìn)行操控。第六章,歸納總結(jié)了本論文的研究工作,并對(duì)CeCrO3、TbFeO3單晶和A4B2O9體系單晶的研究前景進(jìn)行了展望。
[Abstract]:Magnetic materials, magnetic refrigerating materials and multi iron materials as functional materials have great application prospects in magnetic storage, low temperature magnetic refrigeration system and the new generation of fast reading and writing. It has been a hot material system.RCrO3 (R=rare earth) system of condensed state physics and material science, which has rich magnetic phase transition, R The anisotropic magnetic entropy change in FeO3 (R=rare earth) and the mutual regulation of magnetic and electricity reported by A4B2O9 (A=Co, Mn, B=Nb, Ta) system have made the system of RFeO3, RFeO3 and A4B2O9 oxide materials become the focus of many researchers. This paper works on the synthesis and magnetization reversal of the samples of CeCrO3 polycrystalline, and the anisotropic magnetothermal effect in the single crystal The preparation of single crystal and the effect of magnetic and magnetic coupling on the A4B2O9 system are studied. The full text is divided into six chapters. The main contents are as follows: the first chapter is the introduction, summarizing the research progress of the magnetic properties of the RCrO3 system, the magnetothermal effect of the RFeO3 system and the magnetoelectric effect of the A4B2O9 system. The second chapter introduces the main experimental principles and methods related to the work of this paper, including sample preparation, structural analysis (including neutron diffraction, crystal Laue diffraction, and temperature variation test and analysis of X ray powder diffraction), ferroelectric correlation test and PPMS-9T alternating / direct magnetic measurement of physical measurement system, and so on. Third In this chapter, we studied the synthesis and complex magnetic phase transition of CeCrO3 polycrystals. We first prepared pure phase CeCrO3 polycrystalline samples by arc method. By systematic magnetic measurements of CeCrO3 polycrystalline samples, the antiferromagnetic interaction between the Ce3+ and Cr3+ magnetic moments of CeCrO3 was confirmed, and the temperature and magnetic field induced magnetism of the sample were systematically studied. The spin flip effect, which is very sensitive to temperature and magnetic field, is observed in the sample. This effect has potential applications in magnetic storage and magnetic switching. In the fourth chapter, the preparation of TbFeO3 single crystal samples and the effect of anisotropic magnetic refrigeration are studied. The single phase TbFeO3 single crystal is prepared by the optical floating area method, and the single crystal of TbFeO3 is prepared. The magnetocaloric effect is systematically tested. It is found that there is an obvious anisotropic magnetic entropy change between the AB surface and the c axis of the TbFeO3 single crystal. This anisotropic magnetic entropy change and the larger refrigeration capacity are expected to realize magnetic refrigeration by rotating samples. The fifth chapter is of great significance to the actual use of the anisotropic magnetic entropy change. The fifth chapter studies the A4B2O9 body. The preparation and magnetoelectric effects of single crystal samples, such as Co4Nb2O9, Mn4Nb2O9 and Co4Ta2O9 in the series, are prepared by optical floating zone method. The Mn4Nb2O9 is very special, because polycrystalline materials are difficult to be synthesized by the solid state reaction method. A single step method based on the optical floating region method has been invented to develop the single crystal sample directly. For the Co4Nb2O9 single crystal, we observed the magnetization of the magnetic field controlled by the magnetic field and the control of the electric field in the direction of the a axis. The magnetic structure was given by the neutron diffraction experiment and the refinement. We found that the Co4Nb2O9 single crystal has a large magnetoelectric coupling coefficient and a nonlinear magnetoelectric coupling effect. This strong magnetoelectric coupling effect is found. It is of great significance in practical device design. For Mn4Nb2O9 single crystal, we find that the magneto thermal curve is different from that of Co4Nb2O9. Its antiferromagnetic phase transition occurs in the direction of C axis, and the spin reversal phase transition is not observed. Through the temperature variable XRD test, we found that the structure phase transition of Mn4Nb2O9 at Nair temperature is near, and the phase transition temperature point of this structure is also found. Nair has the same temperature, so we think that the antiferromagnetic phase transition is a similar magnetoelectric coupling property between.Co4Ta2O9 single crystal and Co4Nb2O9 single crystal caused by the structure phase transition. Although the Nair temperature of Co4Ta2O9 is slightly lower than Co4Nb2O9, it is more easy to have spin flip, which is beneficial to manipulate in practical application. The sixth chapter is summed up. The research work in this paper and prospects for the research of CeCrO3, TbFeO3 single crystal and A4B2O9 single crystal are prospected.
【學(xué)位授予單位】：上海大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O441.6

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