本文選題：Ni基超導(dǎo)體 + 反鐵磁�。� 參考：《浙江大學(xué)》2016年博士論文

【摘要】：自1986年銅氧化物高溫超導(dǎo)體發(fā)現(xiàn)以來(lái),尋找新型非常規(guī)超導(dǎo)體及針對(duì)其微觀機(jī)理的研究,一直是凝聚態(tài)物理學(xué)科重要的研究方向之一。無(wú)論是銅氧化物超導(dǎo)體,還是最近發(fā)現(xiàn)的鐵基超導(dǎo)體,以及早期發(fā)現(xiàn)的重費(fèi)米子超導(dǎo)體,其母體均為反鐵磁體。通過(guò)化學(xué)摻雜引入載流子、或通過(guò)外加壓力調(diào)控,抑制其反鐵磁長(zhǎng)程序,系統(tǒng)呈現(xiàn)強(qiáng)烈的量子磁漲落,從而出現(xiàn)超導(dǎo)電性,因此人們認(rèn)為非常規(guī)超導(dǎo)電性起源于這種量子磁漲落。在更多的3d金屬化合物中,尋找具有不同長(zhǎng)程磁有序的化合物,通過(guò)對(duì)物理參量(如載流子濃度,壓力等)的調(diào)控,尋找新型非常規(guī)超導(dǎo)體,已成為大家公認(rèn)的有效方法。在過(guò)去的三十年里,人們相繼在Cu(3d9), Fe(3d6), Co(3d7),Ni(3d8),Mn(3d5),Cr(3d4)等3d金屬化合物中發(fā)現(xiàn)了超導(dǎo)電性,但有關(guān)其微觀機(jī)理遠(yuǎn)未達(dá)到共識(shí)。本論文在過(guò)去研究工作的基礎(chǔ)上,針對(duì)T1基Fe, Co, Ni, Cu金屬硫族化合物的磁性,超導(dǎo)電性和磁熱效應(yīng)開展了系統(tǒng)研究,獲得了一系列研究成果。全文共分為五章,其主要內(nèi)容如下：第一章,我們概述了鐵基超導(dǎo)體研究現(xiàn)狀及其對(duì)尋找新型非常規(guī)超導(dǎo)體的啟示,同時(shí)對(duì)磁相變中的臨界行為、磁熱效應(yīng)等與本文相關(guān)的一些物理問(wèn)題進(jìn)行了總結(jié)和評(píng)述。第二章,在采用自助熔方法成功生長(zhǎng)出TlCo2-xNixSe2和TlCo2-xNixS2系列單晶的基礎(chǔ)上,我們通過(guò)對(duì)其晶體和磁結(jié)構(gòu)、磁性及輸運(yùn)性質(zhì)等進(jìn)行系統(tǒng)觀測(cè)。結(jié)果發(fā)現(xiàn),對(duì)于TlCo2-xNixSe2系統(tǒng),TlCo2Se2(x=0)樣品為沿c軸螺旋式(121。)無(wú)公度的反鐵磁體,而在x=0.2的樣品中,演變?yōu)橛泄鹊姆磋F磁結(jié)構(gòu)。隨著Ni替代濃度的進(jìn)一步增加,系統(tǒng)反鐵磁Neel溫度(TN)先上升后下降并在約x=1.7處達(dá)到零K；隨后系統(tǒng)呈現(xiàn)大塊超導(dǎo)電性,超導(dǎo)臨界溫度(TC)隨著Ni含量的上升而單調(diào)增加,在x=2時(shí)達(dá)到最大值(3.7 K)。從而獲得了TlCo2-xNixSe2體系從無(wú)公度的反鐵磁體到超導(dǎo)體的演變相圖。而對(duì)于TlCo2-xNixS2系統(tǒng),其磁性和超導(dǎo)電性的相圖較為復(fù)雜。首先TlCo2S2為巡游鐵磁體,微量的Ni替代導(dǎo)致系統(tǒng)呈現(xiàn)變磁性并具有一系列有趣的臨界行為(下一章內(nèi)容)；隨著Ni替代濃度的進(jìn)一步增加,系統(tǒng)從巡游鐵磁體,經(jīng)過(guò)變磁體、反鐵磁體,最后進(jìn)入超導(dǎo)態(tài)。這兩個(gè)系統(tǒng)的磁性和超導(dǎo)電性相圖,為理解Ni基超導(dǎo)電性提供了一個(gè)新的視角,我們將在論文中進(jìn)行詳細(xì)討論。第三章, 如前所述,TlCo2S2為巡游鐵磁體,微量的Ni替代導(dǎo)致系統(tǒng)呈現(xiàn)變磁性,我們對(duì)TICo2S2和TlCo1.9Ni0.1S2兩單晶樣品的等溫磁化曲線M(H)進(jìn)行詳細(xì)觀測(cè),發(fā)現(xiàn)前者的鐵磁相變臨近三重臨界點(diǎn),其臨界指數(shù)滿足的標(biāo)度率,與三重臨界平均場(chǎng)理論一致。微量Ni元素(x=0.1)的替代導(dǎo)致系統(tǒng)呈現(xiàn)變磁性、較小的磁場(chǎng)可以把系統(tǒng)調(diào)控為鐵磁體,進(jìn)一步證實(shí)了TlCo2S2巡游鐵磁性相變確實(shí)在三重臨界點(diǎn)附近。這些研究結(jié)果說(shuō)明TlCo2S2為少有的三重臨界點(diǎn)磁相變規(guī)律的研究提供了一個(gè)極佳的實(shí)驗(yàn)平臺(tái)。第四章,針對(duì)我們研究組首次在TlNi2Se2中觀測(cè)到3.7 K具有重費(fèi)米子行為的超導(dǎo)電性,我們通過(guò)Cu對(duì)Ni的部分替代,成功合成了一系列TlNi2-xCuxSe2(0≤x≤0.69)單晶樣品,并對(duì)其輸運(yùn)性質(zhì)和磁性質(zhì)開展了系統(tǒng)的研究。結(jié)果發(fā)現(xiàn),該體系中Cu對(duì)Ni的最大替代濃度x=0.69,這可能與Cu在該類化合物中所呈現(xiàn)的價(jià)態(tài)(+1)有關(guān)；隨著Cu替代濃度的增大,超導(dǎo)臨界溫度單調(diào)下降,當(dāng)x=0.69時(shí),系統(tǒng)不再呈現(xiàn)超導(dǎo)電性。所有樣品在正常態(tài)均呈現(xiàn)Pauli順磁。第五章,另外,我們還成功地合成了具有準(zhǔn)一維結(jié)構(gòu)的TlFe3Te3單晶,通過(guò)對(duì)其結(jié)構(gòu)、磁性質(zhì)和輸運(yùn)性質(zhì)的系統(tǒng)觀測(cè),發(fā)現(xiàn)該化合物在220 K發(fā)生了順磁-鐵磁一級(jí)相變,并呈現(xiàn)微小的熱滯和磁滯行為。我們進(jìn)一步的磁熱效應(yīng)研究發(fā)現(xiàn),對(duì)于磁場(chǎng)沿著c軸,在220 K附近,當(dāng)磁場(chǎng)變化AH=0-1 T和AH=0-2 T時(shí),由Maxwell關(guān)系獲得磁熵變化最大值高達(dá)5.9和7.0J/kgK,明顯高于相同溫度和磁場(chǎng)范圍的大多數(shù)其他磁熱材料,說(shuō)明TlFe3Te3具有性能優(yōu)異的磁制冷效應(yīng),我們的實(shí)驗(yàn)結(jié)果為探索新型磁制冷材料提供了一個(gè)新的方向。論文的最后對(duì)我的博士論文工作進(jìn)行了總結(jié)。
[Abstract]:Since the discovery of copper oxide superconductors in 1986, the search for new unconventional superconductors and their microscopic mechanisms has been one of the most important research directions in condensed matter physics. The matrix of both copper oxide superconductors, the recently discovered iron superconductors and the early discovery of heavy fermion superconductors Antiferromagnets. Through the introduction of chemical doping to the carrier, or by the control of the pressure, the antiferromagnetic long procedure is suppressed. The system presents a strong quantum magnetic fluctuation, which leads to superconductivity. Therefore, people think that the unconventional superconductivity originates from this quantum magnetic fluctuation. In more 3D metal compounds, it is found to have different long range magnetic properties. In the past thirty years, people have found superconductivity in Cu (3D9), Fe (3d6), Co (3D7), Ni (3d8), Mn (3d5), Cr (3d4), etc., but related to its microcosmic effect in the past thirty years. The mechanism is far from consensus. On the basis of the past research work, the magnetic, superconductivity and Magnetocaloric Effect of T1 based Fe, Co, Ni, Cu metal sulfur compounds have been systematically studied and a series of research achievements have been obtained. The full text is divided into five chapters, the main contents are as follows: Chapter 1, we summarize the research of iron based superconductors In the second chapter, on the basis of the successful growth of TlCo2-xNixSe2 and TlCo2-xNixS2 series of single crystals, we pass on its crystal and magnetic field. The structure, magnetic and transport properties are systematically observed. It is found that for the TlCo2-xNixSe2 system, the TlCo2Se2 (x=0) sample is an uncommensurate antiferromagnet along the c axis (121.), and in the sample of x=0.2, it becomes a common antiferromagnetic structure. With the further increase of the Ni substitution concentration, the system anti ferromagnetic Neel temperature (TN) rises first. Decrease and reach zero K at about x=1.7; then the system presents bulk superconductivity, the superconducting critical temperature (TC) increases monotonously with the increase of Ni content, and reaches the maximum value at x=2 (3.7 K). Thus, the evolution phase diagram of the TlCo2-xNixSe2 system from the antiferromagnet to the superconductor is obtained. For the TlCo2-xNixS2 system, its magnetism and superconductivity The phase diagram of electrical conductivity is more complex. First, TlCo2S2 is a cruising ferromagnet, and a trace of Ni substitution causes the system to be magnetic and has a series of interesting critical behaviors (the next chapter); with the further increase in the Ni substitution concentration, the system is from the cruising ferromagnet, through the magnets, antiferromagnets, and finally into the superconducting state. These two systems The phase diagram of magnetic and superconductivity provides a new perspective for understanding the Ni based superconductivity. We will discuss in detail in the paper. In the third chapter, as mentioned earlier, TlCo2S2 is a cruising ferromagnet, and the micro Ni substitution causes the system to be magnetic. The isothermal magnetization curve M (H) of TICo2S2 and TlCo1.9Ni0.1S2 two single crystal samples is detailed. It is found that the ferromagnetic phase transition of the former is near the three critical point, and the scaling rate of the critical exponent is consistent with the theory of the three critical mean field. The substitution of the trace Ni element (x=0.1) causes the system to be magnetic, and the smaller magnetic field can be controlled as a ferromagnet, and it is confirmed that the ferromagnetic phase transition of the TlCo2S2 cruise is indeed three. Near the critical point. These results show that TlCo2S2 provides an excellent experimental platform for the study of the magnetic phase transition of a rare three critical point. Fourth, for the first time, our research group observed the superconductivity of the heavy fermion behavior of 3.7 K in TlNi2Se2. We have successfully synthesized a series of Cu to Ni. TlNi2-xCuxSe2 (0 < < x < 0.69) single crystal sample and systematic study of its transport properties and magnetic properties. The results show that the maximum substituting concentration of Cu to Ni in this system is x=0.69, which may be related to the valence state (+1) of Cu in this kind of compound; with the increase of Cu substitution concentration, the superconducting critical temperature drops monotonously when x=0.69, The system no longer presents superconductivity. All samples are Pauli paramagnetic in normal state. In addition, we have also successfully synthesized TlFe3Te3 single crystal with quasi one-dimensional structure. By systematic observation of its structure, magnetic properties and transport properties, it is found that the compound has a paramagnetic and ferromagnetic phase transition at 220 K, and presents a small size. In our further magnetothermal effect, we find that for the magnetic field along the c axis and near 220 K, when the magnetic field changes AH=0-1 T and AH=0-2 T, the maximum value of the magnetic entropy change from the Maxwell relationship is up to 5.9 and 7.0J/kgK, which is obviously higher than most other magnetothermal materials at the same temperature and magnetic field range, indicating that TlFe3Te3 is of a property. Excellent magnetic refrigeration effect, our experimental results provide a new direction for exploring new magnetic refrigerating materials. Finally, the thesis summarizes my doctoral thesis work.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O469

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