Sr3YCo4O10.5薄膜的横向热电效应及其与磁性的关联

The laser induced transverse thermoelectric voltage (LITTV) effect in c-axis inclined thin films originates from the Seebeck coefficient anisotropy between ab-plane and c-axis of thin films. The response mechanism of this effect and its correlation with the magnetic properties have attracted less attention. Sr3YCo4O10.5, with significant structural anisotropy, larger Seebeck coefficient and room-temperature ferromagnetism, will be studied here. Epitaxial Sr3YCo4O10.5 thin films with element doping will be grown on c-axis inclined single crystal substrates. Maintaining the same crystal structure, other elements doping in Sr/Y or Co sites will be employed to adjust the thermoelectric and magnetic properties of inclined thin films. The LITTV signals of these thin films will be measured, and the evolution of typical characters of these signals as a function of basic thermoelectric parameters will be depicted. The response mechanism of this kind of effect will be discussed, combining with the heat conduction model. Putting the thin films in different（temperatures） magnetic phases，crossing paramagnetism，ferromagneticism and antiferromagnetism phase regions,the LITTV signals of thin films will be measured separately at zero field and certain field. The influence of magnetic properties on the voltage signal and the thermoelectric anisotropy will be studied. The origins of room-temperature ferromagnetism and larger thermopower in Sr3YCo4O10.5 will be investigated by considering the charge,spin and orbital orders,as well as oxygen deficiences of Sr3YCo4O10.5.

c轴倾斜外延薄膜的激光感生横向热电电压(LITTV)效应源于薄膜材料ab面和c轴的热电势各向异性ΔS=Sab-Sc，这一效应的信号响应机制及其与材料磁性的关联还少有报道。项目选取具有明显结构各向异性、较大热电势和室温铁磁性的Sr3YCo4O10.5为基本材料体系，拟在c轴倾斜单晶衬底上生长外延Sr3YCo4O10.5及其部分离子替代薄膜。在不改变材料基本晶体结构情况下，通过Sr/Y位和Co位微量元素掺杂改变薄膜材料的热电、磁输运性质，测量薄膜LITTV信号峰值、上升沿和下降沿等随材料输运性质的变化趋势，结合热传导模型讨论信号的响应机制。将薄膜置于不同温度下，跨越顺磁、铁磁、反铁磁三相区测量薄膜LITTV信号，以及施加外场磁化后的信号，并计算材料的热电各向异性，研究磁性对电压信号及材料热电各向异性的影响，讨论与电荷、自旋、轨道有序，以及氧缺位和铁磁性关联的机制。

四方超结构Sr3ReCo4O10.5+δ（Re=Y, Er）具有复杂奇妙的有序特征、室温铁磁性和掺杂调制的热电磁效应等物理性质，项目开展了Sr4-xRexCo4O10.5+δ（Re=Y, Er）系列多晶的制备表征、相结构演变、有序化相变、热电性质，磁性及调制机制的研究，探索了氧的化学计量比与有序化相变的关联，绘出了SrYCoO体系Y含量~温度的完整相图；进行了Sr3YCo4O10.5+δ的Co位掺Cu、掺Ca系列多晶，Sr位掺Mg系列多晶的系统研究，讨论了掺杂离子对SrYCoO微结构、有序态、Co3+/4+的价态和自旋态的改变，对热电性质、磁性的影响；系统研究Sr4-xRexCo4O10.5+δ（Re=Y, Er）体系的室温铁磁性，磁化强度-温度，磁滞回线，获得了系列的Tc温度，讨论了磁性调控机制，另外所有系列多晶的热电势在Tc连续，表明热电势从铁磁态到顺磁态没有突变。还进行了PLD生长Sr3YCo4O10.5+δ薄膜以及掺Mg、掺Ca薄膜和电输运的系统实验研究，制备出顺磁立方相和在低温有磁滞四方相薄膜，在c轴倾斜的立方相SrYCoO薄膜实现激光感生电压效应，掺Ca增大薄膜的热电势各向异性，提高LITV峰值；掺Mg的四方相薄膜呈沿单晶衬底c轴倾斜0°,5°,10°的外延生长，半导体电输运行为，Mg掺杂减低电阻率，具有磁的各向异性，立方相SrYCoMgO薄膜的LITV信号随Mg掺杂的提高而下降。.在Sr4-xYxCo4O10.5+δ (x=0~1.2) 系列多晶，发生(x=0)六方2H型(R32) SrCoO3-δ→(x=0.4)立方钙钛矿(Pm3 ̄m) Sr3.6Y0.4Co4O10.5+δ→(x=0.8,1.0)有序四方(I4/mmm)Sr3YCo4O10.5+δ的转变，各相随温度的相变。Y=0~1.2的SrYCoO总体为半导体热电输运行为，x=0的SrCoO3-δ电阻率最大；x=0.4时，Y3+的掺杂维持高对称性的钙钛矿结构，具有最小的电阻率和热电势；x=0.4~1.0，晶粒细化，Co4+部分转变为Co3+，载流子浓度下降，电阻率和热电势提高。x=1.0四方超结构Sr3YCo4O10.5+δ具有室温铁磁性，Tc~335K，T=333K明显Hopkinson峰，ZF曲线263K有最大M，210K发生铁磁-反铁磁转变，生成G-type反铁磁相。