Magneto-electric cooling rate of a multiferroic antiferromagnetic quantum spin system: the cumulative influence of the site-dependent magnetic and electric fields
William Degaulle Waladi Gueagni, Lionel Tenemeza Kenfack, Martin Tchoffo, Georges Collince Fouokeng, Lukong Cornelius Fai
The magneto-electrocaloric effect which can be defined as the coupling between magnetocaloric and electrocaloric effects attracts currently considerable attention due to the advantages provided by the caloric effect in designing solid-state refrigeration technologies. The magneto-electrocaloric effect of a multiferroic antiferromagnetic spin system with the Dzyaloshinskii Moriya (DM) interaction is investigated in this paper. The DM interaction is assimilated to a coupling between an external site-dependent electric field and a local electric polarization. The external magnetic is also considered as a site-dependent magnetic field. The spin-wave theory is used as a diagonalization method and through the canonical partition function, some thermodynamic properties such as the Boltzmann entropy and the specific heat capacity are obtained. Then, the adiabatic magnetic, electric, and magnetoelectric cooling rates are also derived. The graphs obtained for the adiabatic magnetic, electric, and magnetoelectric cooling rate show a characteristic behavior of the caloric or multi-caloric effect which is in good agreement with some experimental and theoretical works. Besides, the entropy response due to the variation of the external site-dependent magnetic field exhibits two anomalous entropy peaks indicating the existence of an intermediate phase tuneable by the magnetic and electric site-dependent parameters. Overall, it is demonstrated that the cumulative influence of the site-dependent magnetic and electric fields allows us not only to reveal quantum critical points hidden in a multiferroic quantum spin system but also to control the caloric or multi-caloric effect essential in the construction of solid-state refrigeration devices.
University of Jinan（济南大学）；Institute for Superconducting and Electronic Materials, Faculty of Engineering and Information Sciences, University of Wollongong（伍伦贡大学工程与信息科学学院超导与电子材料研究所）
Magnetic-Field-Dependent Raman Scattering in Multiferroic Bilayer Films: Evidence for Stress-Mediated Magnetoelectric Coupling
首次报道了Pb（Zr，Ti）O_3-CoFe_2 O_4双层多铁体系的磁场相关拉曼散射研究。纳米双层膜的声子频率随着磁场的变化而发生明显的变化，而单层Pb（Zr，Ti）O3膜则没有这种变化。CoFe 2 O 4层的磁致伸缩产生机械传递到Pb（Zr，Ti）O3层的应力，导致模式变化。观察到的磁场诱导软化的软模式的Pb（Zr，Ti）O3层承担着一个惊人的相似的直接磁电输出的双层，提供证据的应力介导的磁电耦合机制的多铁性双层。
Electric susceptibility of antiferromagnetic multiferroics with cycloidal spin order at magnetoelectric effect associated with collinear component of spins
Epitaxial growth of multiferroic Pb(Zr0.57Ti0.43)O3-Pb(Fe2/3W1/3)O3 solid-solution thin films and their magnetoelectric effects
本文报道了用脉冲激光沉积法外延生长单相[Pb（Zr 0.57 Ti 0.43）O3]0.8[Pb（Fe 2/3 W 1/3）O3]0.2（PZT-PFW）固溶体薄膜。X射线衍射测试表明薄膜具有四方晶系结构。该薄膜在室温下表现出铁电性和弱铁磁响应。磁电效应进行了研究，非线性磁电系数进行了测量，发现是可比的多铁性六方锰氧化物，但至少两个数量级小于多晶PZT-PFW薄膜。
Prediction of new multiferroic and magnetoelectric material Fe3Se4
目前，具有磁电耦合的多铁性材料在新型存储器件领域有着广泛的应用。在室温下制备具有强耦合铁电和亚铁磁有序结构的多铁性材料具有挑战性。硒化铁（Fe_3Se_4）单晶在室温下表现出铁电有序和磁有序共存的II型多铁性。我们研究了铁电金属Fe_3Se_4的晶格不稳定性、电子结构、铁电、亚铁磁有序和输运性质。态密度显示出在费米能级附近Fe-3d和Se-4p态的相当大的杂化，证实了其金属行为。Fe阳离子的磁矩遵循II型亚铁磁和铁电有序，计算出的总磁矩为4.25每晶胞（Fe 6 Se 8）。Fe-Se的强共价键性质导致其铁电性质。此外，对称性分析表明，3d-t2 g轨道有序的Fe亚晶格的倾斜是由于Jahn-Teller（JT）畸变引起的。这项研究为利用多铁性材料发展自旋电子学相关技术提供了进一步的见解。
Magnetoelectric Phase Diagrams of Multiferroic GdMn2O5
研究了多铁性GdMn_2 O_5在外加磁场中的电磁性质，绘制了该材料的磁电相。由于强磁电耦合，介电常数对GdMn 2 O 5中的相界高度敏感，这允许构建场-温度相图。观察到几个相变是强烈的场依赖于相对于场的方向和强度。沿着晶体学a轴的磁场的相图很好地对应于由Gd磁矩的90度旋转引起的极化步骤。我们的结果支持两个铁电亚晶格，Mn-Mn和Gd-Mn与强R-Mn（4f-3d）相互作用的极化在RMn 2 O 5的模型。
Magnetoelectric training of multiferroic domains in Mn$_2$GeO$_4$
ETH Zurich（苏黎世联邦理工学院）；Loughborough University（拉夫堡大学）；Paul Scherrer Institut（保罗谢勒研究所）；High Energy Accelerator Research Organization (KEK)（高能加速器研究机构）；University of Tokyo（东京大学）；Norwegian University of Science and Technology (NTNU)（挪威科技大学）
Multiferroic Properties of Electrospun CFO-BCTSn Nanocomposites for Magnetoelectric and Magnetic Field Sensing Applications
Jozef Stefan Institute（约瑟夫·斯蒂芬研究所）；University of Picardie Jules Verne（皮卡第朱尔斯·凡尔纳大学）；Cadi-Ayyad University, Faculty of Sciences and Technology（卡迪·阿亚德大学科学与技术学院）；University Mohammed VI Polytechnic (UM6P)（穆罕默德六世理工大学）；Aix-Marseille University - CNRS（艾克斯-马赛大学-法国国家科学研究中心）；Institute of Physics AS CR（捷克科学院物理研究所）
Magnetoelectrical control of nonreciprocal microwave response in a multiferroic helimagnet
对外场物理性质的控制是当代技术的基本要求。可以通过场效应晶体管中的栅极电场来控制电导，场效应晶体管是集成电路的主要部件。由电场引起的光学现象如电致发光和电致变色对于显示器和其它技术是有用的。微波传播的控制对于未来的无线通信技术也是必不可少的。固体中的微波性质主要由磁激发控制，而磁激发不容易由电场控制。这个问题的解决方案之一是利用磁感应铁电体（多铁性）。在这里，我们表明，微波非互易性，这是相反传播的微波之间的差异，可以逆转的外电场在多铁性helimagnet Ba $_2$ Mg $_2$ Fe $_{12}$ O $_{22}$。这一结果为微波特性的电控制提供了新的途径。
Magnetoelectric effect in multiferroic metals via a direct spin-charge interaction
Key Lab of advanced optoelectronic quantum architecture and measurement (MOE), and School of Interdisciplinary Science, Beijing Institute of Technology（北京理工大学光电量子架构与测量教育部重点实验室，交叉科学研究院）
Four-coloured Spin-wave Excitations in Multiferroic Materials
光磁电效应是多铁性材料中自旋激发的固有属性，与光-物质相互作用仅由介电常数和磁导率表示的传统材料相比，其光学性质急剧改变。我们对多铁性Ca 2CoSi 2 O 7和Ba 2CoGe 2 O 7在THz光谱范围内进行的偏振吸收实验表明，这种磁电自旋激发显示出四色性，即它们对于光束的两个传播方向（向前或向后）和两个正交偏振的所有四种组合都具有不同的颜色。我们发现，正交色性可以产生奇特的光学性质，如单向透明和零反射的这些激发，这可以打开一个新的视野，在光子学。单向透明性也与静态磁电现象有关，因此，这些光学研究可以为系统合成具有大直流磁电效应的新材料提供指导。
