单相ABO3型多铁材料的磁电耦合及磁电性质研究

实验发现多铁性钙钛矿物质YMnO3和BiMnO3在接近磁有序相变温度时,其介电常数和正切损失会出现异常,这些现象说明在物质的磁性和介电性质之间存在耦合.通过对系统磁性和铁电性之间可能磁电耦合方式的分析,考虑在系统哈密顿量中加入与自旋关联和极化相关的耦合项,对铁电子系统应用软模理论,对磁性运用基于海森伯模型的量子平均场近似,研究了外磁场诱导的极化、介电的变化和外电场诱导的磁化的变化等,并将以上结果与实验进行了比较和分析,较为合理地解释了一些多铁钙钛矿物质中的磁电现象.     

铁电磁体Pb(Fe1/2Nb1/2)O3的磁电性能研究

对铁电磁体Pb(Fe_1/2Nb_1/2)O₃单晶样品中的 介电和磁性能进行了研究. 认为在其反铁磁相变点观察到的介电常数和损耗的异常来自于自发极化序和自旋序的相互作用 引起的磁电耦合. 磁矩与温度的关系曲线在Nel点以下的低温段呈上升趋势，测得的磁滞 回线证明有弱铁磁性出现. 对铁电磁体磁电相互作用的Monte Carlo模拟得到与实验类似的 结果. 关键词： 铁电磁体 1/2Nb_1/2)O₃')" href="#">Pb(Fe_1/2Nb_1/2)O₃ 磁电耦合 Monte Carlo模拟     

顺磁性La2/3Sr1/3MnO3层对Bi0.8Ba0.2FeO3薄膜多铁性能的影响

界面效应在提升异质结构材料的多铁性能方面有着重要的作用. 本文采用脉冲激光沉积技术在SrTiO₃(STO)基片上制备了Bi_0.8Ba_0.2FeO₃(BBFO)/La_2/3Sr_1/3MnO₃(LSMO)异质结. X-射线衍射图谱表明异质结呈现单相外延生长, 利用高分辨透射电镜进一步证实了BBFO为四方相结构. X-射线光电子能谱证实异质结中只存在Fe³⁺ 离子, 没有产生价态的变化, 揭示了异质结铁电和铁磁性的增强与BBFO/LSMO的界面有关. 同时, 测试了磁电阻(MR)和磁介电(MD), 当磁场强度为0.8 T, 温度为70 K时, MR约为-42.2%, MD约为21.2%. 并且发现在180 K时出现磁相的转变. 实验结果揭示出异质界面效应在提升材料的多铁性和磁电耦合效应方面具有超常的优点, 是加快多铁材料实际应用的有效途径.     

铁电磁体Pb(Fe1/2Nb1/2)O3的磁电性能研究

对铁电磁体Pb(Fe1/2Nb1/2)O3单晶样品中的介电和磁性能进行了研究. 认为在其反铁磁相变点观察到的介电常数和损耗的异常来自于自发极化序和自旋序的相互作用引起的磁电耦合. 磁矩与温度的关系曲线在Néel点以下的低温段呈上升趋势,测得的磁滞回线证明有弱铁磁性出现. 对铁电磁体磁电相互作用的Monte Carlo模拟得到与实验类似的结果.     

A位的Gd掺杂对La0.7Sr0.3MnO3体系磁电性质的影响

通过实验研究了La_0.7-xGd_xSr_0.3MnO₃(x= 0.00，0.10，0.15，0.20，0.30 ，0.40，0.50，0.60，0.70)体系的M-T曲线、M-H曲线、红外光谱、拉曼光谱、ρ-T曲线和M R-T曲线.实验结果表明：随着Gd掺杂的增加，体系从长程铁磁有序向自旋团簇玻璃态和反铁 磁状态转变，高掺杂时的输运性质在其磁背景下发生异常.Gd掺杂引起的磁结构变化和额外 的磁性耦合将导致庞磁电阻效应. 关键词： 磁结构 输运行为 庞磁电阻效应     

La2/3Sr1/3MnO3/BaTiO3复合薄膜的制备及其电致磁电效应研究

使用脉冲激光沉积技术,在LaAlO₃(001)单晶基片上制备了La_2/3Sr_1/3MnO₃(LSMO)/BaTiO₃(BTO)双层薄膜.X射线衍射分析显示,LSMO层和BTO层呈现纯(001)取向.原子力显微镜研究表明,薄膜表面晶粒大小均匀,排列致密,表面均方根粗糙度为1.4 nm.复合薄膜的磁学、电学性能研究表明,其具有良好的磁学和介电性能.电输运测试显示,与在BTO层上施加正方向 关键词： 磁电效应 铁电/铁磁异质结构 脉冲激光沉积     

多铁异质结构中逆磁电耦合效应的研究进展

电场调控磁性能够有效降低功耗,在未来低功耗多功能器件等方面具有巨大的潜在应用前景.铁磁/铁电多铁异质结构是实现电场调控磁性的有效途径,其中室温、磁电耦合效应大的应变媒介磁电耦合是最为活跃的研究领域之一.本文简要介绍在以Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_3为铁电材料的多铁异质结构中通过应变媒介磁电耦合效应对磁性、磁化翻转及磁性隧道结调控的研究进展.首先讨论了多铁异质结构中电场对磁性的调控;之后介绍了电场调控磁化翻转的研究进展及理论上实现的途径;然后简述了电场对磁性隧道结调控的相关结果;最后在此基础上,对多铁异质结构中电场调控磁性及磁性器件进行了总结和展望.     

双层纳米磁电薄膜模型及分析

以层状磁电复合材料弹性力学模型为基础,建立了自由状态下双层纳米磁电薄膜的弹性力学模型,并以此为基础简单介绍了推导其磁电电压系数表达式的方法.计算了CoFe₂Ｏ₄/Pb（Zr_0．52Ti_0．48）Ｏ₃双层纳米复合薄膜的磁电电压系数理论值,分析结果表明基片对薄膜存在强烈的夹持效应,而且基片对压电与磁致伸缩两相材料间最佳体积比有一定的影响. 关键词： 磁电理论 磁电薄膜 铁电材料 磁致伸缩     

1-3型纳米多铁复合薄膜中电场诱导的磁化研究

运用Landau-Devonshire热力学唯像理论,考虑铁电相和铁磁相的电致伸缩、磁致伸缩效应以及产生于铁电/铁磁和薄膜/基底界面的弹性应力作用,两次重整介电和磁作用系数得到了这种多铁系统在Landau自由能函数下的本征二次方磁电耦合形式,从而研究了外延1-3型纳米多铁复合薄膜中极化、磁化随薄膜厚度、温度的变化以及该薄膜中外加电场诱导的磁化变化.结果表明薄膜平面内的应压力的弛豫使得磁化强度和极化强度随薄膜厚度的增加而减少,外加电场不仅能诱导铁电相极化场翻转,而且由于铁电和铁磁相界面竖直方向的弹性耦合导致 关键词： 多铁 磁电效应 磁致伸缩 薄膜     

K0.5Na0.5NbO3-LiSbO3-BiFeO3/CuFe2O4复合陶瓷的制备与磁电性能研究

采用传统的固相法制备了(1-x)(K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃)-xCuFe₂O₄ (x=0.1, 0.2, 0.3, 0.4) 磁电复合陶瓷, 并借助X射线衍射仪、扫描电镜和磁电耦合系数测试仪等对复合陶瓷的微结构和性能进行了分析. 结果表明, 复合陶瓷的K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃和CuFe₂O₄物相之间发生了一定的离子相互扩散作用, 且两相的颗粒大小匹配性较好. 随着CuFe₂O₄含量增加, 复合陶瓷的压电系数从130 pC/N减小到30 pC/N, 饱和磁致伸缩系数从4.5×10^-6增加到12.4×10^-6左右, 磁电耦合系数表现出先增加后减小, 在x=0.3时获得最大的磁电耦合系数9.4 mV·cm^-1·Oe^-1. 关键词： 0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃')" href="#">K_0.5Na_0.5NbO₃-LiSbO₃-BiFeO₃ 2O₄')" href="#">CuFe₂O₄ 磁电耦合     

Mn3TeO6 – a new multiferroic material with two magnetic substructures

From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin‐induced ferroelectricity and magnetoelectric coupling in Mn₃TeO₆ and observe two successive magnetic transitions at low temperatures. A non‐ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn₃TeO₆ is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Magnetoelectric effect in perovskite quantum paraelectric EuTiO3

On the basis of successful theoretical explanation of the observed large magnetic-field effect (by ∼7% with 1.5 T) on the dielectric constant below the Néel temperature T_N of 5.5 K, we have demonstrated convincingly the magnetoelectric effect in an antiferromagnetic quantum paraelectric EuTiO₃ system. The mutual control of electric and magnetic properties is revealed by the variation of the electric-field-induced polarization with applied magnetic fields as well as the change of the magnetic-field-induced spin moments under the control of electric fields. It is found that the applied electric field (magnetic field) acts like a fictitious magnetic field (electric field) on the EuTiO₃ system. The magnetoelectric susceptibility is deduced to be proportional to the product of the magnetization, electrical polarization, magnetic susceptibility and dielectric susceptibility.     

Specificity of magnetoelectric effects in a new GdMnO<Subscript>3</Subscript> magnetic ferroelectric

A complex study of the magnetic, electric, magnetoelectric, and magnetoelastic properties of GdMnO₃ single crystals has been performed in the low-temperature region in strong pulsed magnetic fields up to 200 kOe. An anomaly of the dielectric constant along the a axis of a crystal has been found at 20 K, where a transition from an incommensurate modulated phase to a canted antiferromagnetic phase, as well as electric polarization along the a and b axes of the crystal induced by the magnetic field H‖ b (H_cr ～ 40 kOe), is observed. Upon cooling the crystal in an electric field, the magnetic-field-induced electric polarization changes its sign depending on the sign of the electric field. The occurrence of the electric polarization is accompanied by anisotropic magnetostriction, which points to a correlation between the magnetoelectric and magnetoelastic properties. Based on these results, it has been stated that GdMnO₃ belongs to a new family of magnetoelectric materials with the perovskite structure.     

激发态电荷转移有机体的多铁性研究

随着人们对多铁性的深入了解,越来越多不同类型的有机多铁材料被合成出来.激发态电荷转移有机体的电荷转移网络是由一个提供电子的分子(给体donor,D~+)和一个接受电子的分子(受体acceptor,A~-)有序排列后构成的.D~+A~-长程有序排列,其激发态(激子)具有较长寿命和±1/2自旋,这是产生室温铁电性和铁磁性的根本原因.激发态容易受外场刺激,因此光照、磁场、电场、应力等能够很好地调控这类材料的铁电极化、磁矩和相应的磁电耦合系数.激发态电荷转移有机体不仅大大丰富了室温多铁材料体系,而且可以为开发新型多功能电子器件提供材料基础和技术储备.     

Magnetoelectric and magnetoelastic interactions in NdFe3(BO3)4 multiferroics

Complex experimental and theoretical investigations of the magnetic, magnetoelectric, and magnetoelastic properties of neodymium iron borate NdFe₃(BO₃)₄ along various crystallographic directions have been carried out in strong pulsed magnetic fields up to 230 kOe in a temperature range of 4.2–50 K. It has been found that neodymium iron borate, as well as gadolinium iron borate, is a multiferroic. It has a much larger (above 300 μC/m²) electric polarization controlled by the magnetic field and giant quadratic magnetoelectric effect. The exchange field between the rare-earth and iron subsystems (～50 kOe) has been determined for the first time from experimental data. The theoretical analysis based on the magnetic symmetry and quantum properties of the Nd ion in the crystal provides an explanation of the unusual behavior of the magnetoelectric and magnetoelastic properties of neodymium iron borate in strong magnetic fields and correlation observed between them.     

BaTiO_3/La_(0.67)Sr_(0.33)MnO_(3-δ)复合薄膜的磁致电极化和磁介电特性研究

采用脉冲激光沉积法制备了BaTiO_3(BTO)与缺氧的铁磁绝缘态La_(0.67)Sr_(0.33)MnO_(3-δ)(LSMO)构成的磁电复合薄膜,研究了20—300K温度区间内磁场对电极化特性和介电特性的影响.研究发现,施加磁场使得电滞回线的剩余极化强度和矫顽场均增大,其变化率峰值分别为111.9%和89.6%,峰值温度分别为40K和60K.异质结具有显著的磁介电效应,在测量温度区间内,磁场使得介电常数增大,介电损耗减小.在0.8T场强下,介电常数的最大磁致变化率出现在60K,达到了300%,而介电损耗也在此温度实现了最大变化,减小为零场时的50.9%.该磁电复合薄膜的磁致电极化和磁介电特性的极值均出现在LSMO层的磁电阻峰值温度附近,这说明磁场对电滞回线和介电参数的调制应该源自电荷相关的耦合作用.其可能的机理是磁场使得锰氧化物中的Mn离子局域磁矩趋于有序排列,并通过自旋-轨道耦合以及界面效应间接影响了BTO的电极化特性.研究结果对于多铁器件的开发和应用具有重要意义.     

Enhanced magnetization in Co and Ta-substituted BiFeO3 ceramics

Cobalt (Co) and tantalum (Ta) co-substituted BiFeO₃ polycrystalline ceramics were prepared by a solid-state reaction and their magnetic and dielectric properties were investigated. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. The co-substitution decreased the electrical conductivity by six orders of magnitude along with the reduction of grain size. The magnetoelectric coupling was estimated in co-substituted BiFeO₃ by determining the changes of the dielectric constant with an external magnetic field.     

Multiferroism in the dielectric function of CuO

The multiferroic properties of bulk CuO are manifested in the dielectric function which can be triggered by an external magnetic field h and by the temperature T. Within a microscopic model and a Green's function technique we have calculated the dielectric function \varepsilon ({\bf k};T,\;h). At the magnetic phase transition temperature T_{{\rm N}2} the dielectric function offers a pronounced anomaly. This kink disappears when the magnetic field is enhanced and \varepsilon ({\bf k};T,\;h) decreases with increasing h ‐field. Both properties are indications for a strong magnetoelectric coupling in this material. The observation of multiferroism in CuO within an analytical approach is achieved by considering frustration and a linear magnetoelectric coupling. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)