MAGNETOELECTRIC COUPLING IN FERROELECTRIC/FERROMAGNETIC HETEROSTRUCTURES: BEYOND VOLUME EFFECTS

铁电/铁磁异质结构中的磁电耦合：超越体积效应

• 批准号: 1101256
• 负责人: Shireen Adenwalla
• 金额: $ 38.5万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1101256&HistoricalAwards=false
• 关键词: MAGNETOELECTRIC; COUPLING; FERROELECTRIC; FERROMAGNETIC; HETEROSTRUCTURES

This proposal focuses on the direct (changes in ferroelectric polarization with applied magnetic field) and converse (changes in magnetic properties with electric field) magnetoelectric coupling in thin film heterostructures of organic ferroelectrics with transition metal and half-metal ferromagnets and the fabrication, characterization and testing of two prototype devices that exploit these effects. A sensitive low-magnetic-field sensor based on the direct magnetoelectric effect will provide an electrical output proportional to the magnetic field strength, and a non-volatile magnetic memory cell based on the converse magnetoelectric effect, with electric-field-assisted writing and an optical readout of the magnetic state will allow for the well-know advantages of electric rather than magnetic field writing. The large mismatch in stiffness coefficients between the soft polymer ferroelectric and the much stiffer ferromagnets enables the exploration of coupling effects that go beyond the strain driven coupling between magnetostriction and piezoelectricity. The two prototype devices will provide a proof-of-concept that will enable the development of devices that are not dependent on strain, resulting in lower material fatigue, and therefore increasing device longevity. Preliminary results on the direct effect in heterostructures of organic ferroelectrics with ferromagnetic top electrodes show ferroelectric polarization changes that are orders of magnitude too large to ascribe to strain effects alone, but are dependent on the strain gradients at magnetic domain walls changing the polarization via the flexoelectric effect. Studies of the converse effect will focus on the electric field induced effect driven by the spin dependent electric field screening at the surface of a ferromagnet. The ability to apply large electric field is greatly enhanced by the large displacement charge density D at the surface of the polymer ferroelectric. Preliminary results indicate that the high ferroelectric surface charge drives large changes in the magnetic anisotropy in thin Co films. The intellectual merit lies in the elucidation of novel interface coupling effects that, with careful design, have the potential to produce macroscopic changes in ferromagnetic or ferroelectric ordered materials. The ability to accurately attribute and quantify the coupling in these particular heterostructures will lead to a significantly improved ability to design heterostructures with large interfacial coupling effects, as well as the ability to understand how the coupling is driven, an understanding that is applicable to a wide range of interfaces between differently ordered materials. The broader impact lies in the potential for technological benefits from applications in data storage and sensors, as exemplified by the prototype devices mentioned above that will lead to novel methods for magnetic field sensing and for non-volatile magnetic data storage. All three PIs are committed to a wide variety of activities that promote teaching and learning beyond the UNL physics department. These include direct interactions with K-12, such as regular visits to elementary school classrooms, the mentoring of numerous undergraduate students, the development of effective teaching materials for teachers in K-12, the mentoring of student teacher pairs from underrepresented institutions through the MRSEC summer teacher fellowships and public outreach to museums and civic organizations.

该提案的重点是直接（铁电极化与外加磁场的变化）和匡威（与电场的磁性能的变化）磁电耦合薄膜异质结构的有机铁电体与过渡金属和半金属铁磁体和制造，表征和测试的两个原型设备，利用这些效果。 基于直接磁电效应的灵敏的低磁场传感器将提供与磁场强度成比例的电输出，并且具有电场辅助写入和磁状态的光学读出的基于匡威磁电效应的非易失性磁存储器单元将允许电场写入而不是磁场写入的众所周知的优点。 软聚合物铁电体和更硬的铁磁体之间的刚度系数的大失配使得能够探索超出磁致伸缩和压电之间的应变驱动耦合的耦合效应。这两种原型器械将提供概念验证，从而能够开发不依赖于应变的器械，从而降低材料疲劳，从而延长器械寿命。在异质结构的有机铁电体与铁磁顶部电极的直接影响的初步结果显示铁电极化的变化是数量级太大，单独归因于应变效应，但依赖于在磁畴壁的应变梯度通过挠曲电效应改变极化。匡威效应的研究将集中在铁磁体表面自旋相关电场屏蔽驱动的电场诱导效应。 聚合物铁电体表面的大位移电荷密度D大大增强了施加大电场的能力。初步结果表明，高铁电表面电荷驱动的薄Co膜的磁各向异性的大的变化。 智力上的优点在于阐明了新颖的界面耦合效应，经过精心设计，有可能在铁磁或铁电有序材料中产生宏观变化。 准确地归属和量化这些特定异质结构中的耦合的能力将导致显著改进的设计具有大界面耦合效应的异质结构的能力，以及理解如何驱动耦合的能力，这种理解适用于不同有序材料之间的宽范围的界面。更广泛的影响在于数据存储和传感器应用带来的潜在技术利益，如上文提到的原型设备所示，这些设备将导致磁场感测和非易失性磁性数据存储的新方法。 所有三个PI都致力于各种各样的活动，促进教学和学习超越UNL物理系。 其中包括与K-12的直接互动，如定期访问小学教室，指导众多本科生，为K-12的教师开发有效的教学材料，通过MRSEC夏季教师奖学金指导来自代表性不足的机构的学生教师对博物馆和民间组织的公共宣传。