Heteromolecular Interface Design for Better Multiferroic Molecular Spintronics

非技术性描述这个项目的重点是一类分子之间的接口是磁性的，但其中的磁性可以打开和关闭，和一组不同的分子，其性质很容易被电压改变。总体研究目标是更好地理解主导一类不寻常分子的电压操纵的机制，这些分子可以在磁性或非磁性之间翻转。我们有充分的理由去追求这种更好的理解。合适的分子组合，可以在像一个非常小的磁铁和一个没有磁性的状态之间切换，分子的内在属性可以通过施加电压来控制，这使得制造一个分子“开关”成为可能，它需要非常少的功率来打开和关闭。通过从每一类中选择合适的分子，可以制造出新颖、低成本和极低功率的电子器件，这些器件可以开关数十亿次而不会退化。这些设备可以缩小到病毒颗粒的大小，甚至更小，这可能导致超高密度的计算机存储器。成本低，因为分子膜可以印刷在各种表面上。研究人员开发了这项新技术，打算探索设计新颖甚至更好的分子材料的原理，其中磁性和电压交织在一起。学生培训将包括科学的直接国际经验。其他活动涉及本科生和研究生，包括访问本科生，在化学和物理学的接口和外展活动，学生学习如何沟通前沿研究的非技术观众的前沿研究。 技术描述这个研究小组已经展示了电压控制的非易失性晶体管类器件，使用分子自旋交叉复合物作为导电通道。在这些系统中，分子的自旋状态可以通过栅极电压来调节，从而以数量级改变磁性和电导。这一成功为深入了解分子系统中可能的磁电耦合打开了大门。本研究的重点是更好地了解这些金属有机配合物的自旋态的电压操纵的主导机制。研究铁电和局域矩分子系统的合适组合的最终目的是找到具有超大（对小磁场的大电响应）或超小（对小施加电压的大磁响应）磁电系数的系统。但这项研究的核心是分子间相互作用如何影响分子内构型，从而导致配体场、分子偶极以及最终自旋态的变化。为了实现这一目标，研究人员将（1）确定是什么决定了自旋交叉现象随分子膜厚度的变化;（2）确定自旋状态转换的能垒;（3）了解异质分子系统如何对竞争过程作出反应，其中分子覆盖层的自旋状态被施加的电场改变;（4）识别连续膜内的最小可控畴尺寸;以及（5）识别是否存在自旋取向各向异性势垒。组合的分子系统将通过各种光谱技术、磁力测量和扫描探针技术来表征，以确定自旋状态、铁电极化以及自旋交叉活化能，而薄膜异质结构电导和磁矩将在不同温度下的外加磁场和电场中表征。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，

Nontechnical DescriptionThis project focuses on the interface between a class of molecules which are magnetic, but where the magnetic properties can be turned on and off, and a different group of molecules whose properties are easily altered by voltage. The overall research goals are to better understand the mechanisms that dominate the voltage manipulation of an unusual class of molecules that can be flipped between being magnetic or not magnetic. There are good reasons to pursue this better understanding. Suitable combinations of molecules, that can be toggled between a state acting like a very small magnet and one having no magnetism, with molecules whose intrinsic properties can be controlled by an applied voltage make it possible to fabricate a molecular "switch" that requires very little power to turn on and off. By choosing the right molecule from each class, novel, low cost and extremely low power electronic devices can be made, that can be switched on and off billions of times without degradation. These are devices that can be reduced to the size of a virus particle, or even smaller, which could lead to super high dense computer memories. The cost is low since molecular films can be printed on a wide variety of surfaces. The investigators, having developed this new technology, intend to explore the principles for designing novel and even better molecular materials where magnetism and voltage are intertwined. Student training will include direct international experience in science. Other activities involve both undergraduate and graduate students, including visiting undergraduates, in cutting edge research at the interface of chemistry and physics and outreach activities where the students learn how to communicate cutting edge research to a nontechnical audience. Technical DescriptionThis research team has demonstrated voltage controlled nonvolatile transistor-like devices that use molecular spin crossover complexes as the conduction channel. In these systems, the molecular spin state can be tuned by the gate voltage, altering the magnetic properties and the conductance by orders of magnitude. This success opens the door to obtaining deeper insights into possible magneto-electric coupling in molecular systems. This research focuses on a better understanding of the mechanisms that dominate the voltage manipulation of the spin state of these metal-organic complexes. The ultimate aim of investigating suitable combinations of ferroelectric and local moment molecular systems is to find systems with super-large (large electric response to a small magnetic field) or super-small (large magnetic response to a small applied voltage) magneto-electric coefficients. But the core of this research is how intermolecular interaction affects intramolecular configurations, resulting in changes to the ligand field, the molecular dipole, and ultimately the spin state. To accomplish this goal, the investigators will (1) identify what determines the changes in spin crossover phenomenology with molecular film thickness; (2) determine the energy barriers to spin state switching; (3) learn how a heteromolecular system, where the spin state of the molecular overlayer is altered by an applied electric field, reacts to competing processes; (4) identify the smallest controllable domain size within a continuous film; and (5) identify whether or not a spin orientation anisotropy barrier exists. The combined molecular systems will be characterized by a variety of spectroscopic techniques, magnetometry and scanning probe techniques to determine spin state, ferroelectric polarization, as well as spin crossover activation energies, while thin film heterostructure conductance and magnetic moment will be characterized in the presence of applied magnetic and electric fields at various temperatures.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.