Study of Multiferroic Tunnel Junctions

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。多铁性隧道结是指使用铁电绝缘体势垒的铁磁隧道结。理论计算表明，铁电极化反转将导致隧道结中的电阻开关行为。此外，铁电层和铁磁层之间的相互作用可以影响势垒的电极化，界面处的电子结构和磁性，以及隧穿电流的自旋极化。因此，这种类型的结可以显示新的功能，如四进制或八进制逻辑状态，可以通过磁场和电场进行编码。它还可以开辟新的方法来潜在地控制自旋极化。然而，要在夹在两个铁磁层之间的纳米厚铁电层中保持铁电性是非常具有挑战性的，并且以前还没有实现可靠的多铁性结。这项个人研究奖支持一项研究计划，以制造和系统地研究锰氧化物/Ba 1-xSrxTiO 3/锰氧化物和锰氧化物/Ba 1-xSrxTiO 3/Co结构中的多铁性隧道结。该项目的目标是首先建立这种结在电场和磁场下的行为，然后系统地研究电场和磁场对不同状态的操纵。该项目将为研究生和本科生，包括妇女和代表性不足的少数民族，提供一个刺激的环境，在物理学，材料科学和设备制造和测试的跨学科经验。非技术摘要该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。磁隧道结的最新进展使得这些器件可以用于计算机读取头、磁传感器和非易失性磁随机存取存储器。隧道结由两个金属层和其间的纳米厚绝缘体层或阻挡层组成。理论上预测，通过使用非常薄的铁电绝缘体-一种具有自发电荷极化的材料，可以通过电压切换-作为屏障，可以实现新的功能。例如，它可以显示可以由磁场和电场编码的四元逻辑状态，而不是当前磁性隧道结中的二进制状态。这对量子信息处理非常重要。铁磁层和铁电层之间的强相互作用还可以导致对自旋极化的电控制，这是实现功能性自旋电子器件的关键进展，功能性自旋电子器件是依赖于自旋极化输运而不是传统电子输运的新器件概念。然而，要在纳米厚的材料中实现电荷极化是非常具有挑战性的，并且这种结以前还没有被制造出来。该奖项支持一项研究计划，以锰氧化物为电极，钛酸锶钡为绝缘体，制造和系统地研究几种这样的结结构。 该项目的目标是首先制造结，然后系统地研究结的特性以及如何通过使用电场和磁场来操纵不同的状态。该项目将为研究生和本科生，包括妇女和代表性不足的少数民族，提供一个刺激的环境，在物理学，材料科学和设备制造和测试的跨学科经验。

Technical AbstractThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Multiferroic tunnel junction refers to a ferromagnetic tunnel junction using a ferroelectric insulator barrier. Theoretical calculations have shown that the ferroelectric polarization reversal will result in resistance switching behavior in a tunnel junction. Furthermore, the interplay between the ferroelectric and ferromagnetic layers can affect the electric polarization of the barrier, the electronic structures and the magnetic properties at the interface, and the spin polarization of the tunneling current. This type of junctions can thus display new functionalities, such as quaternary or octal logic state, which can be encoded by both magnetic and electric fields. It can also open up new ways to potentially control spin polarization electrically. However, to preserve ferroelectricity in a nanometer thick ferroelectric layer sandwiched between two ferromagnetic layers is extremely challenging and reliable multiferroic junctions have not been achieved previously. This individual investigator award supports a research plan to fabricate and systematically study the multiferroic tunnel junctions in manganite/Ba1-xSrxTiO3/manganite and manganite/Ba1-xSrxTiO3/Co structures. The objective of the project is to first establish the behaviors of such junctions under electric and magnetic fields, and then to systematically study the manipulation of the different states by both electric and magnetic fields. The project will provide both graduate and undergraduate students, including women and underrepresented minorities, with a stimulating environment for interdisciplinary experience in physics, materials sciences, and device fabrication and testing. Non- Technical AbstractThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Recent advances in magnetic tunnel junctions have made it possible to use these devices in computer read head, magnetic sensors, and non-volatile magnetic random access memories. A tunnel junction consists of two metal layers and a nanometer thick insulator layer or barrier in between. It was predicted theoretically that by using a very thin ferroelectric insulator--a material with a spontaneous charge polarization which can be switched by an electrical voltage--as the barrier, new functionalities can be achieved. For example, it can display quaternary logic states which can be encoded by both magnetic and electric fields, instead of the binary states in the current magnetic tunnel junctions. This could be very important for quantum information processing. The strong interaction between the ferromagnetic layer and the ferroelectric layer can also lead to control of the spin polarization electrically, which is a critical advance in achieving functional spintronic devices, a new device concept that relies on the spin polarized transport instead of the conventional electron transport. However, to achieve charge polarization in a nanometer thick material is extremely challenging and such junctions have not been made previously. This award supports a research plan to fabricate and systematically study several such junction structures using manganite as the electrode and Barium Strontium titanate as an insulator. The goal of the project is to first fabricate the junctions, and then to systematically study the junction properties and how to manipulate the different states by using electrical and magnetic fields. The project will provide both graduate and undergraduate students, including women and underrepresented minorities, with a stimulating environment for interdisciplinary experience in physics, materials sciences, and device fabrication and testing.