The Materials Research Science and Engineering Center (MRSEC) at The Johns Hopkins University (JHU) features one Interdisciplinary Research Group (IRG) with eight JHU participating faculty members from four Departments in the Krieger School of Arts and Sciences and the Whiting School of Engineering, as well as one researcher each from Brown University, Carnegie-Mellon University, and National Institute of Standards and Technology.

The Center focuses on the science and engineering of magnetoelectronics. The interplay of materials, nanostructures, and architectures that are essential for spintronics research necessitates interdisciplinary collaborations between researchers with complementary expertise. Nanostructures are a key component since the characteristic lengths for spintronic effects are typically one to few tens of nanometers. Indeed, controlling architecture within the nanostructure is essential for capturing new effects and realizing devices are based on the interplay between materials. The fabrication of new nanostructures requires an array of expertise and resources both in conventional thin film fabrication and processing, as well as in more specialized techniques such as soft-lithography and self-assembly.

Spin transport in nanostructures can be realized in vertical structures (e.g., CPP GMR and MTJs) with the current perpendicular to the interfaces, or in lateral structures through spin interconnects. New architectures for spintronics include nanorings, ultrathin lines spanning ferromagnetic contacts, and thickness-modulated half-metallic ferromagnets. Many of these issues are relevant to new and emerging technologies in spintronic devices, including magnetic random access memory, magnetic field sensors, and printable spin electronics. We have identified key scientific and engineering challenges that confront magnetoelectronics and have conceived new directions for exploration. All of these challenges and ideas address the common theme of spin-polarized transport in materials within nanostructures. For clarity, we organize the research into four closely linked thrust areas, summarized below. Progress in each of these areas benefits that of the others through new insights, new effects, and new architectures.

1. Perpendicular spin transport: We address critical issues in the newly discovered MgO-based tunnel junctions and in the spin torque effect. We study the physics of MgO devices, in particular the materials requirements and noise properties. Critical issues related to the spin torque effect, especially control of the switching current, will also be addressed. Combining spin torque with high magnetoresistance MTJs will lead to the prospect of devices that can be switched by a current.

2. Nanorings: Nanorings represent a new architecture for magnetoelectronics. We use self-assembly, soft-lithography, and surface functionalization to fabricate arrays of nanoring, including ordered arrays and positioning of individual rings. Both fundamental properties of magnetic nanorings and their integration into spintronic devices are being addressed. We are investigating individual single-component and multilayered rings, as well as the ensemble properties of large arrays.

3. Organic magnetoelectronic materials: Organic semiconductors offer an untapped resource for extending the field of magnetoelectronics. We are exploring spin injection, transport, and detection using organic semiconductors in conjunction with metallic ferromagnets. Our goal is to determine the design rules for the synthesis of organic spintronic materials that could provide the basis for hybrid metal/organic devices.

4. Lateral structures: We use lateral structures with novel architectures to study magnetoelectronic effects that are not accessible in conventional vertical structures. Among the novel structures that we employ are ultrathin wires spanning ferromagnetic contacts and thickness-modulated half-metallic ferromagnets. These structures are used to investigate spin transport properties in confined geometries, spin injection, and the influence of spin polarized currents on domain wall dynamics.

Seed Funding and Emerging Areas: We have in place a seed program for the incorporation of new researchers and new ideas that extend beyond the thrust areas. Seed proposals are solicited and funded annually. Junior faculty are given special consideration since seed funding is an effective way of nurturing them during the early stages of their careers and integrating them into the Center.

For more details on specific projects, go to Research Highlights.