Session H27: Invited Session: McGroddy Prize, Adler Lectureship, and Pake Prize: Superconductivity and Spin Transport

Assembling, understanding, auguring phase diagrams for Fe-based superconductivity

The quest for improved examples of novel, potentially useful, superconductors reached another milestone in 2008 with the discovery of Fe-based superconductivity in wide range of structurally related arsenide and selenide compounds. In particular, the AFe$_{2}$As$_{2}$ (A = Ba, Sr, Ca) compounds proved to have the highly desirable combination of intriguing properties that imply intimate coupling between electronic, magnetic and structural degrees of freedom, exceptionally high and relatively isotropic upper critical field curves and readily grown, homogeneous single crystals. Over the past three years the CMP community has been able to develop a broad and deep empirical understanding of substitutional and pressure based phase diagrams of these materials that is leading to theoretical as well as synthetic insights. In this talk I will broadly review some of our key findings and speculate about future directions for research in this field.   

James C. McGroddy Prize for New Materials Lecture: New Superconductors and other Research in New Materials

Superconductors and other electronic materials can often display subtle relationships between their structural characteristics and their electronic properties. Though the primary interest in these relationships is within the condensed matter physics community, often at their foundation are the concepts of bonding and structure familiar to inorganic and solid state chemists. Thus a hybridized view, combining physics and chemistry, is one way of approaching the discovery and characterization of new materials. In this talk I will describe some of our research in this context and comment on some broader aspects of interdisciplinary research in new materials.   

David Adler Lectureship Award in the Field of Materials Physics: Racetrack Memory - a high-performance, storage class memory using magnetic domain-walls manipulated by current

Racetrack Memory is a novel high-performance, non-volatile storage-class memory in which magnetic domains are used to store information in a ``magnetic racetrack'' [1]. The magnetic racetrack promises a solid state memory with storage capacities and cost rivaling that of magnetic disk drives but with much improved performance and reliability: a ``hard disk on a chip''. The magnetic racetrack is comprised of a magnetic nanowire in which a series of magnetic domain walls are shifted to and fro along the wire using nanosecond-long pulses of spin polarized current [2]. We have demonstrated the underlying physics that makes Racetrack Memory possible [3,4] and all the basic functions - creation, and manipulation of a train of domain walls and their detection. The physics underlying the current induced dynamics of domain walls will also be discussed. In particular, we show that the domain walls respond as if they have mass, leading to significant inertial driven motion of the domain walls over long times after the current pulses are switched off [3]. We also demonstrate that in perpendicularly magnetized nanowires there are two independent current driving mechanisms: one derived from bulk spin-dependent scattering that drives the domain walls in the direction of electron flow, and a second interfacial mechanism that can drive the domain walls either along or against the electron flow, depending on subtle changes in the nanowire structure. Finally, we demonstrate thermally induced spin currents are large enough that they can be used to manipulate domain walls. \\[4pt] [1] S.S.P. Parkin, US Patent 6,834,005 (2004); S.S.P. Parkin et al., Science 320, 190 (2008); S.S.P. Parkin, Scientific American (June 2009). \\[0pt] [2] M. Hayashi, L. Thomas, R. Moriya, C. Rettner and S.S.P. Parkin, Science 320, 209 (2008). \\[0pt] [3] L. Thomas, R. Moriya, C. Rettner and S.S.P. Parkin, Science 330, 1810 (2010). \\[0pt] [4] X. Jiang et al. Nat. Comm. 1:25 (2010) and Nano Lett. 11, 96 (2011).   

George E. Pake Prize Lecture: Pulsed Laser Deposition and the Oxide Electronics Revolution

The discovery of the Pulsed Laser Deposition (PLD) Process at Bellcore was followed by a stream of advances in the epitaxial growth of oxides and a variety of heterostructures and interfaces. Today Oxide Electronics is a fascinating field with a great deal of new Science and potential for applications. Following a discussion of these events, my talk will focus on the adventure involved in creating a new company, Neocera, and, at the same time, pushing ahead in the evolving field of oxide electronics. There, electron spin, pairing, and alignment to create superconductivity and magnetism have opened up new frontiers for research and materials development.   

A New Avenue towards Colossal Magnetoresistance in Organic Tunneling Junctions

A major challenge for the field of organic spintronics is how to achieve large magnetoresistance (MR) in a reliable manner. We have developed a new approach that dramatically improves MR of organic spin valves. Our approach involves using buffer layer assisted growth to prepare magnetic nanodot layers on top of the organic spacer layer. Interdiffusion between magnetic electrode and organic spacer layer has been largely suppressed in devices prepared by this method. Consequently, devices become highly reliable and large magnetoresistance up to a few hundred percent has been obtained. Moreover, we have attempted to insert a single magnetic nanodot layer inside the organic spacer layer. In such a tunneling junction device, even when the electrodes are nonmagnetic, a colossal MR up to 100000\% has been achieved at relatively high temperatures. The underlying mechanism has been discussed based on temperature-dependent I-V curves and resistivity measurements.