Spin Polarized Transport Properties in Tunnel Structures

University Of Delaware, Newark DE

Investigators

Abstract

Two vital scientific areas with important technological prospects involve spin transport in tunneling structures made of metals and semiconductors. The fabrication of magnetic tunnel junction heterostructures is becoming a mature technology, and yet there still remain important scientific issues related to the bias dependence of the tunneling magnetoresistance, noise, and structure-property relationships. This individual investigator award supports a project that focuses on developing a thorough understanding of spin-polarized tunneling transport. The studies involve: applying electron holography to profile the tunnel barrier; investigating, both in theory and in experiment, how the density-of-states, the barrier height, and the barrier shape affect the bias dependence of the tunneling magnetoresistance; examining the interplay among different length scales arising from charge and spin transport; using noise spectroscopy to probe magnetization reversal and fluctuations, defects in the tunnel barrier, and the distribution of conductance channels in the barrier; and developing room temperature ferromagnetic semiconductors. These issues directly impact the technological prospects of using tunnel junction structures for nonvolatile magnetic random access memory and field sensing applications, such as magnetic recording read heads and biological assays that use magnetoresistive sensor arrays. In view of this, the PIs maintain collaborations with industry. The program also aims to bring relevance to science education where two distinct needs have become apparent. The first is that higher education must address explicitly the issue of transferable job skills in the curriculum. The second is the importance of science and magneto-electronic technology to U.S. competitiveness and economic growth. These two needs will be addressed in a program that spans local, regional, and international levels. Modern technological advances in nanofabrication methods and heteroepitaxy have greatly invigorated the investigation of magnetism and are providing the capability to engineer magnetic phenomena at the nanoscale. New fields of basic research have also emerged - a notable example is "spin-electronics" or "spintronics". Applications of these advances are enabling the creation of entirely new magneto-electronic device structures and driving the development of a revolutionary new class of electronics based on electron's spin (a quantity related to electron's magnetic behavior) in addition to, or in place of, electronic charge. Two vital scientific areas with important technological prospects involve spin transport in metallic tunnel junction systems and semiconductors. In this proposal, we concentrate on developing a thorough understanding of spin-polarized tunneling transport through a synergistic combination of: a novel microscopy technique used to reveal how the properties of the tunnel barrier affect a device's resistive response to an applied magnetic field (magnetoresistance); examining the interplay among different length scales arising from charge and spin transport; using noise spectroscopy to probe magnetization reversal and fluctuations, defects in the tunnel barrier, and the distribution of conductance channels in the barrier, and developing room temperature ferromagnetic semiconductors. These issues directly impact the technological prospects of using tunnel junction structures for nonvolatile magnetic random access memory and field sensing applications, such as in magnetic recording read heads. In view of this the PIs collaborate with leading industries towards optimizing device performance. The program also aims to bring relevance to science education. Two distinct needs have become apparent. The first is that higher education must address explicitly the issue of the role of transferable job skills in the curriculum. The second is the importance of science and magneto-electronic technology to U.S. competitiveness and economic growth. These two needs will be addressed in a program that spans local, regional, and international levels.