University of Miami physicist develops battery using new source of energy

March 12, 2009

Researchers at the University of Miami and at the Universities of Tokyo and Tohoku, Japan, have been able to prove the existence of a "spin battery," a battery that is "charged" by applying a large magnetic field to nano-magnets in a device called a magnetic tunnel junction (MTJ). The new technology is a step towards the creation of computer hard drives with no moving parts, which would be much faster, less expensive and use less energy than current ones. In the future, the new battery could be developed to power cars. The study will be published in an upcoming issue of Nature and is available in an online advance publication of the journal.

The device created by University of Miami Physicist Stewart E. Barnes, of the College of Arts and Sciences and his collaborators can store energy in magnets rather than through chemical reactions. Like a winding up toy car, the spin battery is "wound up" by applying a large magnetic field --no chemistry involved. The device is potentially better than anything found so far, said Barnes.

"We had anticipated the effect, but the device produced a voltage over a hundred times too big and for tens of minutes, rather than for milliseconds as we had expected," Barnes said. "That this was counterintuitive is what lead to our theoretical understanding of what was really going on."

The secret behind this technology is the use of nano-magnets to induce an electromotive force. It uses the same principles as those in a conventional battery, except in a more direct fashion. The energy stored in a battery, be it in an iPod or an electric car, is in the form of chemical energy. When something is turned "on" there is a chemical reaction which occurs and produces an electric current. The new technology converts the magnetic energy directly into electrical energy, without a chemical reaction. The electrical current made in this process is called a spin polarized current and finds use in a new technology called "spintronics."

The new discovery advances our understanding of the way magnets work and its immediate application is to use the MTJs as electronic elements which work in different ways to conventional transistors. Although the actual device has a diameter about that of a human hair and cannot even light up an LED (light-emitting diode--a light source used as electronic component), the energy that might be stored in this way could potentially run a car for miles. The possibilities are endless, Barnes said.

"There are magnets hidden away in many things, for example there are several in a mobile telephone, many in a car, and they are what keeps your refrigerator closed," he said. "There are so many that even a small change in the way we understand of how they work, and which might lead to only a very small improvement in future machines, has a significant financial and energetic impact."

University of Miami

Submicrometer Sized Magnetic Tunnel Junctions
by Ulrich Klostermann (Author)

Engineering and characterization of aluminum oxide-based Magnetic Tunnel Junctions.
by Chengxiang Ji (Author)

Magnetic Tunnel Junctions (MTJs) consisting of two ferromagnetic layers separated by an insulator layer have attracted great interest due to their applications in magnetic read heads and potential applications in magnetic random access memory. Materials science plays an important role in the performance of the MTJs. The goal of this research was to focus on how the materials properties affect the tunneling magnetoresistance (TMR) of AlOx-based MTJs with (Co, Fe) electrodes. A method was developed to fabricate epitaxial (Co, Fe) (001) thin films on Si substrates using TiN buffer and a novel processing technique in order to achieve smooth interfaces between the electrode and the AlOx tunnel barrier. The (Co, Fe) thin films with other orientations, i.e. (110) and (211), were also grown on...

Density of states effects in nickel based magnetic tunnel junctions .
by Greg Michael McKusky (Author)

In the present work we report a study on two types of MTJs; one which uses Ni as one electrode and another using a high nickel content alloy for the electrodes. Our success with nickel stems from its large variation in the density of states in both the majority and minority spin bands near the Fermi energy. These large variations make it an appealing system to observe density of states effects. In what follows we will discuss our MTJ preparation techniques followed by a presentation of the experimental results. This is followed by a comparison of the experimental data to a simple theory of elastic tunneling which utilizes the density of states of the MTJ electrodes.

Handbook of Spin Transport and Magnetism
by Evgeny Y. Tsymbal (Editor), Igor Zutic (Editor)

In the past several decades, the research on spin transport and magnetism has led to remarkable scientific and technological breakthroughs, including Albert Fert and Peter Grünberg’s Nobel Prize-winning discovery of giant magnetoresistance (GMR) in magnetic metallic multilayers. Handbook of Spin Transport and Magnetism provides a comprehensive, balanced account of the state of the art in the field known as spin electronics or spintronics. It reveals how key phenomena first discovered in one class of materials, such as spin injection in metals, have been revisited decades later in other materials systems, including silicon, organic semiconductors, carbon nanotubes, graphene, and carefully engineered nanostructures. The first section of the book offers a historical and personal...

Organic Spintronics
by Zeev Valy Vardeny (Editor)

Present worldwide funding in organic electronics is poised to stimulate major research and development efforts in organic materials research for lighting, photovoltaic, and other optoelectronic applications. The field of organic spintronics, in particular, has flourished in the area of organic magneto-transport. Reflecting the main avenues of substantial advances in this arena, Organic Spintronics is an up-to-date summary of the experimental and theoretical aspects of the field. With contributions by a panel of international experts on the cutting edge of research, this volume explores: Spin injection and manipulation in organic spin valves The magnetic field effect in organic light-emitting diodes (OLEDs) The spin transport effect in relation to spin manipulation Organic...

Spin polarized current phenomena in magnetic tunnel junctions.
by Li Gao (Author)

Spin polarized current is of significant importance both scientifically and technologically. Recent advances in film growth and device fabrication in spintronics make possible an entirely new class of spin-based devices. An indispensable element in all these devices is the magnetic tunnel junction (MTJ) which has two ferromagnetic electrodes separated by an insulator barrier of atomic scale. When electrons flow through an MTJ, they become spin-polarized by the first magnetic electrode. Thereafter, the interplay between the spin-polarized current and the second magnetic layer manifests itself via two phenomena: (i) Tunneling magnetoresistance (TMR) effect. The relative alignment of the electrode moments determines the resistance and its change. This TMR effect is largely determined by the...

Magnetic Nanostructures (Springer Series in Materials Science)
by Bekir Aktas (Editor), Lenar Tagirov (Editor), Faik Mikailov (Editor)

This volume addresses the exciting and rapidly developing topic of ultrahigh-density magnetic data storage. It is the most advanced book on magnetic nanostructures, basics and applications. It combines modern topics in nanomagnetism with issues relating to the fabrication and characterization of magnetic nanostructures. This book will be of interest to R and D scientists and it provides an accessible introduction to the essential issues.

Nonvolatile Memory Design: Magnetic, Resistive, and Phase Change
by Hai Li (Author), Yiran Chen (Author)

The manufacture of flash memory, which is the dominant nonvolatile memory technology, is facing severe technical barriers. So much so, that some emerging technologies have been proposed as alternatives to flash memory in the nano-regime. Nonvolatile Memory Design: Magnetic, Resistive, and Phase Changing introduces three promising candidates: phase-change memory, magnetic random access memory, and resistive random access memory. The text illustrates the fundamental storage mechanism of these technologies and examines their differences from flash memory techniques. Based on the latest advances, the authors discuss key design methodologies as well as the various functions and capabilities of the three nonvolatile memory technologies.

Advances in Nanoscale Magnetism: Proceedings of the International Conference on Nanoscale Magnetism ICNM-2007, June 25 -29, Istanbul, Turkey (Springer Proceedings in Physics)
by Bekir Aktas (Editor), Faik Mikailov (Editor)

The book aims to provide an overview of recent progress in the understanding of magnetic properties in nanoscale through recent results of various theoretical and experimental investigations. The papers describe a wide range of physical aspects, together with theoretical and experimental methods. It is of central interest to researchers and specialists in magnetism and magnetic materials science, both in academic and industrial research, as well as advanced students.

Magnetic Heterostructures: Advances and Perspectives in Spinstructures and Spintransport (Springer Tracts in Modern Physics)
by H. Zabel (Editor), Samuel D. Bader (Editor)

Heterostructures consist of combinations of different materials, which are in contact through at least one interface. Magnetic heterostructures combine different physical properties which do not exist in nature. This book provides the first comprehensive overview of an exciting and fast developing field of research, which has already resulted in numerous applications and is the basis for future spintronic devices.