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Topic Name: Scientists are Trying to Amalgamate Magnetism and Magnetic Materials with Promising Electronic Materials such as Organic Semiconductors

Category: Mechanical

Research persons: Giovanni Vignale

Location: University of Missouri, Colombia

Details

A modern computer contains two different types of components: magnetic components, which perform memory functions, and semiconductor components, which perform logic operations. A University of Missouri researcher, as part of a multi-university research team, is working to combine these two functions in a single hybrid material. This new material would allow seamless integration of memory and logical functions and is expected to permit the design of devices that operate at much higher speeds and use considerably less power than current electronic devices.

Giovanni Vignale, MU physics professor in the College of Arts and Science and expert in condensed matter physics, says the primary goal of the research team, funded by a $6.5 million grant from the Department of Defense, is to explore new ways to integrate magnetism and magnetic materials with emerging electronic materials such as organic semiconductors. The research may lead to considerably more compact and energy-efficient devices. The processing costs for these hybrid materials are projected to be much less than those of traditional semiconductor chips, resulting in devices that should be less expensive to produce.

“In this approach, the coupling between magnetic and non-magnetic components would occur via a magnetic field or flow of electron spin, which is the fundamental property of an electron and is responsible for most magnetic phenomena,” Vignale said. “The hybrid devices that we target would allow seamless integration of memory and logical function, high-speed optical communication and switching, and new sensor capabilities.”

Vignale studies processes by which magnetic information can be transferred from a place to another.

“One of the main theoretical tools I will be using for this project is the time-dependent, spin-current density functional theory,” Vignale said. “It is a theory to which I have made many contributions over the years. The results of these theoretical calculations will be useful both to understand and to guide the experimental work of other team members.”

Note for Organic Semiconductor
An organic semiconductor is any organic material that has semiconductor properties. A semiconductor is any compound whose electrical conductivity is between that of typical metals and that of insulating compounds. Both short chain (oligomers) and long chain (polymers) organic semiconductors are known. Examples of semiconducting oligomers are: pentacene, anthracene and rubrene. Examples of polymers are: poly(3-hexylthiophene), poly(p-phenylene vinylene), F8BT, as well as polyacetylene and its derivatives.

There are two major classes of organic semiconductors, which overlap significantly: organic charge-transfer complexes, and various "linear backbone" polymers derived from polyacetylene, such as polyacetylene itself, polypyrrole, and polyaniline. Charge-transfer complexes often exhibit similar conduction mechanisms to inorganic semiconductors, at least locally. This includes the presence of a hole and electron conduction layer and a band gap. As with inorganic amorphous semiconductors, tunneling, localized states, mobility gaps, and phonon-assisted hopping also contribute to conduction, particularly in polyacetylenes. Like inorganic semiconductors, organic semiconductors can be doped. Highly doped organic semiconductors, for example Polyaniline (Ormecon) and PEDOT:PSS, are also known as organic metals.

Several kinds of carriers mediate conductivity in organic semiconductors. These include π-electrons and unpaired electrons. Almost all organic solids are insulators. But when their constituent molecules have π-conjugate systems, electrons can move via π-electron cloud overlaps. Polycyclic aromatic hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor.

In charge transfer complexes, even unpaired electrons can stay stable for a long time, and are the carriers. This type of semiconductor is also obtained by pairing an electron donor molecule and an electron acceptor molecule.

Organic semiconductors have many advantages, such as easy fabrication, mechanical flexibility, and low cost. Melanin is a semiconducting polymer currently of high interest to researchers in the field of organic electronics in both its natural and synthesized forms.

Note for Magnetic Field
In physics, a magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. Magnetic fields surround electric currents, magnetic dipoles, and changing electric fields.

When placed in a magnetic field, magnetic dipoles tend to align their axes to be parallel with the magnetic field, as can be seen when iron filings are in the presence of a magnet. Magnetic fields also have their own energy, with an energy density proportional to the square of the field intensity. The magnetic field is typically measured in either teslas (SI units) or gauss (cgs units).

There are some notable specific incarnations of the magnetic field. For the physics of magnetic materials, magnetism and magnet, and more specifically ferromagnetism, paramagnetism, and diamagnetism. For constant magnetic fields, such as are generated by stationary dipoles and steady currents.

The electric field and the magnetic field are tightly interlinked, in two senses. First, changes in either of these fields can cause ("induce") changes in the other, according to Maxwell's equations. Second according to Einstein's theory of special relativity, a magnetic force in one inertial frame of reference may be an electric force in another, or vice-versa. Together, these two fields make up the electromagnetic field, which is best known for underlying light and other electromagnetic waves.

In classical physics,the magnetic field is a vector field (that is, some vector at every point of space and time), with SI units of teslas (one tesla is one newton-second per coulomb-metre) and cgs units of gauss. It has the property of being a solenoidal vector field.

The field can be both defined and measured by means of a small magnetic dipole (i.e., bar magnet). The magnetic field exerts a torque on magnetic dipoles that tends to make them point in the same direction as the magnetic field (as in a compass), and moreover the magnitude of that torque is proportional to the magnitude of the magnetic field. Therefore, in order to measure the magnetic field at a particular point in space, you can put a small freely-rotating bar magnet (such as a compass) there: the direction it winds up pointing is the direction of ; and the ratio of the maximum magnitude of the torque to the dipole moment of the bar magnet is the magnitude.

The rotating magnetic field is a key principle in the operation of alternating-current motors. A permanent magnet in such a field will rotate so as to maintain its alignment with the external field. This effect was conceptualized by Nikola Tesla, and later utilised in his, and others, early AC (alternating-current) electric motors. A rotating magnetic field can be constructed using two orthogonal coils with 90 degrees phase difference in their AC currents. However, in practice such a system would be supplied through a three-wire arrangement with unequal currents. This inequality would cause serious problems in standardization of the conductor size and so, in order to overcome it, three-phase systems are used where the three currents are equal in magnitude and have 120 degrees phase difference. Three similar coils having mutual geometrical angles of 120 degrees will create the rotating magnetic field in this case. The ability of the three-phase system to create a rotating field, utilized in electric motors, is one of the main reasons why three-phase systems dominate the world's electrical power supply systems.

Note for Electron-Spin
Electrons, and other particles, have an intrinsic angular momentum, known as spin. This creates a magnetic dipole moment. When the electron is placed in a magnetic field, the intrinsic magentic dipole can align in one of two ways, parallel or anti-parallel to the field. The anti-parallel state is of lower energy. However, applying radiation of a certain frequency to the electron can raise it to the higher energy state, in which its magnetic dipole is parallel to the applied magnetic field. It will then fall back to the lower energy state, emitting a photon. If radiation continues to be applied, then the electron will "resonate" between the two energy states. This is known as electron spin resonance, and is used to identify compounds, which each have a unique spectrum of radiation absorption. This occurrence is used in both NMR and MRI.

Note for Fiber-Optic Communication
Fiber-optic communication is a method of transmitting information from one place to another by sending light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, the use of optical fiber has largely replaced copper wire communications in core networks in the developed world.

The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal using a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, and receiving the optical signal and converting it into an electrical signal.

Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance and high-demand applications. However, infrastructure development within cities was relatively difficult and time-consuming, and fiber-optic systems were complex and expensive to install and operate. Due to these difficulties, fiber-optic communication systems have primarily been installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. Since the year 2000, the prices for fiber-optic communications have dropped considerably. The price for rolling out fiber to the home has currently become more cost-effective than that of rolling out a copper based network. Prices have dropped to $850 per subscriber in the US and lower in countries like The Netherlands, where digging costs are low.

Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send into the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is typically digital information generated by computers, telephone systems, and cable television companies.

Optical fiber consists of a core, cladding, and a protective outer coating, which guides light along the core by total internal reflection. The core, and the lower-refractive-index cladding, are typically made of high-quality silica glass, though they can both be made of plastic as well. An optical fiber can break if bent too sharply. Due to the microscopic precision required to align the fiber cores, connecting two optical fibers, whether done by fusion splicing or mechanical splicing, requires special skills and interconnection technology.

Two main categories of optical fiber used in fiber optic communications are multi-mode optical fiber and single-mode optical fiber. Multimode fiber has a larger core (≥ 50 micrometres), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. However, multi-mode fiber introduces multimode distortion which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multimode fiber is usually more expensive and exhibits higher attenuation. Single-mode fiber’s smaller core (<10 micrometres) necessitates more expensive components and interconnection methods, but allows much longer, higher-performance links.

The research grant was awarded to the University of Iowa as part of a multi-university research initiative (MURI). Vignale joins Michael Flatté (University of Iowa), Andy Kent (New York University), Yuri Suzuki (University of California, Berkeley) and Jeremy Levy (University of Pittsburgh). John Prater of the Army Research Office will monitor the program.