09-05-2012, 10:31 AM
SPINTRONIC SCANNER FOR CANCER DETECTION
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INTRODUCTION:
An emerging research field in physics focused on spin-dependent phenomena applied to electronic devices is called spintronics. The promise of spintronics is based on manipulation not only of the charge of electrons, but also their spin, which enables them to perform new functions. Currently, the ability to manipulate electron spin is expected to lead to the development of remarkable improvements in electronic systems and devises used in photonics, data processing and communications technologies only. Now this paper brings out an innovative idea of extending the hands of spintronics in MEDICAL FIELD, in the detection of cancer cells even when they are very few in number in the human body.This approach is relied on two important aspects:
• the behavior of electron spin in a magnetic field
• the cancer cell’s abnormality over normal cells
SPINTRONICS:
Spintronics, or spin electronics, refers to the study of the role played by electron spin in solid state physics, and possible devices that specifically exploit spin properties instead of or in addition to charge degrees of freedom. In spintronics electron spin, in addition to charge, is manipulated to yield a desired outcome. An electron is just like a spinning sphere of charge. It has a quantity of angular momentum (its "spin") and an associated magnetism, and in an ambient magnetic field its energy depends on how its spin vector is oriented. Every electron exists in one of two states, namely, spin-up and spin-down with its spin either +1/2 or –1/2. In other words, an electron can rotate either clockwise or counterclockwise around its own axis with constant frequency. . Two spins can be "entangled" with each other, so that neither is distinctly up nor down, but a combination of the two possibilities. In order to make a spintronic device, the primary requirement is to have a system that can generate a current of spin polarised electrons, and a system that is sensitive to the spin polarization of the electrons. Most devices also have a unit in between that changes the current of electrons depending on the spin states.The simplest method of generating a spin polarised current is to inject the current through a ferromagnetic material. The most common application of this effect is a giant magnetoresistance (GMR) device. A typical GMR device consists of at least two layers of ferromagnetic materials separated by a spacer layer. When the two magnetization vectors of the ferromagnetic layers are aligned, then an electrical current will flow freely, whereas if the magnetization vectors are antiparrallel then the resistance of the system is higher. Two variants of GMR have been applied in devices, current-in-plane where the electric current flows parallel to the layers and current-perpendicular-to-the-plane where the electric current flows in a direction perpendicular to the layers
Spintronics (a neologism meaning "spin transport electronics", also known as , magnetoelectronics is an emerging technology that exploits the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices. They rely completely on magnetic moment of the electron. Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down".Electrons have a property that they occupy only one quantum state at a given time. To make a spintronic device, the primary requirements are a system that can generate a current of spin-polarized electrons comprising more of one spin species³up or down³than the other (called a spin injector), Spin process can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.
Advantages of spintronics
• Non-volatile memory.
• Performance improves with smaller devices.
• Low power consumption.
• Spintronics does not require unique and specialized semiconductors.
• Dissipation less transmission.
• Switching time is very less compared to normal RAM chips,spintronic RAM chips will:
Increase storage densities by a factor of three
• Have faster switching and rewritability rates smaller.
Limitations
• Controlling spin for long distances.
• Difficult to Inject and Measure spin.
• Interfernce of fields with nearest elements.
• Control of spin in silicon is difficult.
Historical Perspective
The research field of spintronics emerged from experiments on spin-dependent electron transport phenomena in solid-state devices done in the 1980s, including the observation of spin-polarized electron injection from a ferromagnetic metal to a normal metal by Johnson and Silsbee (1985), and the discovery of giant magnetoresistance independently by Albert Fert and
Peter Grünberg.The origins can be traced back further to the ferromagnet /superconductor tunneling experiments pioneered by Meservey and Tedrow, and initial experiments on magnetic tunnel junctions by Julliere in the 1970s. The use of semiconductors for spintronics can be traced back at least as far as the theoretical proposal of a spin field-effect-transistor by Datta and Das in 1990.
WORKING
Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down". To make a spintronic device, the primary requirements are a system that can generate a current of spin-polarized electrons comprising more of one spin species³up or down³than the other (called a spin injector), and a separate system that is sensitive to the spin polarization of the electrons (spin detector). Manipulation of the electron spin during transport between injector and detector (especially in semiconductors) via spin precession can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.Spin polarization in non-magnetic materials can be achieved either through the Zeeman Effect in large magnetic fields and low temperatures, or by non-equilibrium methods.