Giant Magneto-Resistance - Research Paper Example

GIANT MAGNETORESISTANCE INTRODUCTION The first major discovery in spintronics was the development of the giant magnetoresistance (GMR) effect in1998. Conducting independent research, Albert Fert in France and Peter Grunberg in Germany discovered that in material composed of alternating layers of magnetic and nonmagnetic atoms, a minute change in the magnetic field is capable of producing a large change in electrical resistance. Using advanced nanotechnology related to micromechanics, they employed chemical techniques to produce layers of different materials only a few atoms thick. “In recognition of their contributions, Fert and Grunberg shared the 2007 Nobel Prize in physics” (Encyclopedia, 2009: 45905). The Giant Magnetoresistance effect was used in the development of data storage devices that were physically smaller but permitted increasingly more compact packing of the information content. Thesis Statement: The purpose of this paper is to investigate Giant Magnetoresistance (GMR) in multilayered films, determine its nature and examine its applications. THE RATE OF TECHNOLOGY DEVELOPMENT Intel Corporation’s cofounder Gordon Moore predicted in 1965 that the density of transistors in an integrated circuit would increase double every year. This observation became known as Moore’s Law; it was later amended to double every year and a half, which has proved to be a strikingly accurate prediction, over the last thirty years. The Moore’s Law gives rise to highly improved performance in electronics technology. With the generation of every new chip, transistors are reduced by a factor of 0.7. Each transistor occupies only half the surface area on the chip, as compared to the previous generation, can be switched in 30% less time, and requires only a third of the power for operation. Gordon Moore himself expects the law to sustain until around the year 2017, when insurmountable barriers founded on the laws of physics will bring to an end to increasing granularity of silicon-based technology. However, advancements in new fields such as quantum, optical and DNA computing may continue to provide increasing computing power at stable or falling prices, thus extending the effect of Moore’s Law significantly (Langabeer & Stoughton, 2001). Microprocessors are not the only high technology components showing this type of behaviour, a similar growth curve has been traced by computer memory (RAM: Random Access Memory). Hard drive (permanent memory/ storage) capacity has also increased while declining in price. “Since the first introduction of IBM’s magnetoresistive (MR) head technology in commercial products in 1991, real density of disk drives has increased by roughly 60% per year” (Langabeer & Stoughton, 2001: 8). More recent developments in MR head technology and giant magnetoresistance (GMR) have resulted in even higher growth rates in recent years. While these developments are of great benefit to the consumers of technology, there is a detrimental impact on manufacturers, who need to update their products in keeping with the technological advances. However, frequent updates in technology can mean difficulty for consumers also in keeping up with the latest available products. A general rule of thumb in the personal computer industry is that a there is a loss of value of a personal computer kept unused in inventory, at a rate of about 1% per week, due to the rapid pace of technological development. At the same time, product life cycles for high technology goods are generally much shorter than that of other industries, at times lasting only months. The attractiveness of a product to its targeted market may not allow for significant intervals for restocking, and opportunities for competition may be limited. Therefore, accurate anticipation of demand is crucial (Langabeer & Stoughton, 2001). GIANT MAGNETORESISTANCE (GMR) IN MULTILAYERED FILMS Magnetoresistance (MR) is the “fractional change in resistance of a material in the presence of a magnetic field” (Chaudhary et al, 2010: 13), and is a well-known physical phenomenon. Very high values of magnetoresistance MR (>10%) in epitaxial multilayers has redefined the effect as giant magnetoresistance (GMR). The origin of GMR is derived from the spin-dependent scattering of the conduction carriers within the magnetic layers or at the boundaries of the magnetic layers. Experiements confirm the predominance of spin-dependent scattering at the ferromagnet/ spacer layer interfaces. Giant magnetoresistance “has enabled engineers to increase the sensitivity of hard disk reading heads, and pack more data into less space” (Seppa et al, 2007: 229). Particular metals such as iron have atoms which work as small bar magnets, forming a line pointing in one direction. Further, electrons passing through these metals also have the potential to align according to the magnetic function of the metal, thus permitting the current to pass more easily. The Nobel Prize winning physicists Fert and Grunberg used this phenomenon along with another. The orientations of two layers of magnetic metal adjacent to each other tend to match since their magnetization turn. However, in case a layer of chromium or another nonmagnetic metal is placed between the two layers of magnetic metal, the magnetic flow of the two layers will face opposite directions. In order to orient the spins of the electrons adjacent to the magnetization of the first layer, the physicists passed a current through the layered formation. They believed that if the nonmagnetic layers were only a few nanometers thin, they would remain in the same orientation, when passing into the second magnetic layer. Since the orientation of the electrons would be opposite to the magnetization in the third layer, the resistance they face would be higher. Additionally, the physicists expected that by using an external force to compel the magnetization of the two external layers into the same direction, there would be a small decline in the resistance; it was found to be reduced by half. This confirmed the function of giant magnetoresistance (Seppa et al, 2007). The surprising large magnetic resistance that is activated permits the sensitive detection of a magnetic field. Initially it was IBM that used this new discovery in physical science, in their hard disks in 1997. Subsequently, giant magnetoresistance has increased hard disk-data densities thirty times. The new development is a significant one, since older readout technologies are coming to an end, causing a decline in the industry’s potential to store information in a particular surface area (Seppa et al, 2007). APPLICATIONS OF GMR IN MULTILAYERED FILMS Computer Memory, Data Storage, Photographic Imaging and Drugs In the digital field, enormous strides forward have been achieved in reducing the size and increasing the swiftness of microprocessors and memory devices. At present, integrated circuits of sub-micron size are being developed, using appropriate manufacturing processes. Therefore, significant changes are brought about by nanotechnologies in the method of producing electronic circuits. This is done by creating larger circuits from single atoms, instead of further reducing the size of atoms, and this method has beneficial results. The improved efficiencies are by a factor of millions. Various dimensions of life and the built environment are being transformed by the evolving potential of nanotechnology, which is without precedence. New discoveries in this field have given rise to highly viable businesses. Nanotechnology in several applications include “giant magnetoresistance for hard disk drives, nanolayers for data storage and photographic imaging industries, and nanoparticles for drugs in the pharmaceutical field” (Dean, 2002, p.25). Rapid Health Check with Giant Magnetoresistance Credit Card Gadget Credit card technology is based on the same principle of giant magnetoresistance used by computer drives for data processing. Fig.1. below depicts the device used for testing patients for numerous illnesses at once; it related to the credit card swiping device used for commercial purposes (Hagan, 2008). Figure 1. Giant Magnetoresistance Rapid Health Check Gadget (ScienceDaily, 2008) The machine scans a card with microscopic samples of blood, saliva or urine. It tests the samples “for a wide range of disease markers, chemicals usually given off by the immune system when the body is under attack” (Hagan, 2008: 51). Although still at a nascent stage, this new technique which uses non-invasive diagnosis of disease with wellness cards, has the capacity to examine minute samples for several diseases within a short time. After the machine identifies a health concern, the next stage of doctors’ investigating the case for administering treatment, follows. The machine works in the same manner as a computer hard drive, processing extensive information at extremely high speeds. The “disease markers are usually proteins or chemicals produced by the body when it is under attack or falling victim to an illness” (Hagan, 2008: 51), and they may differ for various diseases. The significant concept in this technology is the capability of carrying out a health check up swiftly, using only one rapid scan. The giant magnetoresistance rapid health check gadget identifies diseases by detecting the magnetic signature of viruses, bacteria or proteins. Each card has the capability to screen for disease markers for conditions including prostate cancer and herpes. It is expected to take a few additional years in developing the machine for the routine checking of patients’ health. Spintronics Spintronics or spin electronics refers to “the study and application of the extra degree of freedom of carriers such as electrons, which is their spin movement for the development of multifunctional and novel devices” (Chaudhary et al, 2010: 13). These devices include spin valves, magnetoresistive sensors, and according to Wetzig & Schneider (2006: 3) “read heads in hard disk drives, and magnetocouplers or nonvolatile magnetic random access memories (MRAM)”. An integration of different areas such as electronics, photonics, and magnetics will lead to the devices such as spin-FETs or field-effective transistors, spin-LEDs, spin-RTDs (resonant tunneling devices), optical switches operating at terahertz frequencies, modulators, etc. Recently, a biosensing device of a highly sensitive, giant magnetoresistance spin valve (GMR-SV), with high linearity and very low hysteresis was produced by photolithography. Even one drop of human blood and nanoparticles in distilled water was sufficient for their detection and analysis (Zhang et al, 2009). Spintronic devices require materials which can use the spin of charge carriers, either through giant magnetoresistance (GMR), through room temperature ferromagnetism (RTFM), or tunnel magnetoresistance (TMR), and sustain the spin polarization in the required fashion. This has compelled a world-wide research impetus to look for materials which either exhibit high values of GMR/ TMR or show stable and intrinsic ferro-magnetic ordering at room temperature. Both the effects: GMR/ TMR and RTFM are characteristic of certain magnetic nanomaterials and their multilayers. The nanotechnology based on GMR led to sensitive readout heads for compact hard disks, a significant revolution in the area of information technology (Chaudhary et al, 2010). Giant Magnetoresistance Sensors The properties of the solid state thin film sensors and the IC-compatible fabrication are such that, the GMR-biosensors can be integrated into a very high density. Therefore, such a GMR sensor array would be suitable for multianalyte biodetection (Varadan et al, 2008). Spintronic giant magnetoresistance bridge sensors: A photomicrograph of a typical GMR magnetic sensor/ magnetometer is given below, Fig.2. (NVE Corporation, 2008). Figure 2. Giant Magnetoresistance Magnetic Sensor (Magnetometer) (NVE Corporation, 2008) The manufacturing steps are composed of: vacuum depositing of the thin metal-alloy films onto silicon wafers, thermal annealing, magnetic annealing, and photolithography. Usually, GMR resistors are designed into serpentine resistors using photolithography. When the sensor is activated, the serpentine pattern maximises resistance per unit area, thereb minimising power consumption when the sensor is sampled (NVE, 2009). In a commonly used sensor, four GMR resistors are arranged as a Wheatstone bridge. A bridge configuration provides an easy to use voltage output that is both sensitive to any changes in voltage output and is also proportional to the magnetic field applied. Among the four resistors, two are for sensing and the other two are reference resistors. The reference resistors are shielded by a magnetic covering composed of nickel-iron that measures 0.0004 inches in thickness. The sensing resistors which are exposed reduce their electrical resistance in response to an external magnetic field. The reference resistors, however, remain unchanged, creating a voltage at the bridge output. The covering or shield may also function as a flux concentrator for the sensing resistors, thereby raising the level of sensitivity of the device and increasing its spacial specificity. The small geometries of spintronic sensors would cause flux concentration to be effective, and hence increase sensitivity up to a factor of 100 (NVE, 2009). CONCLUSION This paper has highlighted giant magnetoresistance (GMR) in multilayered films, examined its nature and discussed its applications. Besides computer memory, data storage, photographic imaging and pharmaceutical drugs, other applications are: rapid health check by giant magnetoresistance credit card gadget, and spintronic devices such as giant magnetoresistance magnetic sensors. The contemporary era of advanced nanotechnology is a new field in technology, science and materials at the molecular level (Deal 2002). In the new millennium materials processing is based on breakthrough developments in nanotechnology. Engineers and scientists are working towards a time when materials and devices can be fabricated at the atomic or molecular level. On the other hand, high technology industries are going through a rough time aligning consumer demand with networked supply chain. Improving the forecasting and planning process can be achieved if the demand forecasting processes are “collaborative, sophisticated, oriented towards the product life cycle, and developed using non-constrained consumer demand data” (Langabeer & Stoughton, 2001: 10). REFERENCES Chaudhary, S., Pandya, D.K. & Kashyap, S.C. (2010). Advanced magnetic materials for spintronics. Retrieved on 2nd December, 2010 from: http://www.iitd.ac.in/Advancedmaterials/Advance%20Magnetic%20Materials%20for%20Spintronics.pdf Deal III, Walter F. (2002). Under the microscope: Nanotechnology. Nanotechnology, nanoscience, and nanoengineering focus on the design and manipulation of individual atoms to produce tailor-made products and devices. The Technology Teacher, 62 (1): pp.21-25. Encyclopedia (2009). Spintronics. Giant Magnetoresistance. The Columbia Encyclopedia, 6th Edition, New York: Columbia University Press. Hagan, P. (2008). Credit card that knows everything about your health. The Daily Mail. November 4, 2008. p.51. Retrieved on 30th November, 2010 from: http://www.questia.com/read/5030077411 Langabeer, J. & Stoughton, T. (2001). Demand planning and forecasting in the high technology industry. The Journal of Business Forecasting Methods and Systems, 20 (1): pp.7-10. NVE Corporation. (2008). Spintronic GMR bridge sensors. How GMR works. Retrieved on 30th November, 2010 from: http://www.gmrsensors.com/gmr-operation.htm ScienceDaily. (October 29, 2008). Toward non-invasive disease diagnosis with wellness cards. ScienceDaily. Retrieved on 2nd December, 2010 from: http://www.sciencedaily.com/releases/2008/10/081027112944.htm Seppa, N., Castelvecchi, D. & Williams, S. (October 13, 2007). Mice, magnetism, and reactions on solids: Nobels awarded in genetics, materials science, and surface chemistry. Science News, 172 (15): p.229. Varadan, V.K.,, Chen, L. & Xie, J. (2008). Nanomedicine: Design and applications of magnetic nanomaterials, nanosensors and nanosystems. The United Kingdom: John Wiley and Sons. Zhang, X., Guo, Q. & Cui, D. (2009). Recent advances in nanotechnology applied to biosensors. Sensors, 9: pp.1033-1053. Read More