Survey on Giant Magneto-resistance - Research Paper Example

Running head: GIANT MAGNETO-RESISTANCE Research Survey on Giant Magneto-resistance (GMR) Abstract This paper is a research survey and collection of documented reports about the Giant Magneto-resistance or GMR. This paper is intended to give more clarification and explanation about the nature and applications of GMR as a promising development in information technology and also its promising support to spintronics. Giant Magneto-Resistance Introduction The Giant Magneto-resistance or GMR is the ‘quantum mechanical magneto-resistance effect displayed among thin, multi-layered film structures (Carbone et. al., 1987).’ Moreover, it is composed of alternating ferromagnetic and non-magnetic layers (Grünberg et. al., 1986). On year 2007, Peter Grünberg and Albert Fert discovered the GMR; in so doing, they were awarded with the Nobel Prize in Physics. The GMR effect displays a significant change in electrical resistance which depends on the parallel or anti-parallel alignment of its adjacent ferromagnetic layer’s magnetization. For parallel alignment, overall resistance is low; whereas, antiparallel alignment signifies high resistance (Hinchey et. al., 1986). Due to the increasing usage of faster, smaller, much-improved and capable but cheaper computers as an advancement of technology, the insistent demand for the development of sensors and hard drives (devices for sensing and storing information) arises. A decade ago, researchers achieved the discovery of the Giant Magneto-resistance (GMR); and so, they came up with developing sensors (GMR) used for the purpose of reading the data bits which are coded on disk drives and which are bests described as the tiny, magnetized regions. Giant Magneto-resistance are sensors with high sensitivity which is used to read heads leading to magnetic fields and that which allows bit size reduction and therefore, increases the magnetic hard disk drive’s storage capacity (Science Week, 2005). The Discovery of GMR On year 1988, a research committee (European researchers), have found that there are huge changes which occur on thin-layered materials made of metal as it responds to small magnetic field. Initiated by Peter Grünberg (of Forschungszentrum Jülich (DE), GMR (in trilayers Fe, Cr, Fe) was first discovered. On the other hand, GMR was also discovered independently by Albert Fert’s team, in University of Paris. The latter group (Ferts’s) observed the large, significant effect among multilayers which led to its name; and the first (1) group (Grünberg’s) accurately debriefed about its underlying Physics explanation. Therefore, the discovery of GMR, presents a new phenomenon on Physics which led to the development and application of hard disk memory storage or IBM; together with MRAM, also known as Magnetic Random Access Memory and a new field of electronics, Spintronics (those devices which derives its power source from the spins of electrons). Moreover, the development of MRAM and Spintronics are still in continuous progress (Varadan et. al., 2008). Composition of GMR Giant Magneto-resistance is comprised of 2-layers of ferromagnetic material such as cobalt (Co) and thin-layered normal metal, copper (Cu). Current flows when magnetic phenomenon occurs for the parallel alignment of ferromagnetic layers, resulting to existence of little resistance. In case two layers become antiparallel, it results to higher resistance (Hinchey et. al., 1986). Definition and Applications of GMR Presently, Giant magneto-resistant devices or the magneto-resistance is referred to as: ‘the percentage difference between the parallel and antiparallel configurations’ which around ten to fifteen percent (10-15%). On application, the usual direction of such magnetization of the ferromagnetic layer is fixed. The other layer’s direction therefore, is determined by external field—on data bit. Significantly, a magneto-resistant device (particularly, the GMR, functions to detect the direction of the other layer’s magnetic field through its effect or result on resistance and the current flowing through it (Hinchey et. al., 1986). The other way to understanding Giant magneto-resistance (GMR) is to present is as the ‘change of electrical resistance produced in a current-carrying conductor or semiconductor on application of a magnetic field (H)’ (Varadan et. al., 2008). One of the Galvanomagnetic effects of this GMR phenomenon was observed when magnetic field (H) is parallel and oblique to current flow. On high fields, change of resistance rises faster than magnetic field doubled or (H2) and it increases on linear direction with magnetic field (H) but on smaller fields, change of resistance is the usual proportional direction for H2. Further, non-magnetic solids are mostly observed as having a magneto-resistance which is positive (Varadan et. al., 2008). Understanding Electrons, Magnetic Field and GMR By recalling significant attributes of electrons (particles that are negatively charged having small mass and can carry current passing thru metal wire), electrons do have a spinning property. In fact, an electron, when charged, spins and generates magnetic field to the direction opposite of the electron’s spin. On the other hand, if electrons within objects spin on the same direction, this is when the objects become magnetic on itself, and thus, their magnetic field cancelled (Varadan et. al., 2008). Magnetic Tunnel Junction in comparison to GMR devices In the recent technology emerges the Magnetic Tunnel Junction (MTJ), which is possible a component of every hard drive created by manufacturers. It consists of a tunnel-junction sensor which is on progress. In comparison to GMR devices, MTJ is more promising with its higher sensitivity features. Recent experiment findings support that MTJs are very promising (Grünberg et. al., 1986). Consisting of 2-layered ferromagnetic material, MTJs are even isolated by another insulating layer. The electrons in one layer should underpass through that insulating layer in order to reach the other part or layer. Moreover, the current underneath flows readily when such ferromagnetic materials are parallel or in other words, aligned rather than when the ferromagnetic moments are misaligned or antiparallel (Hinchey et. al., 1986). In 1975, research findings on the topic about tunnel junctions proved that tunnel junctions are dependent on the related magnetic directions of two (2) ferromagnetic electrodes. On the other hand, Meservey & Tedrow initiated the studies on spin-polarized tunnelling; however, the attempt to yield high tunnelling magneto-resistance resulted to become unsuccessful. Yet, in 1995, the interest about the topic was revived when research committee led by Jagadeesh Moodera came up with TMR values = 17 percent. Further, another team led by Terunobu Miyazaki (Tohoku University) contributed for more results about the topic. Since then, TMR values increased and reached its 70 percent on January 2004 (ScienceWeek, 2005). On Magnetic and Non-magnetic Layers, and Applications of GMRs According to scientists, changes in the resistance of materials could be observed whenever magnetic field was introduced to the alternating non-magnetic and magnetic layers. As mentioned earlier, resistance is high when electrons of various magnetic layers spin on antiparallel directions (See figure 1 below); whereas, low resistance results from electrons which spin on a parallel direction and causes a drop in resistance. These magnetic, layered materials are better known as the Giant magneto-resistance materials or again, GMRs (Grünberg et. al., 1986). Nowadays, modern hard drives are made up of an engineered nanomaterial which contains GMR. On applications, GMRs may be useful for motion sensors or detectors, current transformers, automotive antilock breaks, and etc. What makes GMR exceptional among its former predecessor devices was its higher sensitivity and smaller features as compared to previous, similar, sensors or devices (Varadan et. al., 2008). Better illustration is shown below to understand GMR and its composition of magnetic and non-magnetic metals/layers: Figure 1: GMR materials made from alternating layers of non-magnetic and magnetic layers of metals that are nanometers in its thickness. More Applications of GMR Surprisingly but true, the use of GMR in nanomedicine technology could also be applied. Current developments on nano-medicine offer innovative procedures and approaches for treatment, prevention, and even the early onset diagnosis of some fatal illnesses. Recent development on nanotechnology which involves magneto-resistant materials in its composition includes magnetic nanomaterials, magnetic nanosensors, and magnetic nanoparticles. These nanomagnetic materials are available commercially and are continuously increasing its usage across the globe (Grünberg et. al., 1986). Going back to our original topic about GMR, below are articles to understand more about Giant Magneto-resistance and spin valves as a relative concept: Materials Science: Giant Magneto-resistance, TMR, and Spin Valves "Magneto-resistance" is a term which refers to ‘a change in the electrical resistance of a conductor or semiconductor upon the application of a magnetic field, a property of certain systems. Giant magneto-resistance is a quantum mechanical effect observed in magnetic thin-film structures composed of alternating ferromagnetic and nonmagnetic layers’ (Grünberg et. al., 1986). Here are some points contributed by Z.H. Xiong and research committee: They operationally defined “spin valve” as ‘a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field (Science Week, 2005).’ They also contributed on the discoveries and developments of topics on Giant magneto-resistance (GMRs), Tunelling Magneto-resistance (TMRs occurring in metallic spin valves where its revolutionized applications are used for memory, and magnetic recording; third, is their contribution of spin electronics or “Spintronics.” Intensive researches are now devoted on several attempts to find out the effects of spin-dependent on semi-conductor materials (Science Week, 2005). Although there is already recent developments on detectors and spin injections using inorganic semiconductors, spin valve (devices) that contains semi-conducting spacers are not yet demonstrated. Relatively, Pi-conjugated semi-conductors offer an alternative approach to semi-conductor spin electronics (spintronics) and it is promising due to its characteristics of huge spin coherence and strong electron-phonon coupling (Varadan et. al., 2008). Considered as a “new class” of electronic materials, these pi-conjugated organic semi-conductors (OSEs) are significant on various technology applications that ranges from information display and large area electronics; it generates its ability to process economically in large areas, its tunability of electronic properties, its compatibility with processing on a low-temperature basis, and its characteristic of simplicity with regard to its thin filmed, device fabrication (ScienceWeek, 2005). The immeasurable flexibility of (synthetic organic chemistry) allows the development of pi-conjugated (OSE) structures. With the conventional, inorganic semi-conductors, OSE structures functions with an unattainable degree of control. Furthermore, OSEs are characterized by having extreme, weak spinning orbit and also hyperfine interaction—making the spin of electrons diffuse on a lengthy mechanism. However, the mentioned characteristics of OSEs allow itself to make way for transport applications and inducting spin-polarized electron injection (Science Week, 2005). Low temperature giant magneto-resistant effects extended to as large as 40 %, according to Z.H. Xiong et al., as they report on the transportation, detection, and injection of spin polarized carriers using organic semi-conductor to functionas a spacer layer inside a spin-valve structure. In addition, the researchers have preferred using 8-hydroxy-quinoline aluminium (alq3) which is a small, pi-conjugated molecule and is mostly used for organic light emission diodes (OLEDs), the molecule therefore, serves as ‘OSE spacer” in organic spinning valves, for the reason that it could be deposited easily like thin films combined with various metallic electrodes (Varadan et. al., 2008). Consisting of three layers, the vertical organic (fabricated) spin-valves are composed of one OSE spacer and two (2) FMs (FM1 and FM2) or ferromagnetic electrode films. By manufacturing two (2) FM electrodes that have different, coercive fields namely, Hc1 & Hc2, their magnetic directions could either have a parallel or antiparallel direction or alignment configuration when sweeping external, magnetic field (H). These magnetic directions are significant for proving spin-valve effect (Science Week, 2005). On recommendation, Z.H. Xiong and the other researchers suggest that their study demonstrates spin-polarized carrier injection, detection, and transport which composes spin electronics (spintronics) which can be attained using a pi-conjugated OSE. This includes the authors suggestions of new and different applications in organic spin electronics (spintronics) like spin OLEDs—powered by the useful function of OSEs (Varadan et. al., 2008). On Magneto-Electronics An apparent approach to electronics emerges based on the up, down, or spin of the carriers instead of the usual holes or electrons used as a traditional semi-conductor devices on electronics. In brief, the physical basis which explains the phenomenon of such observed effects is therefore called as the ‘Giant Magneto-resistance’ or the GMR (Varadan et. al., 2008). In addition, Gary A. Prinz (1998) contributed the following points on the related topic about the research for GMR: The Effect of Giant Magneto-resistance Prinz (1998) referred and operationally defined Giant Magneto-resistance as: ‘a quantum mechanical effect observed in magnetic thin-film structures composed of alternating *ferromagnetic and nonmagnetic layers.’ Relative to the earlier text, he also observed ferromagnetic layers or magnetic moments that when the current flow was parallel, there exists a minimization of the dependent scattering of carriers and results to the occurrence of lowest resistance. But that also made Prinz explain that when ferromagnetic layers are anti-parallel or not aligned, there exists the opposite or the maximization of spin-dependent scattering of carriers and that which achieve its highest resistance. The magnetic moments of ferromagnetic layers and its direction are therefore manipulated by magnetic fields present (H) and applied to the materials. When charged, these materials could then be manufactured to create significant or large changes in the resistance as it responds to small magnetic fields and as it operates in a condition where room temperature also plays a significant role or effect on the latter (Science Week, 2005). Prinz’s report includes the research on the discovery of GMR, as it appeared first on 1988. In 1994, the first release and availability upon using GMR (as a magnetic sensor) was commercialized. These first GMR products include the “read” heads (for magnetic hard disk drives) which was released by IBM sometime in November 1997, and had a major economic impact at the time. Followed by the next release of The Honeywell Corporation’s GMR or random access memory or much popularly known as RAM last January 1997, and also gained the next major impact from the population across the globe (Science Week, 2005). The discovery of the concept of the spin polarization among carriers, represent a new direction in the field of electronics (departing from field of magnetic materials or the field of magnetism). Thus, innovation of technology and its advancements enables the demand for the creation of much smaller devices powered by electronics and also enables the capacity to integrate dissimilar materials within a device which serves the purpose of increasing the potential significance of spin-polarization effects (Varadan et. al., 2008). Conclusion The Giant Magneto-resistance or GMR is the ‘quantum mechanical magneto-resistance effect displayed among thin, multi-layered film structures. European researchers have found that there are huge changes which occur on thin-layered materials made of metal as it responds to small magnetic field. Initiated by Peter Grünberg (of Forschungszentrum Jülich (DE), GMR (in trilayers Fe, Cr, Fe) was first discovered. Z.H. Xiong and the other researchers suggest that their study demonstrates spin-polarized carrier injection, detection, and transport which composes spin electronics (spintronics) which can be attained using a pi-conjugated OSE. This includes the authors suggestions of new and different applications in organic spin electronics like spin OLEDs—powered by the useful function of OSEs. Giant Magneto-resistance are sensors with high sensitivity which significantly purports to read heads leading to magnetic fields and that which allows bit size reduction and therefore, increases the magnetic hard disk drive’s storage capacity. Nowadays, modern hard drives are made up of an engineered nanomaterial which contains GMR. On applications, GMRs may be useful for motion sensors or detectors, current transformers, automotive antilock breaks, and the like. List of References Carbone C., & Alvarado, S. F. (1987). Antiparallel coupling between Fe layers separated by a Cr interlayer: Dependence of the magnetization on the film thickness. Physical review, B 36 4): 2433. Grünberg, P., Schreiber, R., Pang, Y, Brodsky, M. B., & Sowers, H. (1986). Layered magnetic structures: Evidence for Antiferromagnetic coupling of Fe layers across Cr interlayers. Physical Review Letters (57) (19):2442-2445. Hinchey, L. L., & Mills, D. L. (1986). Magnetic properties of superlattices formed from ferromagnetic and antiferromagnetic materials. Physical Review: B33, (5): 3329-3343. Science Week (2005). Materials science: On magnetoresistive tunnel junctions. Retrieved on 04 Decmeber 2010 from http://scienceweek.com/2005/sc050107-2.htm Varadan, V.K. et. al., (2008). Nanomedicine: Design and applications of magnetic nanomaterials, nanosensors and nanosystems (pp.123-1234). Chichester, West Sussex, UK: John Wiley & Sons Ltd.   Read More