Indian Journal of Pure & Applied Ph ys ics V ol. 40, November 2002, pp. 835-836

News Scan The emerging technology of types of calcu lat ions . In quantum mechanics, an can be in both -up and spin -down spintronics states, at the same time. The mixed state coul d form Every appliance from electri c bulb to laptop th e base of a , built around not binary bits computer works on the principl e of transport of but the qu antum bits or qubit. It is any combinati on electri cal charge carri ers-, whi ch cause of a I or a O. The simpl est device usin g spin­ dependent effect is a sand wich with two macrnetic electri c current to fl ow through wires. The electrons b have both charge and spin . The spin of th e electrons layers surrounding a non-magnetic metal or could greatly enhance th e p;1rticles' usefulness . The in su lator. If the two magneti c layers are different , se mi conductor techn ology is based on th e number th en th e magneti zation direction of one can be of charges and th eir energy . The electroni c dev ices rotated with respect to the other. This leads to the such as wo rk due to fl ow of charge. The utili za ti on of these structures as sensor elements and cr for memory elements. Ph ys icists are now tryin g to electron can be ass umed as tin y rotatin b bar macrb net with two possibl e ori entations : spin- up or spin- use the property of th e electron-like spin rath er than charge to develop new generati on of mi croelectro ni c down. An appli ed magnetic fi eld can flip e l ec tron ~~ from one state to anot her. rn thi s way, sp in can be dev ices whi ch may be more ve rsati Ie and robust measured and manipulated to represent the O's and th an sili con chips and circuit elements. Spin s appear l's of digit al programming, analogous to the to be remarkably robust and move relati ve ly easi ly between semi conductors. rn case of electron "current 0 11 and current off' states in a conventi onal sili con chip. The stud y of electron spin in material s transport from one material to another, the spins do is ca ll ed Spi ntroni cs. Spintroni cs is based on the not lo se its orientati on or scatter from impurities or direction of spin and sp in-coupling (Na /ure, Ap ril , structural effects [Cho A, Science, 296 (2002) 246]. 2002) A computer's main components are random A revoluti onary new class of semiconductor access memory (RAM) for programming, a hard electronics based on the spin degree of freedom di sk for storage of information and a central processin g unit (CPU) for perfonnin cr computin cr could be created. The performance of conve nti onal b b devices is limited in speed and dissipati on whereas operations. The CPU and RAM are semi conductor- spintronics dev ices are capable of much hi gher based whil e, th e hard di sk stores information speed at very low power. Spintroni cs tran sistors magneti call y. The advantage of spintronics over may work at a faster speed, are also small er in size electronics is th at, the magnets tend to stay and wi II consume less power. Spins can be oriented ma gneti zed. A computer with all -magnetic RAM in one direction or th e oth er, ca ll ed spin-up or spin­ wo uld always reta in the information put int o it. down . When electrons' sp in s are ali gned in one When th e power is first turned on, there wo ul d be direction, these create a net magneti c moment as no "boot up " wa iting period. This would be a quite seen in magnetic materi als like, iron and cobalt. usefu l property for laptop . The re­ Magnetism IS an in tri n!-.ic ph ys ical propert y programmable magneti c processors ancl unlimited associated with the sp in s of eiectron s in a material. RAM, combined with hi gh density and heat­ The electron spin Illay exist not on ly in the up or dissipati ng ab ility of magnetic materia ls w0uld down state but al so In infinitely many Intermediate k t'initely be of much use. The ferromagnetic l

spintronic sandwiches has been built. Magnetized solar radiation, The solar radiation routinely disrupts patches on the spinning hard disk flips th e spi n-state satellites when there are solar storms. Another use is in the read-head, back and forth, transmitting digital in military where, the computers can withstand the data. A spintronic read-head can detect much pulse of e lectromagnetic radiation sent out by a weaker magnetic fields than older devices. It is the nuclear blast. The microelectronic devices that most sensiti ve detector of magnetic fields at room function by using the spin of the e lectron may lead temperature. Due to spintronics, the hard drives to the development of quantum microchips could hold up to 100 gigabytes or more compared to (Scielltific American, June, 2002). less than I gigabyte, five years ago. Stuart Parkin of A ll spintronics devices work according to Almaden along with researchers at Honeywell , simple principle: information is stored in to the spins Motorola and the Naval Research Laboratory are as a particular spin orientation (up or down); the trying to create spi n-based computer memory spins being attached to mobi le electrons, carry the called, magnetic random access memory or M­ information along the wire and the information is RAM. A prototype design contains a series of tiny read at the terminal. Two recent discoveri es: ( I) magnetic sandwic hes, placed on a chip opticall y induced long-lived coherent spin-State in between c ri ss-crossing arrays of wires. The e lectri c semiconductors and (2) in current through the wires flips the spin. M-RAM semiconducting GaMnAs will lead to revolutionary could make it possible to build longer-lived advances in 21 st century photonics and e lectronics spacecraft that performs more functions without such as, very high performance opto-electronic requiring additional power. M-RAM might lead to devices, very fast, very dense memory and logic at build computers and cell phones with so muc h built­ extremely low power, spin quantum devices like in me mory that, they could store an entire Spin-Fets, Spin LEOs and Spin RTDs and quantum conversation. A magnetic chip could use much less in conventional semiconducto rs at room power than conventional electronics and is ideal for temperature etc (Wolf S A et al., Science, 294 mobile communication and laptop computers. The (200 I) 1488. The emerging tec hnology of magnetic chips can be made out of just a few layers spintronics may soon make it possib le to store of metals and would be hard, easier and cheaper to movies on a PalmPi lot or build a new computer. make than current e lectronic circuits. The magnetic chips could be used in space, where these would Poonam Bhatt replace e lectronics, which require protection from