INTRODUCTION TO
SPINTRONICS
Josh Schaefferkoetter
INTRODUCTION
Conventional electronic devices ignore the spin property and rely strictly on the transport of the electrical charge of electrons
FUTURE DEMANDS
Moore’s Law states that the number of transistors on a silicon chip will roughly double every eighteen months By 2008, it is projected that the width of the electrodes in a microprocessor will be 45nm across
As electronic devices become smaller, quantum properties of the wavelike nature of electrons are no longer
negligible
Spintronic devices offer the possibility of enhanced functionality, higher speed, and reduced power
ADVANTAGES OF SPIN
Information is stored into spin as one of two possible orientations
Spin lifetime is relatively long, on the order of nanoseconds
Spin currents can be manipulated
Spin devices may combine logic and storage functionality eliminating the need for separate components
Magnetic storage is nonvolatile
GMR
1988 France, GMR discovery is accepted as birth of spintronics
A Giant MagnetoResistive device is made of at least two ferromagnetic layers separated by a spacer layer When the magnetization of the two outside layers is aligned, lowest resistance
Conversely when magnetization vectors are antiparallel, high R
PARALLEL CURRENT GMR
Current runs parallel between the ferromagnetic layers Most commonly used in magnetic read heads
SPIN VALVE
Simplest and most successful spintronic device
PERPENDICULAR CURRENT GMR
Easier to understand theoretically, think of one FM layer as spin polarizer and other as detector
Has shown 70% resistance difference between zero point and antiparallel states
TUNNEL MAGNETORESISTANCE
Tunnel Magnetoresistive effect combines the two spin channels in the ferromagnetic materials and the quantum tunnel effect
MRAM
MRAM uses magnetic storage elements instead of electric used in conventional RAM
MRAM
Attempts were made to control bit writing by using relatively large currents to produce fields
SPIN TRANSFER
Current passed through a magnetic field becomes spin polarized
This flipping of magnetic spins applies a relatively large torque to the magnetization within the external magnet This torque will pump energy to the magnet causing its magnetic moment to precess
If damping force is too small, the current spin
momentum will transfer to the nanomagnet, causing the magnetization will flip
Unwanted effect in spin valves
MRAM
The spin transfer mechanism can be used to write to the magnetic memory cells
MRAM
MRAM promises:
⚫ Density of DRAM
⚫ Speed of SRAM
SPIN TRANSISTOR
Ideal use of MRAM would utilize control of the spin channels of the current
Spin transistors would allow control of the spin current in the same manner that conventional transistors can switch charge currents
Using arrays of these spin transistors, MRAM will combine storage, detection, logic and communication capabilities on a single chip
DATTA DAS SPIN TRANSISTOR
The Datta Das Spin Transistor was first spin device proposed for metal-oxide geometry,
1989
Emitter and collector are ferromagnetic with parallel magnetizations
The gate provides magnetic field
Current is modulated by the degree of precession in
MAGNETIC SEMICONDUCTORS
Materials like magnetite are magnetic semiconductors Development of materials similar to conventional
Research aimed at dilute magnetic semiconductors
⚫ Manganese is commonly doped onto substrate
⚫ However previous manganese-doped GaAs has transition temp at
-88oC
MAGNETIC SEMICONDUCTORS
F. Matsukura, H. Ohno, A. Shen, and Y. Sugawara, “Transport Properties and Origin of Ferromagnetism in (Ga,Mn)As,” Phys. Rev. B57, R2037 (1998).
A. M. Nazmul, T. Amemiya, Y. Shuto, S. Sugahara, and M. Tanaka, “High Temperature Ferromagnetism in GaAs-Based Heterostructures with Mn Delta Doping”; see http://arxiv.org/cond-mat/0503444 (2005). F. Matsukura, E. Abe, and H. Ohno, “Magnetotransport Properties of (Ga, Mn)Sb,” J. Appl. Phys.87, 6442 (2000).
X. Chen, M. Na, M. Cheon, S. Wang, H. Luo, B. D. McCombe, X. Liu, Y. Sasaki, T. Wojtowicz, J. K. Furdyna, S. J. Potashnik, and P. Schiffer, “Above-Room-Temperature Ferromagnetism in GaSb/Mn Digital Alloys,” Appl. Phys. Lett.81, 511 (2002). Y. D. Park, A. T. Hanbicki, S. C. Erwin, C. S. Hellberg, J. M. Sullivan, J. E. Mattson, T. F. Ambrose, A. Wilson, G. Spanos, and B. T. Jonker, “A Group-IV Ferromagnetic Semiconductor: MnxGe1−x,” Science295, 651 (2002).
Y. Matsumoto, M. Murakami, T. Shono, T. Hasegawa, T. Fukumura, M. Kawasaki, P. Ahmet, T. Chikyow, S. Koshihara, and H. Koinuma, “Room-Temperature Ferromagnetism in Transport Transition Metal-Doped Titanium Dioxide,” Science291, 854 (2001).
M. L. Reed, N. A. El-Masry, H. H. Stadelmaier, M. E. Ritums, N. J. Reed, C. A. Parker, J. C. Roberts, and S. M. Bedair, “Room Temperature Ferromagnetic Properties of (Ga, Mn)N,” Appl. Phys. Lett.79, 3473 (2001).
S. Cho, S. Choi, G.-B. Cha, S. Hong, Y. Kim, Y.-J. Zhao, A. J. Freeman, J. B. Ketterson, B. Kim, Y. Kim, and B.-C. Choi, “Room-Temperature Ferromagnetism in (Zn1−xMnx)GeP2 Semiconductors,” Phys. Rev. Lett.88, 257203 (2002).
S. B. Ogale, R. J. Choudhary, J. P. Buban, S. E. Lofland, S. R. Shinde, S. N. Kale, V. N. Kulkarni, J. Higgins, C. Lanci, J. R. Simpson, N. D. Browning, S. Das Sarma, H. D. Drew, R. L. Greene, and T. Venkatesan, “High Temperature Ferromagnetism with a Giant Magnetic Moment in Transparent Co-Doped SnO2−δ,” Phys. Rev. Lett.91, 077205 (2003).
Y. G. Zhao, S. R. Shinde, S. B. Ogale, J. Higgins, R. Choudhary, V. N. Kulkarni, R. L. Greene, T. Venkatesan, S. E. Lofland, C. Lanci, J. P. Buban, N. D. Browning, S. Das Sarma, and A. J. Millis, “Co-Doped La0.5Sr0.5TiO3−δ: Diluted Magnetic Oxide
System with High Curie Temperature,” Appl. Phys. Lett.83, 2199–2201 (2003).
H. Saito, V. Zayets, S. Yamagata, and K. Ando, “Room-Temperature Ferromagnetism in a II–VI Diluted Magnetic Semiconductor Zn1−xCrxTe,” Phys. Rev. Lett.90, 207202 (2003).
P. Sharma, A. Gupta, K. V. Rao, F. J. Owens, R. Sharma, R. Ahuja, J. M. Osorio Guillen, B. Johansson, and G. A. Gehring, “Ferromagnetism Above Room Temperature in Bulk and Transparent Thin Films of Mn-Doped ZnO,” Nature Mater.2, 673 (2003). J. Philip, N. Theodoropoulou, G. Berera, J. S. Moodera, and B. Satpati, “High-Temperature Ferromagnetism in Manganese-Doped Indium–Tin Oxide Films,” Appl. Phys. Lett.85, 777 (2004).
H. X. Liu, S. Y. Wu, R. K. Singh, L. Gu, D. J. Smith, N. R. Dilley, L. Montes, M. B. Simmonds, and N. Newman, “Observation of Ferromagnetism at over 900 K in Cr-doped GaN and AlN,” Appl. Phys. Lett.85, 4076 (2004).
S. Y. Wu, H. X. Liu, L. Gu, R. K. Singh, M. van Schilfgaarde, D. J. Smith, N. R. Dilley, L. Montes, M. B. Simmonds, and N. Newman, “Synthesis and Characterization of High Quality Ferromagnetic Cr-Doped GaN and AlN Thin Films with Curie Temperatures Above 900 K” (2003 Fall Materials Research Society Symposium Proceedings), Mater. Sci. Forum798, B10.57.1 (2004).
CURRENT RESEARCH
Weitering et al. have made numerous advances
⚫ Ferromagnetic transition temperature in excess of 100 K in
(Ga,Mn)As diluted magnetic semiconductors (DMS's).
⚫ Spin injection from ferromagnetic to non-magnetic
semiconductors and long spin-coherence times in semiconductors.
⚫ Ferromagnetism in Mn doped group IV semiconductors.
⚫ Room temperature ferromagnetism in (Ga,Mn)N, (Ga,Mn)P,
and digital-doped (Ga,Mn)Sb.
⚫ Large magnetoresistance in ferromagnetic semiconductor tunnel
CURRENT RESEARCH
Material science
⚫ Many methods of magnetic
doping
CONCLUSION
Interest in spintronics arises, in part, from the looming problem of exhausting the fundamental physical limits of conventional
electronics.
However, complete reconstruction of industry is unlikely and spintronics is a “variation” of current technology
The spin of the electron has attracted renewed interest because it promises a wide variety of new devices that combine logic, storage and sensor applications.
Moreover, these "spintronic" devices might lead to quantum computers and quantum communication based on electronic
