IOP PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 43 (2010) 264005 (10pp) doi:10.1088/0022-3727/43/26/264005 Magnonic logic circuits Alexander Khitun, Mingqiang Bao and Kang L Wang Device Research Laboratory, Electrical Engineering Department, Focus Center on Functional Engineered Nano Architectonics (FENA), Western Institute of Nanoelectronics (WIN), University of California at Los Angeles, Los Angeles, California, 90095-1594, USA Received 23 November 2009, in final form 31 March 2010 Published 17 June 2010 Online at stacks.iop.org/JPhysD/43/264005 Abstract We describe and analyse possible approaches to magnonic logic circuits and basic elements required for circuit construction. A distinctive feature of the magnonic circuitry is that information is transmitted by spin waves propagating in the magnetic waveguides without the use of electric current. The latter makes it possible to exploit spin wave phenomena for more efficient data transfer and enhanced logic functionality. We describe possible schemes for general computing and special task data processing. The functional throughput of the magnonic logic gates is estimated and compared with the conventional transistor-based approach. Magnonic logic circuits allow scaling down to the deep submicrometre range and THz frequency operation. The scaling is in favour of the magnonic circuits offering a significant functional advantage over the traditional approach. The disadvantages and problems of the spin wave devices are also discussed. 1. Introduction There is an immense practical need for novel logic devices capable of overcoming the constraints inherent to conventional transistor-based logic circuitry [1]. After decades of miniaturization, there is still plenty of room for scaling down the size of the metal-oxide-semiconductor field effect transistor (MOSFET) and for increasing the device density in the complementary metal-oxide-semiconductor (CMOS) logic circuits. However, it is widely believed that further MOSFET shrinkage will be inefficient due to the power dissipation problem. Besides that, the growing number of devices per unit area results in tremendous difficulties with interconnection wiring [2]. Impedance match between devices and wires is another serious issue. A radical solution to the above- mentioned problems would be the development of transistor- less logic circuits implementing more efficient mechanisms for information transmission and processing. In this work, we consider magnonic logic circuits as one of the possible routes. Spin wave (magnons) as a physical phenomenon has attracted scientific interest for a long time [3]. Spin wave propagation has been studied in a variety of magnetic materials and nanostructures [4–6]. Relatively slow group velocity (more than two orders of magnitude slower than the speed of light) and high attenuation (more than six orders of magnitude higher attenuation than for photons in a standard optical fibre) are two well-known disadvantages, which explain the lack of interest in spin waves as a potential candidate for information transmission. The situation has changed drastically as the characteristic distance between the devices on the chip entered the deep-submicrometre range. It has become more important to have fast signal conversion/modulation, while the short travelling distance compensates slow propagation and high attenuation. From this point of view, spin waves possess certain technological advantages: (i) spin waves can be guided in the magnetic waveguides similar to the optical fibres; (ii) spin wave signal can be converted into a voltage via inductive coupling; (iii) magnetic field can be used as an external parameter for spin wave signal modulation. The wavelength of the exchange spin waves can be as short as several nanometres, and the coherence length may exceed tens of micrometres at room temperature. The latter translates into the intriguing possibility of building scalable logic devices utilizing spin wave inherent properties. The first working spin-wave based logic device has been experimentally demonstrated by Kostylev et al [7]. The authors used the Mach–Zehnder-type current-controlled spin wave interferometer to demonstrate output voltage modulation as a result of spin wave interference. This first working prototype device was of considerable importance for the development of magnonic logic devices. The device operates in the GHz frequency range and at room temperature. This immediately made it a favourite among the other proposed spin-based logic devices. Later on, exclusive-not-OR and 0022-3727/10/264005+10$30.00 1 © 2010 IOP Publishing Ltd Printed in the UK & the USA