Domain Wall Memory Device

Magnetic domain walls in confined geometries have attracted much interest in the last couple of years for a number of reasons. On the one hand, new physical phenomena such as current-induced domain wall motion due to the highly debated nonadiabatic spin torque and novel spin–orbit torques have been investigated. On the other hand, the proposal of the racetrack memory concept as a universal data storage device has stimulated much research. In such a device, domain walls in magnetic nanowires are used as bits of information which can be shifted, e.g., to locate them at the position of a read head, without the need to move physically any material. The prospect of memory and logic devices has spurred an intense research, in particular into different materials with promising properties for domain walls and domain wall motion. The critical parameters to be optimized are mainly domain wall lateral sizes, directly governing the possible information density, and domain wall movement and pinning/depinning processes that determine access time and energy consumption. The ability to control and manipulate domain walls precisely opens up avenues to designing a range of novel and highly competitive devices. In this chapter, a review of the properties of magnetic domain walls in nanowires and the possibilities to control and manipulate them is given. Precise control and efficient manipulation of domain walls is the prerequisite for any device. Different material classes and the resulting domain wall types are reviewed. The basic operations that are necessary for a device, i.e., nucleation, displacement, and detection of domain walls, are discussed for these material classes. Examples of devices using magnetic domain walls are briefly reviewed, including memory and logic applications. The first commercial nonvolatile multiturn sensor product that is based on magnetic domain walls and combines sensing and memory is described in more detail. List of Abbreviations 1D, 2D, 3D One, two, or three dimensional 3d Elements from the first side group in the periodic table with 3D electron in the outer shell, from Sc to Zn, in magnetic context usually Fe, Co, Ni (Mn, Cr), and their alloys AMR Anisotropic magnetoresistance ccw Counterclockwise CFAS Co2FeAl0.4Si0.6 CIDWM Current-induced domain wall motion CIP Current in-plane CMOS Complementary metal oxide semiconductor CPP Current perpendicular to plane cw Clockwise *Email: mfoerster@cells.es Handbook of Spintronics DOI 10.1007/978-94-007-7604-3_48-1 # Springer Science+Business Media Dordrecht 2015