Magnetic domain-wall dynamics in a submicrometre ferromagnetic structure

Abstract

As fabrication technology pushes the dimensions of ferromagnetic structures into the nanoscale, understanding the magnetization processes of these structures is of fundamental interest, and key to future applications in hard disk drives, magnetic random access memory and other 'spintronic' devices. Measurements on elongated magnetic nanostructures highlighted the importance of nucleation and propagation of a magnetic boundary, or domain wall, between opposing magnetic domains in the magnetization reversal process. Domain-wall propagation in confined structures is of basic interest and critical to the performance of a recently demonstrated magnetic logic scheme for spintronics. A previous study of a 500-nm-wide NiFe structure obtained very low domain-wall mobility in a three-layer device. Here we report room-temperature measurements of the propagation velocity of a domain wall in a single-layer planar Ni80Fe20 ferromagnetic nanowire 200 nm wide. The wall velocities are extremely high and, importantly, the intrinsic wall mobility is close to that in continuous films, indicating that lateral confinement does not significantly affect the gyromagnetic spin damping parameter to the extreme extent previously suggested. Consequently the prospects for high-speed domain-wall motion in future nanoscale spintronic devices are excellent.

Surface Morphology and Magnetic Properties of Isolated Cylindrical Nickel Nanowires

“…In this system, the laser spot was focused to a diameter of approximately 5 µm. The change in the polarisation angle of the laser light after reflection from the sample was proportional to the longitudinal component of the wire magnetisation [5,7,32,50]. The reflected light passed through an analysing prism and the intensity detected using a silicon photodiode connected to a high-bandwidth amplifier and a ~1 GHzbandwidth oscilloscope.…”

“…Thus, this setup was used for hysteresis loop measurements of a collection of closely packed two Ni nanowires. More information about MOKE setup can be found in Refs [5,7,32,50]. Figure 1 show high resolution scanning electron microscopy micrograph examples of single cylindrical Ni nanowires with different diameters, lengths and surface morphologies lying on the gold premarked silicon substrates following release and deposition from the same dilute suspension.…”

“…Magneto-Optical Kerr Effect (MOKE) magnetometry has been widely used to study the magnetisation behaviour of two dimensional arrays of ferromagnetic nano and micro dots [10], stripes and planar nanowires [1,7] fabricated by conventional electron beam lithography and lift-off techniques. In MOKE setup, however, the measured output of Kerr signal is proportional to the amount of magnetisation that depends upon the polarisation rotation of a linearly polarised laser light following its reflection from a magnetic surface [1,7,10,32,45,5].…”

“…In MOKE setup, however, the measured output of Kerr signal is proportional to the amount of magnetisation that depends upon the polarisation rotation of a linearly polarised laser light following its reflection from a magnetic surface [1,7,10,32,45,5]. Such MOKE measurements are potentially interesting, as it provides a very sensitive probe that is proportional to the change in the surface magnetisation to a depth of the order of skin-depth of the material [32].…”

Current-driven magnetic domain wall motion and its real-time detection

“…To achieve controlled magnetic DW motion, magnetic-fieldbased control was investigated in the early stage of research. [1][2][3][4] However, a magnetic field is not able to drive multiple DWs along the same direction and thus, is hardly applicable to DW-motion-based memory devices. In 1996, Berger showed in his seminar paper that an electric current can move multiple DWs along the same direction.…”