Magnetic Domain Wall Dynamics Muhammad Shahbaz Anwar Leiden
Magnetic Domain Wall Dynamics Muhammad Shahbaz Anwar Leiden University
Magnetic domain and Domain Wall (DW) In 1907, Weiss gave an idea about the magnetic domains, regions inside the material, which are fully magnetized in particular direction but in different with each other so that the net magnetization is zero. Domain walls separate one domain from another. Block Wall Neel Wall Cross Tie wall Weiss, J. Phys. 6, 401 (1907). Closure domain wall
Magnetic domain wall motion Required magnetic field Hr>Hc Magnetic domain wall motion in Permalloy thin films by applied a magnetic field Parkin et al. Science 320, 190 (2008). Required magnetic field Jr>Jc Domain Wall movement in Permalloy nano wires
Application: Racetrack Memories (RM) • DW velocity determines the speed of RM HDD • DW motion requires high current density resulting in Joule heating • Effect of stray magnetic field Parkin et al. Science 320, 190 (2008). Solid State RAM
DW motion in theory There are two different theoretical approaches to explain the DW motion, Ballistic limit Spin transfer torque effect, DW velocity, critical current density increases not only with spin polarization but also with reduced wall width. Diffusive limit Spin of charge carriers follows the local magnetization that introduced adiabatic torque into Landau Lifshitz-Gilbert equation. Conflict between experimental and theoretical investigations introduced a nonadiabatic term. In diffusive regime, adiabatic and nonadiabatic terms depend on equivalent velocity (u) u = JPgu. B/2 e. Ms P = spin polarization, J = critical current density Ms = saturation magnetization For Half Metallic ferromagnet Cr. O 2 (Tc=393 K) the P=100%, Ms=4. 75 105 A/m, that resulting in value of u more than four timer higher than that of Permalloy. Gopar, et al. Phys. Rev. B 69, 014426 (2004). Tatara et al. Phys. Rev. Lett. 92, 086601 (2004). Li, et al. Phys. Rev. Lett. 92, 207203 (2004).
Domain wall motion in Half Metallic Cr. O 2 AFM micrograph of Cr. O 2/Ti. O 2 Li, et al. Appl. Phys. Lett. 75, 713 (1999). Biehler, et al. Phys. Rev. B. 75, 184427 (2007). Influence of current on DW in Cr. O 2 along easy and hard direction along with micromagnetic simulation
Cr. O 2 is the best material to study the DW dynamics Thanks
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