T. Okuno

Magnetic force microscopy observation of antivortex core with perpendicular magnetization in patterned thin film of permalloy

The cross-tie wall is a kind of magnetic domain wall composed of a main straight wall and crossing subwalls and observed in magnetic thin films. This wall contains two kinds of magnetic vortex structures: “circular vortex” and “antivortex.” At the cores of both vortices, the existence of a spot with perpendicular magnetization has been theoretically predicted. We have detected the perpendicular magnetization spots at each vortex core and identified the direction of it by applying magnetic force microscopy imaging to cross-tie walls in patterned rectangular thin permalloy (Ni80Fe20) films. We also fabricated magnetic structures that contain only antivortex by engineering the shape of thin films.

Propagation of a magnetic domain wall in magnetic wires with asymmetric notches

The propagation of a magnetic domain wall (DW) in a submicron magnetic wire consisting of a magnetic/nonmagnetic/magnetic trilayered structure with asymmetric notches was investigated by utilizing the giant magnetoresistance effect. The propagation direction of a DW was controlled by a pulsed local magnetic field, which nucleates the DW at one of the two ends of the wire. It was found that the depinning field of the DW from the notch depends on the propagation direction of the DW.

Normal mode splitting in interacting arrays of cylindrical permalloy dots

Brillouin light scattering has been exploited to study the dependence of the spin-wave spectrum on the interdot distance in squared arrays of circular permalloy dots with radius R=100nm, thickness L=50nm, and interdot spacing (s) variable in the range between 50 and 800nm. The experimental data have been satisfactorily reproduced using a micromagnetic approach which solves the discretized Landau-Lifshitz-Gilbert equation over a 3×3 matrix of differently spaced circular dots and performing a local Fourier transform. This approach enabled us to clarify that, on reducing the s∕R ratio, some of the normal modes existing within each isolated dot increase their frequency retaining their own character. The fundamental mode, instead, splits into three modes characterized by different profiles of the dynamic magnetization. For all these modes, hybriditazion effects have also been observed.

Magnetization switching of a magnetic wire with trilayer structure using giant magnetoresistance effect

The switching fields of magnetic wires with trilayer structure consisting of NiFe/Cu/Co were investigated using giant magnetic resistance effect. The switching fields of both magnetic layers were observed to be inversely proportional to wire width (150–520 nm). We found that the magnetization of the NiFe layer switches under much lower applied field than in the case of single layer structure by the assistance of the stray field from the magnetic charge of Co at the edge of the wire. Attaching a pad at one end of the wire causes drastic decrease of the switching field. We investigated pad shape dependence of the switching field of the Co layer. For the sample with a square pad we measured the temperature dependence of the switching field between 5 and 300 K. The dependence at low temperatures between 5 and 50 K can be described by the model on thermally assisted magnetization reversal over a simple potential barrier.

Observation of asymmetry in domain wall velocity under transverse magnetic field

The dynamics of a magnetic domain wall (DW) under a transverse magnetic field Hy are investigated in two-dimensional (2D) Co/Ni microstrips, where an interfacial Dzyaloshinskii-Moriya interaction (DMI) exists with DMI vector D lying in +y direction. The DW velocity exhibits asymmetric behavior for ±Hy; that is, the DW velocity becomes faster when Hy is applied antiparallel to D. The key experimental results are reproduced in a 2D micromagnetic simulation, which reveals that the interfacial DMI suppresses the periodic change of the average DW angle φ even above the Walker breakdown and that Hy changes φ, resulting in a velocity asymmetry. This suggests that the 2D DW motion, despite its microscopic complexity, simply depends on the average angle of the DW and thus can be described using a one-dimensional soliton model. These findings provide insight into the magnetic DW dynamics in 2D systems, which are important for emerging spin-orbitronic applications.

Magnetic Properties of Nanoscale Wire and Dot Systems

Magnetic nano-wires and nano-dots were fabricated using an electron-beam lithography and lift-off technique, and the magnetic structures were controlled by engineering the size and shape. We demonstrate here the control of magnetic domain formation and domain wall movement in magnetic nano-wires, the measurement of domain wall resistance using nano-contacts between magnetic nano-wires, and the detection of magnetization reversal of the magnetic vortex core in magnetic nano-dots.

Erratum: Brillouin light scattering investigation of dynamic spin modes confined in cylindrical Permalloy dots [Phys. Rev. B68, 184409 (2003)]

with q2 n = q2 nx + q2 ny + q2 nz and n = 1,2, . . . . After Eq. (4) the symbols qx , qy , and qz should be replaced by qnx , qny , and qnz, respectively. The changes do not affect the numerical calculations presented in Sec. V performed at qnx = 0 for the generic nth backward modes that have a qny component much larger than qnx . The article J. Jorzick, S. O. Demokritov, C. Mathieu, B. Hillebrands, B. Bartenlian, C. Chappert, F. Rousseaux, and A. N. Slavin, Phys. Rev. 60, 15194 (1999) is cited twice, both as Ref. 12 and as Ref. 15.