Kunihiro Nakano

Current-Driven Domain Wall Motion in CoCrPt Wires with Perpendicular Magnetic Anisotropy

We report the direct observation of current-driven domain wall (DW) motion in a CoCrPt wire with perpendicular magnetic anisotropy. Magnetic force microscopy showed that a single DW introduced in the wire is displaced back and forth by positive and negative pulsed current. This is the first demonstration of the current-driven DW motion in a metallic magnetic wire with perpendicular magnetic anisotropy in the absence of a magnetic field.

All-electrical operation of magnetic vortex core memory cell

A single vortex-core switching in a ferromagnetic disk is detected in real time by using a three-terminal device with the tunneling magnetoresistance junction. We show that the device works as a vortex core memory cell, where reading and writing can be done in an all-electrical way: binary data corresponding to the core direction can be read out electrically as the amplitude of the output, while the data can be written electrically by applying a pulsed current.

Three-Terminal Device Based on the Current-Induced Magnetic Vortex Dynamics with the Magnetic Tunnel Junction

Current-induced resonant motion of the vortex core was probed by a three-terminal device with the magnetic tunnel junction. The large output signal due to the large magnetoresistance ratio of the magnetic tunnel junction allows us to detect the vortex dynamics clearly. The output signal can be tuned by the dc bias voltage, indicating that the device acts as a resonant transistor.

Magnetization Configurations in NiFe Slotted Rings Studied by Magneto-Optical Kerr Effect and Magnetic Force Microscopy

The magnetization states and the reversal mechanisms of 30 nm thick NiFe full and slotted rings, with outer and inner diameter of 1400 nm and 600 nm, respectively, are analysed by magneto-optical Kerr effect and in-field magnetic force microscopy. The evolution of the magnetization configuration is investigated as a function of the applied field intensity. Both the measured hysteresis loops and the MFM images are satisfactorily reproduced by a combined micromagnetic and analytical approach, showing that the presence of the slot in one arm of the ring forces the system to undergo a transition into a flux closure vortex state of well defined chirality. Both the reversal mechanism and the field range where the vortex exists are influenced by the aperture angle of the slot.

Real-time observation of electrical vortex core switching

A single vortex-core switching induced by current injection into a ferromagnetic disk is detected in real time using a three-terminal device with the tunneling magnetoresistance junction. The real time observation reveals that the electrical core switching is completed within a few 100 ps. It is also found that the core switching takes place at the specific positions inside the disk.

Electrical Detection of Vortex Core Polarity in Ferromagnetic Disk

The current-induced dynamics of a vortex core in a ferromagnetic disk was investigated by using a three-terminal device with the magnetic tunnel junction (MTJ). The gyroscopic motion of a core was detected as the periodic oscillation of the output signal from the MTJ. It was found that the amplitude of the output signal is determined by the core polarity, which can be used for electrical reading of the bit information of the vortex core memory cell.