Dynamic response of the vortex magnetization in multilayered magnetic nanopillars to the spin-polarized current pulse has been investigated numerically. The equilibrium magnetization configurations in both magnetic layers are the vortex states with single magnetization cores at the disk center. It was found that the chirality of the vortex state in magnetic free layer can be controllably switched by applying current pulse with appropriate amplitude, polarity, and duration. The critical current density required for the chirality switching is found to be on the order of 108A∕cm2.

We investigated the influence of the magnetic field pulse parameters and the size of the Fe element to the vortex core switching by micromagnetic modeling. When the magnetic field pulse with an appropriate strength and duration is applied to 30nm thick Fe circular disks with diameters between 100nm and 1μm, the vortex configuration is perturbed away from the equilibrium state, and the circular symmetric distribution of the in-plane magnetization around the vortex core deforms. This leads to the creation of a new vortex core with the opposite polarity and an antivortex. With increasing time, the vortex-antivortex pair annihilates. As a result of the annihilation, a single vortex core with opposite polarity remains and a vortex core switch is realized. The process of core switching, however, strongly depends on the amplitude and duration of the magnetic pulse.

A series of Fe-Co alloys were produced at the atomic scale, onto 15 nm Cu buffer layers, using pulsed-current deposition. The relationship between saturation magnetization, Ms and lattice constant, a has been investigated. The effects of increasing stacking number (bilayer number) on the values of Ms and a have been examined. The alloys showed a maximum room temperature Ms of 240 emu/g at 25 at. % Co. A study to the room temperature magnetic and microstructure analysis revealed that the increase in saturation magnetization strongly correlates with the lattice constant of the Fe-Co alloy.

We report on the development of a new magnetic microscope, time-resolved near-field scanning magneto-optical microscope, which combines a near-field scanning optical microscope and magneto-optical contrast. By taking advantage of the high temporal resolution of time-resolved Kerr microscope and the sub-wavelength spatial resolution of a near-field microscope, we achieved a temporal resolution of ∼50 ps and a spatial resolution of <100 nm. In order to demonstrate the spatiotemporal magnetic imaging capability of this microscope, the magnetic field pulse induced gyrotropic vortex dynamics occurring in 1 μm diameter, 20 nm thick CoFeB circular disks has been investigated. The microscope provides sub-wavelength resolution magnetic images of the gyrotropic motion of the vortex core at a resonance frequency of ∼240 MHz.

The vortex-driven magnetization process of micron-sized, exchange-coupled square elements with composition of Ni 80 Fe 20 (12 nm)/Ir 20 Mn 80 (5 nm) is investigated. The exchange-bias is introduced by field-cooling through the blocking temperature (T B ) of the system, whereby Landau-shaped vortex states of the Ni 80 Fe 20 layer are imprinted into the Ir 20 Mn 80 . In the case of zero-field cooling, the exchange-coupling at the ferromagnetic/antiferromagnetic interface significantly enhances the vortex stability by increasing the nucleation and annihilation fields, while reducing coercivity and remanence. For the field-cooled elements, the hysteresis loops are shifted along the cooling field axis. The loop shift is attributed to the imprinting of displaced vortex state of Ni 80 Fe 20 into Ir 20 Mn 80 , which leads to asymmetric effective local pinning fields at the interface. The asymmetry of the hysteresis loop and the strength of the exchange-bias field can be tuned by varying the strength of cooling field. Micromagnetic modeling reproduces the experimentally observed vortex-driven magnetization process if the local pinning fields induced by exchange-coupling of the ferromagnetic and antiferromagnetic layers are taken into account.