S. A. Haque

Systematic investigation of Permalloy nanostructures for magnetologic applications

Magnetic logic gates based on magnetostatically coupled ferromagnetic structures show a great promise for future information processing. The absolute size and shape of the elementary structures determine their intrinsic and interaction properties and thus have to be chosen appropriately in order to allow for binary logic operations. Here, we present a systematic study of the switching behavior, stray field, and coupling of Permalloy nanostructures as a function of geometrical parameters using micromagnetic simulations. We show that bow-tie shaped elements are promising for magnetic logic gates.

Threshold thickness and magnetic properties of a composite Ni/GaAs (001)

The magnetization process and the coercivity of Ni films in the thickness range of 15–70 nm deposited onto GaAs (001) substrate are studied. The coercivity of the Ni film having thicknesses larger than a threshold value is observed to be high. The magnetization processes of the Ni film having high coercivity differs from that of the film having low coercivity but in each phase it is observed to be identical. The anisotropy is calculated using the magnetization. In order to discuss the microscopic origin of the anomalous properties in the magnetization, the experimental results are reviewed by introducing a uniaxial anisotropy, which is calculated from the easy-axis and hard-axis magnetization. The calculated anisotropy is able to explain the temperature and angle dependency of the FMR spectra of the Ni film. The surface roughness is also explored in connection to the anomaly.

High field magnetoresistance and ESR measurements on Ni stripes on GaAs substrate

Ni nanowires fabricated on a GaAs substrate, which have width narrower than 500 nm and thickness 50 nm, showed an antiferromagnetic-like domain structure. Many Ni nanowires fabricated on GaAs using the electron beam lithography technique have been studied by electron spin resonance (ESR). Splitting of ESR signals in the frequency-field diagram was observed around 57 GHz, although only a ferromagnetic resonance mode was observed for other frequencies. This mode is suggested to be an antiferromagnetic resonance related to the domain structure on the Ni nanowires.

Perpendicular Magnetic Anisotropy in Thin Ni Films on GaAs (001)

Polycrystalline thin Ni films deposited onto GaAs (001) show a transition of the magnetic anisotropy depending on its thickness. The anisotropy is perpendicular to the film plane for the thicknesses of the film equal to or less than 12 nm. This becomes in-plane in the films having thicknesses equal to or higher than 15 nm. The films are deposited onto the n-type GaAs (001) substrate by the electron beam evaporation in ultra high vacuum (UHV) in the standard molecular beam epitaxy (MBE) system. The experimental results are reviewed by introducing a uniaxial anisotropy, which is calculated from the easy-axis and hard-axis magnetization obtained by the superconducting interference device (SQUID) at various temperatures.