Zengtai Zhu

Top-down control of dynamic anisotropy in permalloy thin films with stripe domains

Permalloy films with different thickness were prepared for comparison, and the dynamic properties of the stripe domains were investigated by using a vector network analyzer ferromagnetic resonance (VNA-FMR) technique. A top-down approach was used to control the thickness of the films. In the measurement of permeability spectra, an applied magnetic field H app was employed parallel and perpendicular to the stripe domains, respectively. Dynamic pseudo-uniaxial anisotropy fields are derived. In order to explain the anisotropy variation of permalloy films, a theoretical model has been proposed, and the result shows that the pseudo-uniaxial anisotropy can be attributed to the contributions of saturation magnetization, exchange interaction, perpendicular anisotropy, and film thickness. In addition, with the increase of H app, the stripe domains gradually rotate towards the direction of the applied field, which can be clearly observed by magnetic force microscopy. Moreover, the dynamic permeability spectra exhibit a rhythmic variation dependent on the rotation of the stripe domains, i.e. the relationship between the rotational stripe domains and resonance frequency.

Annealing influence on the exchange stiffness constant of Permalloy films with stripe domains

An investigation of the annealing influence on the stripe domains structure in Permalloy films has been performed by comparing the static and dynamic magnetic properties. An increasing exchange stiffness constant A ex is found when the annealing temperature rises. The magnetic force microscopy images show that the width of stripe domain increases with the increase of annealing temperature, and the increasing exchange stiffness constant is considered to be the most prominent reason. A perpendicular standing spin-wave model is used to deduce the A ex from the evolution of resonance frequencies, and the A ex increases nearly twice from 7.2 × 10−7 ergs cm−1 for the as-deposited film to 12.9 × 10−7 ergs cm−1 for the film annealing at 400 °C. Micromagnetic calculation is also used to compute the magnetization configuration, and the results agree well with the experimental conclusions.

A short-circuited coplanar waveguide to measure the permeability of magnetic thin films: Comparison with short-circuited microstrip line

A short-circuited coplanar waveguide jig is proposed for complex permeability measurements in soft magnetic FeNi thin films. Measurements using a short-circuited microstrip line are also performed for comparison and analyzed using the Landau-Lifshitz-Gilbert equation.

Tuning high frequency magnetic properties and damping of FeGa, FeGaN and FeGaB thin films

A series of FeGa, FeGaN and FeGaB films with varied oblique angles were deposited by sputtering method on silicon substrates, respectively. The microstructure, soft magnetism, microwave properties, and damping factor for the films were investigated. The FeGa films showed a poor high frequency magnetic property due to the large stress itself. The grain size of FeGa films was reduced by the additional N element, while the structure of FeGa films was changed from the polycrystalline to amorphous phase by the involved B element. As a result, N content can effectively improve the magnetic softness of FeGa film, but their high frequency magnetic properties were still poor both when the N2/Ar flow rate ratio is 2% and 5% during the deposition. The additional B content significantly led to the excellent magnetic softness and the self-biased ferromagnetic resonance frequency of 1.83 GHz for FeGaB film. The dampings of FeGa films were adjusted by the additional N and B contents from 0.218 to 0.139 and 0.023, respec...