Nguyen Duy Ha

Novel nanostructure and magnetic properties of Co–Fe–Hf–O films

The influence of the partial pressure of oxygen (PO2) on the microstructural and magnetic properties of sputtered Co?Fe?Hf?O films has been studied. It is shown that the films prepared under PO2 = 6?11.5% with large saturation magnetization, 4?Ms~18?21?kG, large hard-axis anisotropy field, HkH~30?84?Oe, and high electrical resistivity, ?~1400?3600????cm, are excellent candidate materials for high-frequency applications of micromagnetic devices such as magnetic thin film inductors, transformers and thin film flux gate sensors. In particular, the good soft magnetic properties of Co19.35Fe53.28Hf7.92O19.35 nanocomposite films of 50?437?nm thickness, in addition to their high electrical resistivity, make them ideal for use in micromagnetic devices with an opening bandwidth of several gigahertz. This is attributed to the formation of a peculiar nanostructure in these samples. A strong magnetic phase separation appears to occur as the film thickness increases over 437?nm, which, in turn, modifies the high-frequency magnetic behaviour of the Co19.35Fe53.28Hf7.92O19.35 film.

Thickness dependence of parallel and perpendicular anisotropic resistivity in Ta/NiFe/IrMn/Ta multilayer studied by anisotropic magnetoresistance and planar Hall effect

Ferromagnetic layer thickness dependence of anisotropic magnetoresistivities in Ta∕NiFe(t)∕IrMn (10 nm)∕Ta has been investigated for t=3, 4, 5, 7, 8, 10, 12, 15, and 20 nm by the method of anisotropic magnetoresistance and planar Hall effect. Our results revealed that the parallel and perpendicular resistivity components performed a varying function with increment in NiFe thickness. Both the resistivities at first were observed to increase when the NiFe thickness increases from 3 to 10 nm; then for the NiFe thicknesses from 10 to 20 nm, the resistivities of NiFe layer decrease as the NiFe thickness increases. However, the anisotropic resistivity change, which is the difference between parallel and perpendicular resistivities, was observed to increase for the whole range of thicknesses when the NiFe thickness increases. The measured quantities were found to be in good agreement with the theoretically estimated parameters using single domain model; thus these behaviors are well explained based on the modern...

Microstructure and Magnetic Properties of Au-doped Finemet-type Alloy

In this report, we demonstrate a comprehensive analysis of the effects of Au addition on the microstructure and magnetic properties of Fe 73.5 Si 13.5 B 9 Nb₃Au₁ Finemet-type alloy. It was found that the as-quenched alloys were the amorphous state and turned into nanocrystalline state under heat treatments. The DSC analysis indicates that the sharply exothermal peak corresponding to the crystallization of the α-Fe(Si) was observed at 547- 579℃ depending on the heating rates, which is little higher than that of original Finemet (542-570℃, respectively). Besides, the thermomagnetic result confirmed that the full substitution of Cu by Au with the single phase structure in the M(T) curve along cooling cycle. Ultrasoft magnetic properties of the nanocrystallized samples were significantly enhanced by the proper annealing such as the increase of permeability and the decrease of the coercivity. The optimum annealing condition was found at the annealing temperature of 540℃ and the increase of the annealing time up to 90 min.

Influences of rapid annealing and substrate temperature on the magnetic properties of Co-Fe-V films

In this paper we report the results of a systematic investigation of influences of the deposition conditions on the microstructure and magnetic properties of Co-Fe-V thin films. The magnetic softness was optimized when the thin films were deposited at a sputtering pressure of 2mTorr and a sputtering power density of 3.82W∕cm2. A strong modification in the coercivity and its shape with respect to film thickness and substrate temperature was observed. Nanocrystalline Co49.12Fe48.65V2.23 thin films exhibited the superior soft magnetic properties (Bs=25.7kG, Hc=1.2Oe, Hk=24.5Oe) and the high electrical resistivity of 300μΩcm, which are beneficial for high-frequency and temperature applications. It was also found that rapid annealing caused considerable changes in the microstructure and hence the magnetic properties of the Co-Fe-V thin films.

Effect of Annealing Temperature on the Permeability and Magneto-Impedance Behaviors of Fe 68.5 Mn 5 Si 13.5 B 9 Nb₃Cu₁ Amorphous Alloy

The effect of annealing temperature on the permeability and giant magneto-impedance (GMI) behaviors of Fe 68.5 Mn 5 Si 13.5 B 9 Nb₃Cu₁ amorphous alloy has been systematically investigated. The nan℃rystalline Fe68.5Mn5- Si13.5B9Nb3Cu1 alloys consisting of ultra-fine (Fe,Mn)₃Si grains embedded in an amorphous matrix were obtained by annealing their precursor alloy at the temperature range from 500℃ to 600℃ for 1 hour in vacuum. The permeability and GMI profiles were measured as a function of external magnetic field. It was found that the increase of both the permeability and the GMI effect with increasing annealing temperature up to 535℃ was observed and ascribed to the ultrasoft magnetic properties in the sample, whereas an opposite tendency was found when annealed at 600℃ which is due to the microstructural changes caused by high-temperature annealing. The study of temperature dependence on the permeability and GMI effect showed some insights into the nature of the magnetic exchange coupling between nan℃rystallized grains through the amorphous boundaries in nan℃rystalline magnetic materials.