Tae-Sick Yoon

Coercivity enhancement by Zn addition in hot deformed NdFeB magnets

Anisotropic NdFeB magnets were fabricated by the single-stage hot deformation method from commercial isotropic MQPA powder. The effect of Zn addition on the magnetic properties was investigated and the considerable increase of coercivity was observed. The increment of coercivity was about 57% in the case of 0.4 wt% Zn addition compared with that for additive-free magnets.

The temperature dependence of the anisotropic Nd-Fe-B fabricated by single-stage hot deformation

Abstract Anisotropic Nd–Fe–B magnets were fabricated by a single-stage hot deformation process. In this study, the temperature characteristics of the single-stage hot deformed Nd–Fe–B magnets were investigated. The temperature coefficient of B r is −0.12%/°C, similar to those of isotropic MQPA powder, die-upset and sintered Nd–Fe–B magnets. The temperature coefficient of H ic is −0.72%/°C, which is about twice as high as isotropic MQPA (−0.38%/°C), and slightly higher than those of die-upset and sintered Nd–Fe–B magnets.

Local Current Distribution in a Ferromagnetic Tunnel Junction Fabricated Using Microwave Excited Plasma Method

Ferromagnetic tunnel junctions were fabricated by dc magnetron sputtering and plasma oxidation process. The local transport properties of the ferromagnetic tunnel junctions were studied using contact-mode Atomic Force Microscopy (AFM) and the local current-voltage analysis. Tunnel junctions with the structure of sub./Ta/Cu/Ta/NiFe/Cu/Mn75/Ir25//Co70/Fe30//Al-oxide were prepared on thermally oxidized Si wafers. Al-oxide layers were formed with microwave excited plasma using radial line slot antenna (RLSA) for 5 and 7 sec. Kr gas was used as the inert gas mixed with gas for the plasma oxidization. No correlation between topography and current image was observed while they were measured simultaneously. The local current distribution was well identified with the distribution of local barrier height. Assuming the gaussian distribution of the local barrier height, the ferromagnetic tunnel junction with longer oxidation time was well fitted with the experimental results. As contrast, in the case of the shorter time oxidation junction, the current mainly flow through the low barrier height area for its insufficient oxygen. Such leakage current might result in the decrease of tunnel magnetoresistance (TMR) ratio.

Annealing effect on the longitudinal and transverse incremental permeability in FeSmO thin films

The transverse permeability ratio (TPR) and longitudinal permeability ratio (LPR) as a function of an external field of FeSmO films have been investigated in conjunction with thermal treatment. The FeSmO films were prepared by the RF magnetron sputtering method in Ar atmosphere. The film annealed at 500°C has the maximum value of the incremental permeability ratio (PR) due to the ultrasoft magnetic materials. The LPR curve shows the single-peak pattern, and the TPR curve shows the double-peak pattern indicating the existence of the magnetic anisotropy effect. The magnetic anisotropy and the magnitude of the incremental permeability are strongly dependent on the magnetic softness due to the annealing. The large changes of LPR and TPR in low external fields can be useful for the evaluation of the magnetic softness as well as the magnetic sensor applications.

Mumetal Growing Temperature Effect on the Exchange Coupling of Cu/mumetal/Al Oxide/Co/Cu Multilayers

Magnetic multilayers of a ferromagnetic (FM)/insulator (I)/ferromagnetic (FM) structure have been studied to investigate magnetic exchange coupling between two FM layers. As the Mumetal (Ni_(77)Fe₁₄Mo_5Cu ₄ wt%) growth temperature increases, the grain size and the surface roughness increase simultaneously. The smallest coupling field is obtained at 40℃ where the grain size is larger than that of the 20℃ sample. The exchange coupling field increases again at temperatures higher than 40℃ due to increase in the surface roughness of the Mumetal.

Anisotropic Magnetoresistance Analysis of Permalloy Film Using 2-dimensional Magnetization Vector Measurement

We measured in-plane 2 dimensional magnetization vector using two pick-up coil sets and investigate the relationship between magnetization vector and anisotropic magnetoresistance. We can determine magnetization vector by measuring magnetic moment in x and y direction simultaneously. As the uniaxial magnetic anisotropy of permalloy film increases, magnetoresistance approaches the expectation which is calculated from the angle between current vector and magnetization vector. Magnetoresistance ratio is linearly proportional to the y moment magnitude which is parallel to the current direction

Effect of underlayer microstructure on the exchange coupling of Mumetal-Al oxide-Co multilayer

Summary form only given. Magnetic tunnel junction (MTJ) composed of ferromagnetic (FM1)/insulator (I)/ ferromagnetic (FM2) layer have investigated for years because it is believed to realize new and high performance magnetic sensor and memory devices. Flat interfaces were required to get best performance without orange peel coupling between FM1 and FM2. This article shows the cross-sectional TEM image of MTJ multilayer. The large curvature of insulator layer is shown at the grain boundary region of FM1. For this purpose, we tried to decrease grain boundary density /spl zeta/ per unit area by increasing grain size of FM1. Then switching field of Mumetal, Hsw1 and exchange coupling field, Hex were measured to see the change of interlayer coupling state.

Soft magnetic properties of FeSmO thin films

The magnetic properties of FeSmO films have been investigated in conjunction with thermal treatment. The FeSmO films were prepared by the RF magnetron sputtering method in Ar atmosphere. The film annealed at 500°C had the good soft magnetic properties due to the grain growth of α-Fe.