Kyu-Han Lee

Electromagnetic wave absorption properties of amorphous alloy-ferrite-epoxy composites in quasi-microwave band

Reports on the electromagnetic wave absorption properties of amorphous alloy-ferrite-epoxy composites with various amorphous alloy fractions in the frequency range from 1 to 5 GHz. We varied the fraction of amorphous alloy in amorphous alloy-ferrite-epoxy composites from 0 to 50 vol.% at a fixed 50 vol.% fraction of epoxy resin polymer. We measured the complex permeability /spl mu/ and permittivity /spl epsiv/ of composites by the reflection/transmission technique, and determined the theoretical matching frequency and thickness with maximum reflection loss by plotting the measured /spl mu/ and /spl epsiv/ on an impedance matching solution map. The increasing amorphous alloy fraction in amorphous alloy-ferrite-epoxy composites resulted in a larger matching frequency and thinner thickness than those of ferrite-epoxy composite. On the basis of these results, we propose a new, thinner wave absorber, made by optimizing the amorphous fraction and thickness in amorphous alloy-ferrite-epoxy composites.

Enhancement of magnetoresistance in [Pd∕Co]N∕Cu∕Co∕[Pd∕Co]N∕FeMn spin valves

The dependences of the stack number and Co and Cu thicknesses on magnetoresistance, and perpendicular exchange biasing in the [Pd∕Co]×N1∕Cu∕Co∕[Pd∕Co]×N2∕FeMn spin valves, were investigated. The magnetoresistance ratio of the spin valves with N1=4 and N2=2 was above 5% for the Cu between 1.5 and 2.5nm, and the exchange-biasing field (Hex) was increased to 600Oe. When the Co thickness over the Cu layer was increased from 0.48to1.28nm, the ratio likewise rose to 7.4% due to the strengthened spin-dependent scattering effect. Moreover, the Co thickness below the Cu layer rose to 9.1%. The maximum ratio of 10.2% was obtained in the structure of the [Pd0.8∕Co0.32]×2∕Pd0.8∕CoFe0.48∕Cu2.25∕CoFe0.6∕[Pd0.8∕Co0.48]×2∕FeMn15 (nanometer) multilayer with Hex=450Oe.

A Pulse-type Hysteresis Loop Tracer For Rare Earth Based Permanent Magnets

Introduction Much work is currently under way on rare earth permanent magnets (NdFeB and SmCo based magnets) which exhibit large values of remanent magnetization, coercivity and energy product, compared to conventional magnets such as ferrites and AlNiCo [1]-[4]. With their excellent permanent magnetic properties particularly large coercivity, it is required to apply magnetic fields as large as 50 kOe for a full saturation; in this regards, the measurements of magnetic properties of rare earth based magnets have been a problem in the circles of research community by using conventional electromagnets which normally can generate maximum magnetic fields up to 20 kOe. The main aim of the present work is to generate pulse magnetic fields with bi-polarity and measure the whole hysteresis loop of a permanent magnet from a single measurement. The pulsed high magnetic fields with bi-polarity are generated by approaching the damping ratio of current amplitude to 1 when a large Capacitance charge is discharged into a solenoid. The generated bi-polar magnetic fields permit m measure minor loops as well as maior loous, and also to demametize the samples. ExDerimental A. The Basic Construction .,

Quantitation of Taurine and Selenium Levels in Human Milk and Estimated Intake of Taurine by Breast-Fed Infants during the early Periods of Lactation

With these results we report the following: Taurine levels in human milk decreased slightly during the early lactation period. The concentration of taurine (406 +/- 174 nmol/ml) in colostrum was significantly higher than that (335 +/- 115 nmol/ml) in mature milk. Selenium content of human milk also decreased slightly during the early lactation period. The content of selenium (28.6 +/- 19.6 ng/ml) in colostrum was significantly higher than that (1 5.1 +/- 5.9 ng/ml) in mature milk. A correlation was not found between the taurine and selenium content of human milk. The intake of taurine and selenium by breast-fed infants progressively increased with days postpartum. These results were due to the significant increase in milk intake by infants. It is suggested that the taurine and selenium levels in colostrum are more concentrated than those in mature milk. However, the absolute intake of taurine and selenium by infants are higher in mature milk.

Field sensitivity in spin-valve sandwiches with antiferromagnetic NiO films

We have investigated the MR ratios and the field sensitivities in Ni/sub 81/Fe/sub 15//Cu/Ni/sub 81/Fe/sub 19/ spin-valve sandwiches grown on antiferromagnetic NiO films as a function of the NiO thickness and the uniaxial deposition field. The MR ratio has a maximum value of 4.5% at 420 /spl Aring/ of NiO and 180 Oe of uniaxial deposition field, and a field sensitivity of 0.6%/Oe. In order to obtain a higher MR ratio and field sensitivity, we have studied the effects of adding a Co layer between the interfaces of NiFe and Cu and also the effects of a NiO film on top or at bottom on the spin-valve sandwiches. The MR sandwiches with the Co layer increases to 8.2%, however, the sensitivity decreases to 0.37%/Oe due to the high coercivity of Co. The Co inserted structure with the NiO film on top has a low MR ratio of 5.7% and a high sensitivity of 5.8%/Oe. The thermal stability of the sandwiches with the NiO film on top is superior to that of the NiO film at bottom.

Taurine Intake of Korean Breast-Fed Infants during Lactation

i. Taurine concentrations of human milk of nonvegetarians and lacto-ovovegetarians decreased significantly during the course of lactation. Taurine concentrations in lacto-ovovegetarians after 90 days postpartum were lower than those of nonvegetarians. Taurine concentrations of human milk by 150 days postpartum were: nonvegetarian 248-434 nmol/ml (31.0-54.4 mg/L); lacto-ovovegetarian 153-418 nmol/ml (19.1-52.3 mg/L). ii. Taurine intakes in infants of lacto-ovovegetarians decreased significantly during lactation, unlike from the pattern in infants of nonvegetarians. Taurine intakes in infants of lacto-ovovegetarians at 90, 120 and 150 days postpartum were lower, compared with those in nonvegetarians. Taurine intakes in infants by 150 days postpartum were: Infants of nonvegetarians 169-229 mumol/day (21.1-28.6 mg/day); Infants of lacto-ovovegetarians 106-210 mumol/day (21.1-28.6 mg/day). iii. This study showed that the taurine concentration in human milk and the taurine intake of infants were different during lactation between nonvegetarians and lacto-ovovegetarians, and that the intake per kg body weight decreased during lactation. Results suggest that the differences observed might be due to the effect of consumption of different types of food.

Determination of rotatable anisotropy in exchange-biased bilayers using anisotropic magnetoresistance technique

We improved the anisotropic magnetoresistance model to determine the quantity and direction of rotatable anisotropy in FeMn/NiFe structures independent of the thickness of the antiferromagnet layer. In our model, there are two important parameters, the magnitude α=Hrot/Hex and direction β=θrot/θa of rotatable anisotropy, where Hrot and θrot are an effective magnetic field and angle of a rotatable anisotropy, and Hex and θa are the exchange bias field and angle of applied field. As FeMn thickness decreased from 20 nm to 3.5 nm, α value increased from about 0.15 to 0.55. This proves that weak exchange coupling regions increase as the antiferromagnet thickness decreases. The α and β almost did not change as the NiFe thickness increases from 7 nm to 15 nm, even if the Hex was reduced from 170 Oe to 70 Oe.

Dependence of the Exchange Bias and Coercivity of [Pd/Ferromagnet]

The dependencies of the stack number N on perpendicular exchange-biasing (H_ex) and coercivity H_c) in [Pd/Co]_N and [Pd/Co (or CoFe)]_N/FeMn multilayers were investigated. With the help of the careful designs of layer structures, a series of samples whose surface anisotropies have the linear function N was prepared with constant bulk anisotropies. From the experimental data obtained, it was found that H_ex does not depend on the surface anisotropy, while H_c shows a strong dependence. Therefore, it is possible to tailor wide ranges of H_c (300-600 Oe) without varying H_ex(~200 Oe) through the single control parameter stack number N

_N

The local magnetization reversal of an exchange-biased in-plane FeMn/NiFe bilayers and out-of plane [Pd/Co]5/FeMn multilayers as a function of exposed region is investigated. The multilayer films are deposited using ion-beam and dc magnetron sputtering method. Laser annealing using a diode pumped solid state (Nd:YAG) laser is then utilized to locally reverse the unidirectional anisotropy in the films. The hysteresis loops for the exchange biased films are also analyzed by the magnetic optical Kerr effect and the extraordinary Hall effect.

/FeMn Multilayers on the Stack Number

Magnetoresistance and exchange coupling in spin-valve films using antiferromagnetic NiO/CuO/NiO trilayers were investigated. The exchange coupling field H/sub ex/ and MR ratio in the NiO/sub 300 /spl Aring///CuO/sub 300 /spl Aring///NiO/sub 300 /spl Aring///NiFe/sub 50 /spl Aring///Cu/sub 20 /spl Aring///NiFe/sub 50 /spl Aring// films were almost constant values of 100 Oe and 4.5% despite of the variation of the inserted CuO thickness, however, the coercive field H/sub c/ increased from 80 Oe to 270 Oe. The apparent increase in the coercive field with the inserted thickness of CuO layer is due to the increment of interface roughness between antiferromagnetic NiO/CuO/NiO and pinned NiFe layers.