Kwang Youn Kim

Low Temperature Magnetizaiton In Nanocrystalline Fe/sub 88/ Zr/sub 7/ B/sub 4/ Cu/sub 1/ Alloy

The authors report on the effect of annealing temperatures on the spin wave excitations for the nanocrystalline Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/ alloy, observed from the low-temperature magnetization curve and the spectroscopic splitting g factor. The thermomagnetization curve at low temperature is found to obey the Bloch law, M/sub s/(T)=M/sub s/(0)(1-BT/sup 3/2/-CT/sup 5/2/). From these experimental results, spin wave stiffness constants within the annealing condition are calculated. The effective permeability, coercive force, saturation magnetization (B/sub 10/), magnetostriction and magnetic anisotropy of the annealed alloys are studied systematically. >

Improved Magnetic Properties of Silicon-Iron Alloy Powder Core

Eventhough Fe-6.5 wt.% Si alloy shows excellent magnetic properties, magnetic components made of the alloy with the composition are not totally commercialized because of its extremely low ductility. In order to overcome this demerit of alloy, 6.7 wt.% Si alloy powders were produced by gas atomization and then post-processed to form magnetic cores. By doing so, the total core loss could be minimized by reducing both hysteresis and eddy current loss, which were attributed to both grain size adjustment and particle size control. From our experiments, we were able to achive a core loss of 390 mW/cm3 at an induction of 0.1 T and 50 kHz through proper processes and a permeability μeff of 68 at low frequency was kept up to 700 kHz. These properties are compatable with the properties of well-known soft magnetic materials such as Fe-Si-Al and Ni- Fe alloys. From the above results, it can be concluded that Fe-Si alloy powders with high Si content have very high potential for the commercialization and application of the core.

Spin wave excitation on amorphous Co80+xTM12B8-x alloys

Abstract Amorphous Co80+xTM12B8-x (TM = Ti, Zr, Hf, Nb; x = 0, 2, 4 at%) alloys were prepared by the single-roller melt-spinning technique. The saturation magnetization of the amorphous ribbons was measured by a SQUID and a vibrating sample magnetometer at 5–800 K under an applied field of 10 kOe. Typical thermo-magnetization curves were observed, and average values of the spectroscopic splitting g factor were estimated from the ferromagnetic resonance (FMR) curve. For all the amorphous alloys studied here, the saturation magnetization in the temperature range 5 K up to about 0.3TC can be described by the Bloch relation, M s (T) = M s (0)(1 − BT 3 2 - CT 5 2 ) . The spin wave stiffness constants were calculated from the values of Ms(0), B and the spectroscopic splitting g factor.

Spin wave stiffness constants of amorphous Fe-Zr-B-Nb alloys

Abstract We have investigated the magnetic properties of amorphous Fe 83− x Zr 7 B 10 Nb x alloys, which possess potentially interesting properties as high frequency core materials due to its high effective permeability and low coercive force. The temperature dependence of magnetization were measured with a SQUID magnetometer and g values were deduced from a ferromagnetic resonance (FMR) experiment. The low temperature magnetization curve is found to obey Blochs T 3/2 law. From these experimental results, spin wave stiffness constants were calculated.

Spin-Polarized Hot Electron Injection into Two-Dimensional Electron Gas by Magnetic Tunnel Transistor

A magnetic tunnel transistor has been fabricated on top of a modulation-doped GaAs/AlGaAs heterostructure that provides a high-mobility two-dimensional electron gas. The emitter and base of the magnetic tunnel transistor consisted of a ferromagnetic metal, whereas the collector consisted of the two-dimensional electron gas. Spin polarized hot electrons from the emitter were filtered by the CoFe base layer and then injected into the collector, leading to a finite magnetocurrent ratio. The magnetocurrent ratio decreased as the hot electron energy was increased by increasing the bias voltage between the emitter and the base above a certain threshold voltage. We observed magnetocurrent ratios of ~27% at 17 K and ~2% at 300 K, indicating that spin-polarized hot electrons are injected into the two-dimensional electron gas from 17 K up to room temperature.

The Fabrication and Magnetoresistance of Nanometer-sized Spin Device Driven by Current Perpendicular to the Plane

In order to make submicron cell for spin-injection device, lift-off method using Pt stencil and wet etching was chosen. This approach allows batch fabrication of stencil substrate with electron-beam lithography. It simplifies the process between magnetic film stack deposition and final device testing, thus enabling rapid turnaround in sample fabrication. Submicron junctions with size of and 500 nm and pseudo spin valve structure of ) was deposited into the nanojunctions. MR ratio was 0.8 and , respectively and spin transfer effect was confirmed with critical current of .

The Dependences of Magnetoresistance and Exchange Biasing on Annealing temperature in Top and Bottom Type Specular Spin Valves with Nano-oxide Layers

We investigated magnetoresistance(MR) and exchange bias properties by annealing in top and bosom type spin valves (SV) with nano-oxide layers (NOL). In top SVs with NOL, MR ratio of 9.2% is obtained after postdeposition annealing at 250. In bottom SVs with NOL, MR ratio of 10.1 % is obtained after postdeposition annealing at 250. Therefore, specular reflection of the NOL in bottom SVs is higher than that of the NOL in top SVs. Exchange biasing of bottom SVs with NOL is 28% higher than that of bottom SVs without NOL after annealing. This enhancement of exchange biasing is thought to be due to the reduced magnetic moment of the pinned layer with NOL and enhanced (111) FeMn texture.∌簀؀歯獨慭ሀ鳪떭ꧬ麬駭验

Magnetic properties of the amorphous Fe-Zr-B-Ni alloys annealed below the crystallization temperature

We have studied the magnetic properties of amorphous Fe/sub 83-x/Zr/sub 7/B/sub 10/Ni/sub x/ alloys annealed below the crystallization temperature. Such materials are considered to have a potential for high frequency core material applications because of possibilities of obtaining high effective permeability and low coercive force. The addition of Ni content of approximately 0.5-1.5 at.% was found to be effective in improving the soft magnetic properties. The temperature dependence of magnetization measured by a SQUID magnetometer are found to be in good agreement with the spin wave theory. The spectroscopic splitting g values obtained by ferromagnetic resonance (FMR) experiments increase with increasing Ni content. The values of the spin wave stiffness increases from 62.7 meV /spl Aring//sup 2/ to 95.2 meV /spl Aring//sup 2/ with increasing the concentration of Ni. From these experimental results, the range of the exchange interaction are deduced.