• Journal of the Korean Magnetics Society
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• v.14 no.3
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• pp.105-108
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• 2004

Array of magnetic Ni nanostructures has been fabricated on Si substrate by using nanoporous alumina film as a mask during deposition. The nanostructures are truncated cone-shape and the lateral sizes are comparable to height. While the continuous film shows well-defined in-plane magnetization, the nanostructure shows perpendicular component of magnetization at remanence. The hysterectic behavior of nanostructures is dominated by the demagnetizing field instead of interaction among them.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.141-141
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• 2000

In situ surface magneto-optic Kerr effect(SMOKE), X-ray photoelectron spectroscopy(XPS) and low energy electron diffraction(LEED) were used to study magnetic and structural properties of ultrathin Fe films grown on the Pd(111) surface. The SMOKE measurement showed strong enhancement of ferromagnetism after proper annealing process. Simultaneous changes in morphology was checked by LEED and XPS. After room temperature Fe deposition. longitudinal magnetization appeared above a critical thickness between 2.0 and 2.5 monolayers. When annealed at 450K, 2.0 monolayer Fe film exhibited boty longitudinal and polar magnetizations while 3.0 and 5.5 monolayer films showed little changes. After annealing at 600K, both magnetizations were totally destroyed in 2.0 monolayer film, but longitudinal magnetization was enhanced in 3.0 monolayer film. In the case of 5.5 monolayer film, it was only after 660K annealing that the enhancement of the longitudinal magnetization was observed. It was concluded that the surface flatness and the amount of intermixing were critical in the development of surface magnetism of this system.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.230-238
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• 2000

We present the magnetisation reversal dynamics of epitaxial Fe thin films grown on GaAs(001) and InAs(001) studied as a function of field sweep rate in the range 0.01-160 kOe/s using magneto-optic Kerr effect (MOKE). For 55 and 250 ${\AA}$ Fe/GaAs(001), we find that the hysteresis loop area A follows the scaling relation A ∝ H$\^$${\alpha}$/ with ${\alpha}$=0.03∼0.05 at low sweep rates and 0.33-0.40 at high sweep rates. For the 150 ${\AA}$ Fe/InAs(001) film, ${\alpha}$ is found to be ∼0.02 at low sweep rates and ∼0.17 at high sweep rates. The differing values of ${\alpha}$ are attributed to a change of the magnetisation reversal process with increasing sweep rate. Domain wall motion dominates the magnetisation reversal at low sweep rates, but becomes less significant with increasing sweep rate. At high sweep rates, the variation of the dynamic coercivity H$\sub$c/ is attributed to domain nucleation dominating the reversal process. The results of magnetic relaxation studies for easy-axis reversal are consistent with the sweeping of one or more walls through the entire probed region (∼100 $\mu\textrm{m}$). Domain images obtained by scanning Kerr microscopy during the easy cubic axis reversal process reveal large area domains separated by zigzag walls.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.1
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• pp.89-98
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• 2002

Optical current sensor and optical voltage sensor modules were designed and fabricated to improve measurement error and insulation in automatic power distributor By using Faraday effect, optical current sensor with an $\alpha$-iron core was designed and fabricated to minimize current induction of the other phase and was optimized to maintain linearity. Optical voltage sensor was fabricated owing to the pockets effect and adopted spatial electric field type because of small room in an automatic power distributor. To connect a distributor with an external terminal for signal processing, optical multi connector was designed, fabricated and tested for coupling loss and gas leakage. The linearity of optical current sensor for applied current maintains variation of smaller than 2.5% for applied current range from 20A to 700A. The linearity of optical voltage sensor was smaller than 1% for appling voltage from 6.6kV to 19.8kV. Since the measured characteristics are good, these devices can be considered as being applicable in practice.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.369-373
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• 2003

Magneto-optic Kerr Effect(MOKE), AFM and magnetoresistance measurements have been carried out on as-deposited and annealed Magnetic Tunnel Junctions(MTJs) with junction sizes 180, 250, 320 and 380 $\mu\textrm{m}$ in order to investigate the correlation among interlayer exchange coupling, surface roughness and junction size. Relatively irregular variations of coercivity $H_{c}$ (∼17.5 Oe) and interlayer exchange coupling $H_{E}$ (∼17.5 Oe) are observed over the junction in as-deposited sample prepared by DC magnetron sputtering. After annealing at $200^{\circ}C$, $H_{c}$ decreases to 15 Oe, while $H_{ E}$ increases to 20 Oe with smooth local variation. $H_{E}$ shows very good correlation with surface roughness across the junction in agreement with Neel's orange peel coupling. The increasing slope per $\mu\textrm{m}$ of normalized $H_{c}$ and $H_{E}$ are same near junction edge along free-layer direction irrespective of junction size, giving relatively uniform $H_{c}$ and $H_{ E}$ for wider junction size. Thickness profiles of the junctions measured with $\alpha$-step show increasingly flat top surface for larger junctions, indicating better uniformity for large. junctions in agreement with the normalized$ H_{c}$ and H$/_{E}$ curves. TMR ratios also increase with increasing junction size, indicating improvement for larger uniform junctions.

• Proceedings of the Korean Magnestics Society Conference
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• 2011.12a
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• pp.7-8
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• 2011

Although yttrium iron garnet (YIG) has provided a great vehicle for the study of spin waves in the past, associated difficulties in film deposition and device fabrication using YIG had limited the applicability of spin waves to practical devices. However, microfabrication techniques have made it possible to characterize both the resonant as well as the travelling characteristics of spin waves in permalloy (Py). A variety of methods have been used for measuring spin waves, including Brillouin light scattering (BLS), magneto-optic Kerr effect (MOKE), vector network analyzer ferromagnetic resonance (VNA-FMR), and pulse inductive microwave magnetometry (PIMM). PIMM is one of the most preferred methodologies of measuring travelling spin waves. In this method, an electrical impulse is applied at one of two coplanar waveguides patterned on top of oxide-insulated Py, producing a local disturbance in the magnetization of the Py. The resulting disturbance travels down the Py in the form of waves, and is inductively picked up by the other coplanar waveguide. We investigate the effect of the pulse width of excitation pulses on the generated spin wave packets using both experimental results and micromagnetic simulations. We show that spin wave packets generated from electrical pulses are a superposition of two separate spin wave packets, one generated from the rising edge and the other from the falling edge, which interfere either constructively or destructively with one another, depending upon the magnitude and direction of the field bias conditions. A method of spin wave amplitude modulation is also presented by the linear superposition of spin waves. We use interfering spin waves resulting from two closely spaced voltage impulses for the modulation of the magnitude of the resultant spin wave packets.

• Journal of Magnetics
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• v.6 no.2
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• pp.47-52
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• 2001

We present the magnetisation reversal dynamics of epitaxial Fe thin films grown on GaAs(001) and InAs(001) studied as a function of field sweep rate in the range 0.01-160 kOe/s using magneto-optic Kerr effect (MOKE). For 55 and 250 ${\AA}$ Fe/GaAs(001), we find that the hysteresis loop area A follows the scaling relation $A\propto H_{\alpha} \;with\; \alpha=0.03\sim0.05$ at low sweep rates and 0.33~0.40 at high sweep rates. For the 150${\AA}$ Fe/InAs(001) film, $\alpha$is found to be ~0.02 at low sweep rates and ~0.17 at high sweep rates. The differing values of $\alpha$ are attributed to a change of the magnetisation reversal process with increasing sweep rate. Domain wall motion dominates the magnetisation reversal at low sweep rates, but becomes less significant with increasing sweep rate. At high sweep rates, the variation of the dynamic coercivity $H_c{^*}$ is attributed to domain nucleation dominating the reversal process. The results of magnetic relaxation studies for easy-axis reversal are consistent with the sweeping of one or more walls through the entire probed region (~100$\mu m$). Domain images obtained by scanning Kerr microscopy during the easy cubic axis reversal process reveal large area domains separated by zigzag walls.