• Journal of Astronomy and Space Sciences
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• v.33 no.3
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• pp.173-176
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• 2016

We report on a systematic analysis of the spin and superorbital modulations of the high-mass X-ray binary 4U 0114+650, which consists of the slowest spinning neutron star known. Utilizing dynamic power spectra, we found that the spin period varied dramatically during the RXTE ASM and Swift BAT observations. This variation consists of a long-term spin-up trend, and two ~1,000 day and one ~600 day random walk epochs previously, MJD 51,000, ~MJD 51,400-52,000, and ~MJD 55,100-56,100. We further found that the events appear together with depressions of superorbital modulation amplitude. This provides evidence of the existence of an accretion disk, although the physical mechanism of superorbital modulation remains unclear. Furthermore, the decrease of the superorbital modulation amplitude may be associated with the decrease of mass accretion rate from the disk, and may distribute the accretion torque of the neutron star randomly in time.

• Applied Science and Convergence Technology
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• v.23 no.3
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• pp.128-133
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• 2014

We study the ballistic spin transport properties in a two-dimensional electron gas system in the presence of magnetic barriers using a transfer matrix method. We concentrate on the size-effect of the magnetic barriers parallel to a two-dimensional electron gas plane. We calculate the transmission probability of the ballistic spin transport in the magnetic barrier structure while varying the width of the magnetic barriers. It is shown that resonant tunneling oscillation is affected by the width and height of the magnetic barriers sensitively as well as by the inter-spacing of the barriers. We also consider the effect of additional electrostatic modulation on the top of the magnetic barriers, which could enhance the current spin polarization. Because all-semiconductor-based devices are free from the resistance mismatch problem, a resonant tunneling structure using the two-dimensional electron gas system with electric-magnetic modulation would play an important role in future spintronics applications. From the results here, we provide information on the physical parameters of a device to produce well-defined spin-polarized current.

• Proceedings of the Korean Magnestics Society Conference
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• 2009.12a
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• pp.67-67
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• 2009

• Journal of the Korean Magnetic Resonance Society
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• v.6 no.1
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• pp.20-37
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• 2002

MnAPSO-34 and Mn-impregnated SAPO-34(Mn-SAPO-34) sample were prepared with various manganese contents and studied by electron spin resonance(ESR) and electron spin echo modulation(ESEM). Electron spin echo modulation analysis of 0.07mo1 ％ Mn(relative to p) in MnAPSO-34 with adsorbed D$_{2}$O shows two deuteriums at 0.26 nm and two at 0.36 nm from Mn. This suggests that two waters hydrate an MnO$_{4}$ configuration with a D-O bond orientation for the waters as expect for a negatively charged site at low manganese content (0.1 mol％), the ESR spectra of MnAPSO-34 and MnH-SAPO-34 exhibit the same parameters(g 2.01 and A 89 G), but the spectra obtained from MnAPSO-34 samples are better resolved. The decomposition temperature of as-synthesized MnAPSO-34 were in the range of 200-600 $^{\circ}C$ of the morpholine which is 12 $^{\circ}C$ higher than that in as-synthesized MnH-SAPO-34. Infrared spectra showed that the position of a band at 3450 $cm^{-1}$ / shifted about 15 $cm^{-1}$ / toward higher energy in MnAPSO-34 versus MnH-SAPO-34. The modulation depth of the two-pulse ESE of MnAPSO-34 with adsorbed D$_{2}$O is deeper than that of MnH-SAPO-34 with adsorbed D$_{2}$O. Three-pulse ESEM of MnAPSO-34 and MnH-SAPO-34 with adsorbed deuterium oxide shows that the local environments of manganese in the hydrated samples are different, suggesting that Mn(II) is framework substituted in MnAPSO-34 since it obviously occupies an extraframework position in MnH-SAPO-34.

• Proceedings of the Korean Magnetic Resonance Society Conference
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• 2002.08a
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• pp.80-80
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• 2002

MnPSO-34 and Mn-impregnated SAPO-34 (Mn-SAPO-34) sample were prepared with various manganese contents and studied by electron spin resonance (ESR) and electron spin-echo modulation (ESEM). Electron spin-echo modulation analysis of 0.07mol ％ Mn(relative to p) in MnAPSO-34 with adsorbed D$_2$O shows two deuteriums at 0.25 nm and two at 0.36 nm from Mn. This suggests that two waters hydrate an MnO4 configuration with a D-O bond orientation for the waters as expect for a negatively charged site at low manganese content (0.07 mol％), the ESR spectra of MnAPSO-34 and MnH-SAPO-34 exhibit the same parameters (g 2.02 and A 87 G), but the spectra obtained from MnAPSO-34 samples are better resolved. TGA of as-synthesized MnAPSO-34 shows that the decomposition temperature in the range 200-$600^{\circ}C$ of the morpholine is 12$^{\circ}C$ higher than that in as-synthesized MnH-SAPO-34. Infrared spectra shows that the position of a band at about 15 cm-1 toward higher energy in MnAPSO-34 versus MnH-SAPO-34. The modulation depth of the two-pulse ESE of MnAPSO-34 with absorbed D$_2$O is deeper than that of MnH-SAPO-34 with absorbed D$_2$O. Three-pulse ESEM of MnAPSO-34 and MnH-SAPO-34 with absorbed deuterium oxide shows that the local environments of manganese in the hydrated samples are different, suggesting that Mn(II) is framework substituted in MnAPSO-34 since it obviously occupies an extra-framework position in MnH-SAPO-34

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.595-597
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• 2015

LMC X-4 is an eclipsing high-mass X-ray binary exhibiting a superorbital modulation with a period of ~ 30:5 days. We present a detailed study of the variations of the superorbital modulation period with a time baseline of ~ 18 years. The period determined in the light curve collected by the Monitor of All-sky X-ray Image (MAXI) significantly deviates from that observed by the All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE). Using the data collected by RXTE/ASM, MAXI, and the Burst Alert Telescope (BAT) onboard Swift, we found a significant period derivative, $\dot{P}=(2.08{\pm}0.12){\times}10^{-5}$. Furthermore, the O{C residual shows complex short-term variations indicating that the superorbital modulation of LMC X-4 exhibits complicated unstable behaviors. In addition, we used archive data collected by the Proportional Counter Array (PCA) on RXTE to estimate the orbital and spin parameters. The detected pulse frequencies obtained in small time segments were fitted with a circular orbital Doppler shift model. In addition to orbital parameters and spin frequency for each observation, we found a spin frequency derivative of $\dot{v}=(6.482{\pm}0.011){\times}10^{-13}Hz{\cdot}s^{-1}$. More precise orbital and spin parameters will be evaluated by the pulse arrival time delay technique in the future.

• 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.

• Biophysical Society Newsletter
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• v.7 no.2
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• pp.10-18
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• 2001

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.12 no.4
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• pp.66-75
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• 2013

The spin modulation is proposed with modulating frequency and amplitude simultaeously, and realized with the array sturcture easily located due to the nanometer size of the spintronics oscillator. In this paper, the dual-channel receiver is deisgned for detecting the spin modulated signal. Resultly, we confirmed the dual-channel recevier well detected the data sent through the spintronics oscillator array, and processed up to 200 kbps on each channel. Distance is limited up to 1 cm due to the low level signal under -60 dBm. The realized dual-channel receiver has the size of $56{\times}33mm^2$.

• Journal of the Korean Magnetic Resonance Society
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• v.6 no.2
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• pp.118-131
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• 2002

Manganese-doped H-SAPO-34 samples were prepared by an ion-exchanged reaction between H-SAPO-34 and paramagnetic Mn(II) species in methanol media and characterized by ESR and Electron Spin-Echo Modulation(ESEM) studies. In the hydrated (W)MnH-SAPO-34 measured in water, the Mn(II) ion was octahedrally coordinated with four framework oxygens and two water molecules at a displaced site IV of the eight membered ring window in the ellipsoidal cavity, while the Mn(II) ion was octahedrally coordinated to three framework oxygens and three water molecules at a displaced site I' of the six membered ring window in the ellipsoidal cavity in hydrated(M)MnH-SAPO-34 measured in methanol. The similar result was found in the experiments with methanol adsorbents except ethanol.