• Journal of Magnetics
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• v.3 no.4
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• pp.105-111
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• 1998

The low energy excitations of spin waves (SWR) in thin films can be used for determination of the surface anisotropy constant and the nonhomogeneities of magnetization in the close-to-surface layer. The dispersion relation in SWR is sensitive on the geometry of experiment. We report on temperature dependence of surface magnetic anisotropy energy constant in magnetic semiconductor thin films of$ CdCr_{2-2x}In_{2x}Se_4$ at spin glass state. Samples were deposited by rf sputtering technique on Corning glass substrate in controlled temperature conditions. Coexistence of the infinite ferromagnetic network (IFN) and finite spin slusters (FSC) in spin glass state (SG) is know phenomena. Some behavior typical for long range magnetic ordering is expected in samples at SG state. The spin wave resonance experiment (microwave spectrometer at X-band) with excited surface modes was applied to describe the energy state of surface spins. We determined the surface magnetic anisotropy energy constant versus temperature using the surface inhomogeneities model of magnetic thin films. It was found that two components contribute to the surface magnetic anisotropy energy. One originates from the exchange interaction term due to the lack of translation symmetry for surface spin as well as from the originates from the exchange interaction term due to the lack of translation symmetry for surface spin as well as from the stray field of the surface roughness. The second one comes from the demagnetizing field of close-to surface layer with grad M. Both term linearly decrease when temperature is increased from 5 to 123 K, but dominant contribution is from the first component.

• Journal of Magnetics
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• v.12 no.1
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• pp.27-30
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• 2007

Experimental evidence suggests that spin pinning conditions for standing spin mode in polycrystalline $Ni_{84}Fe_{16}$ alloy film, is confirmed using the four categories of Camley et al. and the value of q$\bot$ for the pinning conditions, this was achieved by performing Brillouin light scattering measurements. The value of q$\bot$ was observed, in order to increase at a rate of $\pi$/2 with an increasing mode number. With this condition, the coexistence of standing spin wave modes was shown, with intermediate pinning, in addition to free and strong pinning. The values for spin-wave-stiffness constant ($D_B$), g-factor (g), and surface magnetization (4$\pi$M) of the Permalloy film were obtained from the results of BLS, and determined to be $D_B=1.85{\pm}0.05Oecm^2$, $g=2.11{\pm}0.02$, and 4$\pi$M=8.7 kG, respectively.

• Journal of the Korean Magnetics Society
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• v.21 no.4
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• pp.121-126
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• 2011

Spin dynamics of magnetic tunnel junctions with free and fixed reference layers is investigated by ferromagnetic resonance micromagnetic simulations. First, in magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer, a magnetization direction of each layer and the tunneling magnetoresistance are calculated for a DC magnetic field. To investigate the spin exciting modes in magnetic tunnel junctions, we simulate the ferromagnetic resonance frequency spectra with small RF magnetic fields. Exciting modes of the tunneling magnetoresistance calculated by an included angle between free and reference layers is interpreted from those of each layer. Spin exciting modes are different according to a signs of the DC magnetic field. In a negative magnetic field, FMR frequency spectra of free and reference layers are well elucidated by the modified Kittel's equation. However, in a positive magnetic field, there is no simple analytic solution related to FMR frequency spectra due to the coupled modes. Since ferromagnetic layers in magnetic tunnel junctions are interactive each other, careful considerations of the reference and fixed layer as well as the free layer are required for understanding on the spin dynamics of magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer.

• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.633-638
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• 2014

We report experimental behaviors of condensed $^{87}Rb$ atoms responding to changes in the trap potential of the atomchip. The two-types of adiabatic and non-adiabatic overall changes were implemented by changing the ramp-down speed of the chip-wire current, which can dominantly modify the one-axis magnetic field gradient. Under the adiabatic process, a pure condensate stayed in the initial spin state and collectively oscillated with both monopole and dipole modes, while an atomic cloud above the critical temperature exhibited sound waves in a dense ultracold gas. On the other hand, Bose-Einstein condensate atoms with non-adiabatic perturbation were split into spatially different positions by spin states through spin-flip. We investigated the split ratio among spin states depending on final evaporation frequency. Potential changes, of course, cause collective oscillations regardless of the changing process.

• Journal of the Korean Magnetics Society
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• v.24 no.6
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• pp.165-170
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• 2014

We analyzed the ferromagnetic and spin wave resonance signals measured in amorphous CoFeB thin films with different thickness. The ferromagnetic resonance field ($H_{FMR}$) was not depend on the thickness of CoFeB films, but the spin wave resonance field ($H_{SWR}$) was well fitted with the theoretical prediction depending on the thickness. The uniaxial anisotropy field of $H_k$ = 37 Oe was obtained from the angular dependent $H_{FMR}$ in CoFeB films. The $H_{SWR}$ showed same angular behaviors with $H_{FMR}$, however, the amplitude of spin wave resonance signals showed 5.7 times higher than that of ferromagnetic resonance signals in CoFeB film with t = 100 nm. The higher signals were due to the two reasons; one was the small damping for the spin wave propagation without degradation, the other was uniform magnetization for the ideal standing wave modes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.60-60
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• 2011

Giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), and magnetic random-access memory (MRAM) are currently active research areas in spintronics. The high magnetoresistance and the high spin polarization (P) of electrons in the ferromagnetic electrodes of tunnel junction or intermediate layers are required. Magnetite, Fe3O4, is predicted to possess as half-metallic nature, P ~ 100% spin polarization, and has a high Curie temperature (TC~850 K). Experiments demonstrated that the P~($80{\pm}5$)%, ~($60{\pm}5$)%, and ~40-55% for epitaxial (111), (110) and (001)-oriented Fe3O4 thin films, respectively. Epitaxial Fe3O4 films may enable us to investigate the effects of half metals on the spin transport without grain-boundary scattering.In addition, it has been reported that the Verwey transition (TV, a first order metal-insulator transition) of 120 K in bulk Fe3O4 is strongly affected by many parameters such as stoichiometry and stress, etc. Here we report that the growth modes, magnetism and transport properties of Fe3O4 thin films were strongly dependent on the oxygen pressure during film growth. The average roughness decreases from 1.021 to 0.263 nm for the oxygen pressure increase from $2.3{\times}10-7$ to $8.2{\times}10^{-6}$ Torr, respectively. The 120 K Verwey transition in Fe3O4 was disappeared for the sample grown under high oxygen pressure.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.524-527
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• 1995

The temperature dependence of spin wave mode separation in amorphous $Co_{89.5}Zr_{10.5}$ thin film has been investigated at temperatures between 100 K and 300 K. The magnetization and the spectroscopic splitting factor were obtained for the main resonance mode in parallel and perpendicular magnetic field. ${\Delta}H_{2-3}$, the difference between resonance field of mode 2 and the resonance field of mode 3, increases with decreasing temperature. The linewidth increases for all the modes with decreasing temperature. Especially in mode 3 it increases rapidly below 200 K. This phenomenon could be caused by the increase of exchange stiffness constant or the decrease of surface magnetic anisotropy constant with decreasing temperature.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.279-284
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• 1996

Decay of the spin label attached to cytochrome c or to stearic acid has been measured by electron paramagnetic resonance (EPR) spectroscopy to monitor membrane oxidation induced by cytochrome c-membrane interaction. Binding of cytochrome c sequestered the acidic phospholipids and membrane oxidation was efficient in the order linoleic oleic>stearic acid for a fatty acid chain in the acidic phospholipids. The spin label on cyt c was destroyed at pH 7 whereas that on stearic acid embedded in the membrane was destroyed at pH 4, presumably due to different modes of cyt c-membrane interaction depending on pH. Interestingly, cyt c also interacts with phosphatidylethanolamine, an electrically neutral phospholipid, to cause rapid membrane oxidation. Both EPR and fluorescence measurements indicated that electrostatic interaction is at least partially responsible for the process.

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.265-274
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• 1994

Intermetallic Ti-Si system ceramics were synthesized from stochiometric mixtures of titanium and silicone powders in vacuum by Self-propagating High-temperature Synthesis(SHS). In each cases of Ti5Si3, Ti5Si4 and TiSi, and TiSi2 synthesis, 20wt% product dilution, direct ignition and SHS chemical furnace method were employed. The combustion modes, which were observed during the synthesis process by using the high speed camera, of Ti5Si3, Ti5Si4, TiSi, and TiSi2 exhibit spin, osciallatory, steady-state, and spin combustion, respectively. With increasing Ti/Si molar ratio an decrease of combustion velocities was found. From the results on the measurement of the flexural strength, the specimen hot pressed at 135$0^{\circ}C$ for 30 min using synthesized Ti5Si4 powders showed the highest flexural strength at 215 MPa.

• Journal of the Korean Magnetics Society
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• v.4 no.1
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• pp.1-6
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• 1994

The magnetization dynamics was investigated by solving possible origins of overdamped susceptibility observed in ultra-soft magnetic amorphous thin films. The experimental high frequency spectrum and computational spectrum calculated from Gilbert's equation of motion were compared in order to find proper damping factor $\alpha{\approx}20$ and demagnetizing coefficients $D_{x}{\approx}D_{y}{\approx}D_{z}{\approx}0$ for ultra-soft magnetic films. A magnetization vortex mode was, then, proposed to explain the origin of the reversible susceptibility and other anomalies of the ultra-soft magnetic heterogeneous thin films. In this mode it is suggested that there occur, within the nanoscale structural features of the ultra-soft films, incoherent rotational spin motions that are highly damped by the energy transfer from short wavelength spin wave modes and local defect structure mode interactions.