• Journal of the Korean Magnetics Society
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• v.23 no.5
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• pp.154-158
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• 2013

We have analyzed the magnetization curves measures by using VSM and MOKE in synthetic antiferromagnetic coupled CoB/Ru/CoB thin film. The measured results were compared with calculated ones by Stoner-Wohlfarth model based on the magnetization behavior of two ferromagnetic layers ($M_1$, $M_2$). The calculated total magnetization ($M_{tot}=M_1+M_2$) and single layer magnetization($M_1$) behaviors were compared with measured results by using VSM and MOKE, respectively. The total magnetization curve ($M_{tot}=M_1+M_2$) showed reversible magnetization behavior with flopping field of about 50 Oe. While single layer magnetization ($M_1$) behaviors showed irreversible magnetization behavior in the field range of $H_F$ < H < $H_F$. These magnetization behaviors were explained by the angle difference between magnetization directions of two ferromagnetic layers in SAF sample.

• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.180-184
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• 2015

We have investigated the magnetization reversal behavior in ferromagnetic $Co_{0.5}Fe_{0.5}$ alloy films using the magneto-optical Kerr microscope capable of the direct observation of time-resolved domain patterns. Interestingly enough, as the sample thickness increases the magnetization reversal behavior becomes changed from a single domain wall motion to the random nucleations of domains. Also, from the stochastic analysis of the domain jump sizes during the domain wall motion, it was found that the magnetization reversal behavior in the samples shows the critical scaling behavior with the critical exponent of ${\tau}{\sim}1.33$.

• Journal of Magnetics
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• v.12 no.1
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• pp.17-20
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• 2007

We performed magnetic force microscopy (MFM) observation on array of Co dots in order to understand magnetic state and magnetization behavior of submicron sized Co dots patterned on GaMnAs bridge. MFM observations showed the magnetization reversal and processes of local magnetization of individual ferromagnetic Co nanodots. Magnetic state of Co dots either single domain or vortex is dependent on geometrical size and thickness. Transition from single domain to vortex state can be realized with MFM tip assisted local field. Magnetization reversal process takes place through sequential reversal of individual dots. Localized inhomogeneous magnetic field can be manipulated by controlling magnetic state of individual Co dot in the array structure.

• Journal of Magnetics
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• v.2 no.3
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• pp.93-95
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• 1997

We investigated the temperature dependence of magnetization of Fe/Al multilayers fabricated by dc magnetron sputtering system. As the temperature increased from 5 K in a low magnetic field (100G) the magnetization of the samples increased and made a broad peak at some critical temperature. Further increase of temperature decresed the magnetization as an ardinary ferromagnetic curve. Part of samples show rapid increase of magnetization at low temperature. A model developed in this study suggests that the biquadratic coupling yields such a rapidly increasing behavior of magnetization at low temperature.

• Journal of Magnetics
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• v.15 no.1
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• pp.29-31
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• 2010

We studied the magnetic properties of $TmFe_2O_4$. The magnetization measurements revealed the magnetic ordering of Fe spins at around 240 K. The difference between zero-field-cooled (ZFC) and field-cooled (FC) magnetization was close to the thermoremanent magnetization (TRM), indicating the glass behavior exhibited by this material.

• Journal of Magnetics
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• v.19 no.3
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• pp.215-220
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• 2014

This study investigates the dynamic magneto-mechanical behavior of magnetization-graded ferromagnetic materials Terfenol-D/FeCuNbSiB (MF). We measure the dynamic magneto-mechanical properties as a function of the DC bias magnetic field ($H_{dc}$). Our experimental results show that these dynamic magneto-mechanical properties are strongly dependent on the DC bias magnetic field. Furthermore, the dynamic strain coefficient, electromechanical resonance frequency, Young's moduli, and mechanical quality factor of Terfenol-D/FeCuNbSiB are greater than those of Terfenol-D under a lower DC bias magnetic field. The dynamic strain coefficient increases by a factor of between one and three, under the same DC bias magnetic field. In particular, the dynamic strain coefficient of Terfenol-D/FeCuNbSiB at zero bias achieves 48.6 nm/A, which is about 3.05 times larger than that of Terfenol-D. These good performances indicate that magnetization-graded ferromagnetic materials show promise for application in magnetic sensors.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.655-658
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• 1995

Magnetization behavior of sputter-deposited Co/Pd multilayers were characterized, and it has been found that even when the multilayers are sputtered at low pressure (10 mTorr), the coercivity of the multilayers can be increased to large extent without noticeable change of saturation magnetization by increasing the deposition pressure of Pd underlayer. It turned out that the surface topology of Pd underlayer gets rough as deposition pressure increases, which consequently affects the magnetization reversal mode of Co/Pd multilayers from domain wall motion to magnetic spin rotation. The enhancement of coercivity is attributed to the domain wall pinning effect which is comected with the surface roughness of Pd underlayer on which Co/Pd multilayers grow.

• Journal of Magnetics
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• v.9 no.4
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• pp.113-115
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• 2004

The magnetization properties have been measured for amorphous $Fe_{82}Mn_{8-x}B_xZr_{10}$ (x = 0-8) alloys. The temperature dependence of magnetization for these alloys shows the existence of antiferromagnetic couplings between Fe atoms in low fields at low temperatures. The magnetic parameters, obtained from the magnetization behavior are consistent with the presence of mixed magnetic state. The Curie temperature and magnetic moment increased with an increase of the concentration of B and spin glass like transition observed at low temperature decreases and finally vanishes at x = 8 at %. Our result suggests that the substitution of B for Mn seems to cause an increase of magnetic order.

• Journal of Powder Materials
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• v.10 no.2
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• pp.83-88
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• 2003

Nanocrystalline materials of Ni and Ni-Cu alloy have been synthesized by the pulsed wire evaporation (PWE) method and these abnormal magnetic properties in the magnetic ordered state have been characterized using both VSM and SQUID in the range of high and low magnetic fields. Ni and Ni-Cu particles with an average size of 20 to 80 nm were found to influence magnetic hysterisis behavior and the results of powder neutron diffraction patterns and saturation magnetization curves are shown to indicate the absence of the NiO phase. The shifted hysterisis loop and irreversibility of the magnetization curve in the high field region were observed in the magnetic-ordered state of both Ni and Ni-Cu. The virgin magnetization curve for Ni slightly spillover on the limited hysterisis loop ($\pm$20kOe). This irreversibility in the high field of 50 kOe can be explained by non-col-linear behavior and the existence of the metastable states of the magnetization at the surface layer (or core) of the particle in the applied magnetic field. Immiscible alloy of Cu-Ni was also found to show irreversibility having two different magnetic phases.

• Journal of Magnetics
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• v.8 no.3
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• pp.108-112
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• 2003

We report the experimental finding that there exists a transition of magnetization reversal process with varying the applied field in Co/Pd multilayer. We have measured the wall-motion speed V and the nucleation rate R during magnetization reversal via time-resolved direct domain observation, where the magnetization reversal process of Co/Pd multilayer is found to take a transition from thermal activation process to viscous process at the critical field of about 1.87 H$\_$C/ (coercivity). In the thermal activation regime, we find that the field dependences of two activation volumes for the wall-motion process and the nucleation process are different with each other, which reveals that the wall-motion and nucleation experience completely different interactions. In the viscous regime, we find that the wall-mobility is much smaller than a typical value for the sandwiched Co films, which implies that the Co/Pd interfaces in multilayer substantially contribute to the dynamic dissipation.