• Journal of the Korean Magnetics Society
• /
• v.13 no.1
• /
• pp.21-28
• /
• 2003

M-type hexagonal BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$ (0$\leq$x$\leq$1.0) ferrite powders prepared by a sol-gel method. The crystallographic and magnetic properties were characterized with a x-ray diffraction (XRD), thermogravimetry (TG), differential thermal analysis (DIA), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and Mossbauer spectroscopy. The result of XRD measurements show that the a and c lattice parameters increase with increasing x from $\alpha$=5.882 and c=23.215 $\AA$ for $\chi$=0.0, to $\alpha$=5.895 and c=23.295 $\AA$ for $\chi$=1.0. From the Mossbauer results, the $Co^{2+}$- $Ti^{4+}$ site occupancies have been affected the changes in the magnetization and in the coercivity. The Curie temperature linearly decreases with increasing $Co^{2+}$- $Ti^{4+}$ concentration x.

• Investigative Magnetic Resonance Imaging
• /
• v.13 no.2
• /
• pp.127-136
• /
• 2009

Purpose : Functional magnetic resonance imaging (fMRI) was used to assess the temporal response of neural activation in healthy subjects while they performed the Iowa Gambling Test (IGT), which utilizes decisions involving ambiguity and risk. The IGT was divided into five blocks of 20 trials; analysis showed that activity in the medial prefrontal cortex (mPFC) moves gradually from the dorsal to the ventral mPFC over the course of the IGT. These findings suggest that cognitive division of the mPFC, including the dorsal portion of the anterior cingulated cortex (ACC), plays a major role in ambiguous decision making and that the aspect of the IGT corresponding to risky decision making is associated with significant activity within the corticolimbic network strongly implicated in emotion and reinforcement. Our results also suggest that decisions made under ambiguity and decisions made under risk situations can be further divided into sub-phases based on the neural network involved.

• Journal of the Korean Magnetics Society
• /
• v.10 no.3
• /
• pp.106-111
• /
• 2000

The magnetic thin films can be prepared without vacuum process and under the low temperature (<100 $^{\circ}C$) by ferrite plating. We have performed ferrite plating of M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$(x=0.00~0.08) films and N $i_{x}$Z $n_{0.22}$F $e_{*}$2.78-x/ $O_4$(x=0.00~0.15) films on cover glass at the substrate temperature 90 $^{\circ}C$. The crystal structure of the samples has been identified as a single phase of polycrystal spinel structure by x-ray diffraction technique. The lattice constant in the M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$films increases but in the N $i_{x}$Z $n_{0.22}$F $e_{*}$2.78-x/ $O_4$films decrease with the composition parameter, x. The saturation magnetization in the M $n_{x}$Z $n_{0.22}$F $e_{2.78-x}$ $O_4$films does not greatly change, in agreement with observations on bulk samples.k samples.k samples.

• Journal of the Korean Magnetics Society
• /
• v.7 no.6
• /
• pp.293-298
• /
• 1997

$Fe_5Si_Xb_{5-x}$ (x=0, 1, 2, 3) powders were prepared by mechanical alloying, and their phases and magnetic properties were investigated by using XRD, TEM, Mossbauer spectroscopy and VSM. Starting elements are incorporated into $\alpha$-Fe in the early stage of mechanical alloying, and the stable phases are formed as the milling proceeds. After the annealing at 80$0^{\circ}C$ for 2 hours, it is found that the FeB and $Fe_2B$ phases coexist for the $Fe_5B_5$(x=0) composition. By substituting Si for B, the formation of $Fe_2B$ phase is restricted and the $Fe_5SiB_2$, $Fe_2Si_{0.4}B_{0.6}$ and paramagnetic phase begin to appear. The FeB phase has wide range of hyperfine magnetic field because it is not fully crystallized on the annealing at 800 $^{\circ}C$. On the contrary, others have good crystalline phases and show well-defined hyperfine magnetic field. Magnetic saturation is highest for the $Fe_5B_5$ composition where the amount of the $Fe_2B$ phase in large.

• Journal of the Korean Magnetics Society
• /
• v.21 no.3
• /
• pp.88-92
• /
• 2011

We grew $Zn_{0.4}Fe_{2.6}O_4$ thin films using Pulsed Laser Deposition and studied their crystal structure and magnetical characteristics as a function of growth temperature ($T_g$). For the film with $T_g=300^{\circ}C$, X-ray reflections from ${\alpha}-Fe_2O_3$ and ZnO were observed. However, when $T_g$ was increased from 300 to $500^{\circ}C$, crystal structure of inverse spinel was stabilized with the crystal orientation of $Zn_{0.4}Fe_{2.6}O_4(111)/Al_2O_3(0001)$ without any detection of ${\alpha}-Fe_2O_3$ and ZnO phases. The surface morphology shows flattening behavior with increasing $T_g$ from 300 to $500^{\circ}C$. These observations indicate that Zn is substituted into tetrahedron A-site of the inverse-spinel $Fe_3O_4$. M-H curves exhibit clear ferromagnetism for the sample with $T_g=500^{\circ}C$ whereas no ferromagnetism is observed for the film with $T_g=300^{\circ}C$.

• Journal of the Korean Magnetics Society
• /
• v.20 no.5
• /
• pp.182-186
• /
• 2010

Effect of cobalt substitution on the sintering behavior and magnetic properties of a NiZnCu ferrite was studied. $Ni_{0.36-x}Co_xZn_{0.44}Cu_{0.22}Fe_{1.98}O_4(0{\leq}x{\leq}0.04)$ ferrite was fabricated by a solid stat reaction method. It was proposed and experimentally verified that $Co^{2+}$ substituted NiZnCu ferrite was effective on improving the quality factor and magnetic properties of NiZnCu ferrites for multilayer chip inductors. The ferrite was sintered without sintering aids, at $880{\sim}920^{\circ}C$, for 2 h and the initial permeability, quality factor, density, shrinkage, saturation magnetization, and coercivity were also measured. The quality factor (Q) was increased linearly up to x = 0.01 and decreased rapidly over x = 0.01. As the cobalt content increased, the initial permeability and density of the ferrites decreases. The initial permeability of toroidal sample for $Ni_{0.35}Co_{0.01}Zn_{0.44}Cu_{0.22}Fe_{1.98}O_4$ ferrites sintered at $900^{\circ}C$ was 130 at 1 MHz and quality factor was 230.

• Korean Journal of Materials Research
• /
• v.11 no.8
• /
• pp.685-689
• /
• 2001

We carried out these experiments to examine the effects of element substitution of Co and La-Co for Sr-ferrite. The calcined properties of Co and La-Co element substitution were examined, and also the sintered magnetic properties were measured with the stoichiometric condition. The magnetic properties of $(La-Co)_{0.3}-SrM$ composition are as follows; $(M_s)$: 71.08 emu/g, $iH_c$: 4.38 kOe and $B_r$ : 4.18 kG, $iH_ c$ :4.35 kOe, $BH_{max}$: 4.3 MGOe. The $BH_{max}$ value was increased up to 10 % compared with conventional values. Our results imply that the magnetic properties of Sr-ferrite can be improved by the substitution of those elements.

• Journal of the Korean Magnetics Society
• /
• v.13 no.3
• /
• pp.97-102
• /
• 2003

Synthetic ferrimagnetic layer (SyFL) with structure NiFe/Ru/NiFe which can be applied high density TMR device in free layer were prepared by an inductively coupled plasma (ICP) helicon-sputter. We proposed a model of predicting coercivity (H$\_$c/), spin-flopping field (H$\_$sf/), and saturation field (H$\_$s/) as a function of Ru thicknesses, from the equilibrium state of energies of Zeeman, exchange, and uniaxial anisotropy. We fabricated the samples of Ta(50 ${\AA}$)/NiFe(50${\AA}$)nu(4∼20${\AA}$)NiFe(30 ${\AA}$)/Ta(50${\AA}$), and measured the M-H loops with a superconduction quantum interference device (SQUID) applying the external field up to ${\pm}$ 15 kOe. The result was well agreed with the proposed model, and reveal K$\_$u = 1000 erg/㎤, J$\_$ex/ =0.7 erg/$\textrm{cm}^2$. We report that H$\_$c/ below 10 Oe is available, and R$\_$u/ thickness range should be in 4-10 ${\AA}$ for MRAM application. Our result implies that permalloy layers may lead to considerable magnetostriction effect in SyFL and intermixing in NiFe/Ru interfaces.

• Korean Journal of Materials Research
• /
• v.6 no.7
• /
• pp.733-741
• /
• 1996

In this study MeV Si self ion implantations were done to reveal the intrinsic behavior of defect formation by excluding the possibility of chemical interactions between substrate atoms and dopant ones. Self implantations were conducted using Tandem Accelerator with energy ranges from 1 to 3 MeV. Defect formation by high energy ion implantation has a significant characteristics in that the lattice damage is concentrated near Rp and isolated from the surface. In order to investigate the energy dependence on defect formation, implantation energies were varied from 1 to 3 MeV under a constant dose of $1{\times}10^{15}/cm^2$. RBS channe!ed spectra showed that the depth at which as-implanted damaged layer formed increases as energy increases and that near surface region maintains better crystallinity as energy increases. Cross sectional TEM results agree well with RBS ones. In a TEM image as-implanted damaged layer appears as a dark band, where secondary defects are formed upon annealing. In the case of 2 MeV $Si^+$ self implantation a critical dose for the secondary defect formation was found to be between $3{\times}10^{14}/cm^24$ and $5{\times}10^{14}/cm^2$. Upon annealing the upper layer of the dark band was removed while the bottom part of the dark band did not move. The observed defect behavior by TEM was interpreted by Monte Carlo computer simulations using TRIM-code. SIMS analyses indicated that the secondary defect formed after annealing gettered oxygen impurities existed in silicon.

• Journal of the Korean Magnetics Society
• /
• v.19 no.6
• /
• pp.209-215
• /
• 2009

M-type barium ferrite (BaFe12O19) powders were synthesized through the co-precipitation method. Starting material composition $Fe^{3+}:\;Ba^{2+}$ mole ratio was fixed as 8 and the relative amount of $Fe^{3+}$ and $Ba^{2+}$ was controlled. Structure and magnetic properties and powder morphology were investigated using XRD, SEM, VSM. Powder showing high coercivity and small magnetization was obtained at pH8 and $Fe_{3+}:\;Ba_{2+}$ of 12 : 1.5. Small magnetization value was originated from the existence of ${\alpha}-Fe_2O_3$. Single-phase Mtype barium ferrite were obtained regardless of the heat treatment condition and the amount of $Fe_{3+}\;and\;Ba_{2+}$ at pH$\approx$10. The largest value of magnetization (55.7 emu/g) under investigation were obtained when $Fe_{3+}:\;Ba_{2+}$ of 13.6 : 1.7 and furnace cooled powder in $O_2$. Particle size of powder was in the range of 50~200 nm.