• Journal of Magnetics
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• v.11 no.4
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• pp.164-166
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• 2006

We have investigated the dielectric and magnetic properties of ferroelectric-antiferromagnetic $BaTiO_{3}-LaMnO_{3}$ composite with changing relative mole percents. Due to high sintering temperature, i.e. $1150^{\circ}C$, the Ba ion in $BaTiO_{3}$ seems to diffuse into $LaMnO_{3}$; resulting in $BaTiO_{3}-(La,Ba)MnO_{3}$ ferroelectric-ferromagnetic composite. At room temperature, $0.9BaTiO_{3}-0.1LaMnO_{3}$ composite exhibits considerable magnetization (${\sim}0.7\;emu/g\;at\;2000\;Oe$) and low coercive field (${\sim}5\;Oe$). Also it exhibits high dielectric constant (${\sim}560$) and low loss (${\sim}0.08$) at 10 kHz. This result may imply that $BaTiO_{3}-LaMnO_{3}$ could be suitable for a low leakage multiferroic composite.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.119-123
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• 2016

We have studied electronic and magnetic structure of cubane-type Cu magnetic molecule using density functional method. The calculated density of states show that Cu has 3d $x^2-y^2$ hole orbital because of short distances between Cu atom and in-plane 4 ligand atoms. The calculated total energy with in-plane antiferromagnetic spin configuration is lower than those of ferromagnetic configurations. The calculated exchange interaction J between in-plane Cu atoms is much larger than those between out-plane Cu atoms, since the $x^2-y^2$ hole orbital ordering of Cu 3d orbitals induces strong super-exchange interaction between in-plane Cu atoms.

• Proceedings of the Korean Magnestics Society Conference
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• 2011.06a
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• pp.3-3
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• 2011

Since the first discovery of exchange anisotropy on Co/CoO system[1], there have been numerous studies to explore the physical origin of exchange-biased system[2,3]. In this presentation, we report that how the polarized neutron reflectomery can be applied to study the magnetization reversal behavior of the exchange biased system. As an example, the detailed magnetization reversal mechanism of the exchange-biased Py(30 nm)/FeMn (0, 15, 30 nm)/CoFe(30 nm) trilayers was studied and found that the 15 nm antiferromagnetic FeMn layer mediates the magnetization reversal behaviors of both Py and CoFe layers through interlayer exchange bias coupling. We also update the current activities in polarized neutron reflectometer in HANARO.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.215-220
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• 2007

The superexchange interaction is introduced to explain antiferromagnetic ordering in transition metal compounds such as MnO and $MnF_2$. The anisotropic superexchange (Dzyaloshinskii-Moriya: DM) interaction can be derived by incorporating the spin-orbit interaction into the superexchange interaction. The anisotropic superexchange DM can account for the weak ferromagnetism observed in transition metal compounds such as ${\alpha}-Fe_2O_3$, $MnCO_3$, $CrF_3$.

• Proceedings of the Korean Magnestics Society Conference
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• 2015.05a
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• pp.161-163
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• 2015

The micro device, coil, and channel for the biosensor integrated with the GMR-SV device based on the antiferromagnetic IrMn layer was fabricated by the light lithography process. When RBCs coupled with several magnetic beads with a diameter of $1{\mu}m$ passed on the micro channel, the movement of RBC + ${\mu}Beads$ is controlled by the electrical AC input signal. The RBC + ${\mu}Beads$ having a micro-magnetic field captured above the GMR-SV device is changed as the output signals for detection status. From these results, the GMR-SV device having the width magnitude of a few micron size can be applied as the biosensor for the analysis of a new magnetic property as the membrane's deformation of RBC coupled to magnetic beads.

• Bulletin of the Korean Chemical Society
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• v.35 no.11
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• pp.3244-3248
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• 2014

Two ethylenediamine cobalt(II) oxalate complexes Co(ox)(en), 1 and $Co(ox)(en){\cdot}2H_2O$, 2 have been hydrothermally synthesized and characterized by single crystal X-ray diffraction, IR spectrum, TG analysis, and magnetic measurements. In 1, Co atoms are coordinated by two bis-bidentate oxalate ions in transconfiguration to form Co(ox) chains, which are further bridged by ethylenediamine molecules to produce 2D grid layers, Co(ox)(en). In 2, Co atoms are coordinated by bridging oxalate ions in cis-configuration to form Co(ox) chains, and the additional chelation of ethylenediamine to Co atoms completes 1D zigzag chain, Co(en)(ox). Two lattice water molecules stabilize the chains through hydrogen bonding. Magnetic susceptibility measurements indicate that both complexes exhibit weak antiferromagnetic coupling between cobalt(II) ions with the susceptibility maxima at 23 K for 1 and 20 K for 2, respectively. In 1 and 2, the oxalate ligands afford a much shorter and more effective pathway for the magnetic interaction between cobalt ions compared to the ethylenediamine ligands, so the magnetic behaviors of both complexes could be well described with 1D infinite magnetic chain model.

• Bulletin of the Korean Chemical Society
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• v.29 no.1
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• pp.122-126
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• 2008

The magnetic properties of the organic/inorganic hybrid copper-methylenediphosphonate, Cu2(O3PCH2PO3) were examined by performing the spin dimer analysis based on the extended Hckel tight binding method. In Cu2(O3PCH2PO3) the CuO3 chains made up of edge-sharing CuO5 square pyramidal units are inter-linked by O-P-O bridges. The Cu-O-Cu superexchange interactions of the CuO3 chains are negligibly weak compared with the Cu-O…O-Cu super-superexchange interactions that occur between the CuO3 chains. The spin exchange interactions of Cu2(O3PCH2PO3) are dominated by three super-superexchange interactions, which leads to a three-dimensional antiferromagnetic spin lattice. The strongest spin exchange interactions form isolated spin dimers, which suggests that, to a first approximation, the magnetic properties can be described in terms of an isolated spin dimer model.

• Korean Journal of Materials Research
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• v.13 no.7
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• pp.447-452
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• 2003

Effects of annealing and thickness of Co layer in Co/IrMn bilayers on the magnetic properties have been investigated. The highest interfacial exchange coupling energy($J_{K}$ = 0.12 erg/$\textrm{cm}^2$) was obtained for 10 nm Co layer thickness. Exchange bias field is inversely proportional to the magnetization, the thickness of the pinned layer, and the grain size of antiferromagnetic layer. Also it is related to the interfacial exchange energy difference, which is expected to depend on the surface roughness. These results almost agree with the random-field model of exchange anisotropy proposed by Malozemoff. Exchange bias field decreased slowly with increasing annealing temperature up to X$300^{\circ}C$. However, exchange bias field increased above $300^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.231-232
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• 2008

The coupling between electric, magnetic, and structural order parameters results in the so-called multiferroics, which possess ferroelectricity, ferromagnetism, and/or ferroelasticity. The simultaneous ferroelectricity and ferromagnetism (magnetoelectricity) allow potential applications in information storage, spintronics, and in magnetic or electric field sensors. Perovskite compound $BiFeO_3$ (BFO) is antiferromagnetic below Neel temperature of 647K and ferroelectric with a high Curie temperature of 1043K. It exhibits weak magnetism at room temperature(RT) due to the residual moment from a canted spin structure. It is likely that non-stoichiometry and second-phase formation are the factors which cause leakage in BFO. It has been suggested that oxygen non-stoichiometry leads to valence fluctuations of Fe ions in BFO, resulting in high conductivity. To reduce the large leakage current of BFO, one attempt is fabricating donor doped BFO compounds and thin films. We report here the successful fabrication of the Nd, Ti co-doped $BiFeO_3$ ceramics and thin films by pulsed laser deposition technique.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.1965-1969
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• 2014

A new tetranuclear Mn(III) complex $[Mn^{III}{_4}(sae)_4({\mu}_3-O)({\mu}_{1,1}-N_3)(OH)(H_2O)_2]{\cdot}H_2O$ (1) ($H_2sae$ = 2-salicylideneamino-1-ethanol) has been synthesized by the reaction of $MnCl_2{\cdot}4H_2O$, $H_2sae$ and sodium azide in the mixed solvent of methanol, acetonitrile and water. The X-ray diffraction analysis shows that the four Mn(III) ions in complex 1 have a unique adamantine arrangement, whereas the coordination environment of each Mn(III) ions is different. Magnetic studies indicate that complex 1 manifests antiferromagnetic behaviors. The magnetic susceptibilities of complex 1 have been fitted by two magnetic models based on the suitable analysis of its magnetic structural topology.