• 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 ${\alpha}-Fe_2O_3$, $MnCO_3$, $CrF_3$.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.287-292
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• 2006

Al substituted $CoAl_{0.5}Fe_{1.5}O_{4}$ has been studied with x-ray and neutron diffraction, $M\"{o}ssbauer$ spectroscopy and magnetization measurements. $CoAl_{0.5}Fe_{1.5}O_{4}$ revealed a cubic spinel structure of ferrinmagnetic long range ordering at room temperature, with magnetic moments of $Fe^{3+}(A)(-2.29{\mu}_{B}),\;Fe^{3+}(B)(3.81\;{\mu}_{B}),\;Co^{2+}(B)(2.66{\mu}_{B})$, respectively. The temperature dependence of the magnetic hyperfine field in $^{57}Fe$ nuclei at the tetrahedral (A) and octahedral (B) sites was analyzed based on the $N\'{e}el$ theory of magnetism. In the sample of $CoAl_{0.5}Fe_{1.5}O_{4}$, the interaction A-B interaction and intrasublattice A-A superexchange interaction were antiferromagnetic with strengths of $J_{A-B}=-19.3{\pm}0.2k_{B}\;and\;J_{A-A}=-21.6{\pm}0.2k_{B}$, respectively, while the intrasublattice B-B superexchange interaction was found to be ferromagnetic with a strength of $J_{B-B}=3.8{\pm}0.2k_{B}$.

• Journal of the Korean Magnetics Society
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• v.3 no.3
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• pp.173-178
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• 1993

We have calculated the reduced spontaneous magnetization in different environments and average value as func¬tion of reduced temperature of the magnetic ions(Fe) for A(tetrahedral) and B(octahedral) sites in spinel ferrites $AB_{2}O_{4}$ using A-O-B superexchange interaction. The reduced spontaneous magnetization and average value by A-O-B superexchange interaction are compared with that by A-B direct interaction. To contrast A-O-B superexchange interaction with A-B direct interaction, $M\"{o}ssbauer$ spectra from previous two interactions are obtained.

• Journal of the Korean Magnetics Society
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• v.21 no.1
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• pp.1-4
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• 2011

We have studied magnetic structure and magnetic anisotropy energy of cubic transition metal mono-oxide cluster FeO and MnO using OpenMX method based on density functional method. The calculation results show that the antiferromagnetic spin arrangement has the lowest energy for FeO and MnO due to the superexchange interactions. The magnetic anisotropy is only found for antiferromagnetically ordered FeO cluster, since occupied electron of 3d down-spin level induces the spin-orbit couplings with <111> directed angular momentum.

• Journal of the Korean Magnetics Society
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• v.22 no.4
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• pp.121-124
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• 2012

We have studied electronic and magnetic structure of cubane-type Mn4 cluster using OpenMX method based on density functional method. The calculated density of states shows that the octahedron of O atoms split $e_g$ and $t_{2g}$ energy levels like bulk MnO with cubic structure. Total energy with antiferromagnetic spin configuration is lower than those of other spin configurations because of super exchange interaction. Calculated exchange interaction J between Mn atoms with anti-parallel spin is larger than between Mn atoms with parallel spin.

• Journal of the Korean Magnetics Society
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• v.5 no.3
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• pp.171-174
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• 1995

We have studied the paramagnetic $CuF_{2}$ using the techniques of pulsed nuclear magnetic resonance(NMR). The powder sample revealed two well-separated lines from the distinct $^{19}F$ sites at room temperature and at 77 K. The distinct frequency shifts of the two lines appear to arise from electron transfers. Furthermore, the two sites have very short spin-lattice relaxation times ($T_{1}$). The frequency-shifted site has the shorter $T_{1}$ than the unshifted one, reflecting the difference of the electron environments of the two sites.

• Journal of the Korean Magnetics Society
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• v.23 no.2
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• pp.43-48
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• 2013

The Jahn-Teller distortion of chalcogenide $Fe_{0.9}M_{0.1}Cr_2S_4$ (M=Co, Ni, Zn) have been investigated by M$\ddot{o}$ssbauer spectroscopy. The crystal structures of $Fe_{0.9}M_{0.1}Cr_2S_4$ (M=Co, Ni, Zn) are cubic spinel at room temperature. Magnetoresistance measurements indicate these system is conducting-semiconducting transistion around $T_C$. Below $T_C$, the asymmetric line broadening is observed and considered to be dynamic Jahn-Teller distortion. Isomer shift value of the samples at room temperature was about 0.5 mm/s, which means that charge state of Fe ions is ferrous in character. The Ni substitutions for Fe occur to increase the Jahn-Teller relaxation. CMR properties could be explained with magnetic polaron due to Jahn-Teller effect, which is different from both the double exchange interactions of manganite system and the triple exchange interactions of chalcogenide $Cu_xFe_{1-x}Cr_2S_4$.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.46-50
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• 2004

Compounds of $Y_{3-x}Ce_{x}Fe{5}O_{12}$(x=0.0, 0.1, 0.2, and 0.3) were prepared using the sol-gel method. The XRD measurements show that these samples have only a single phase of the garnet structure regardless of the amount of Ce substitution. The lattice constants of x = 0.0 and x = 0.3 were found to be a$_0$ = 12.3758 ${\pm}$0.0005 ${\AA}$ and 12.4062 ${\pm}$0.0005 ${\AA}$, respectively. The lattice constant increases linearly with increasing Ce concentration. The saturation magnetization was not changed flirty, with increasing Ce concentration, but coercivity decreased form 18.3 Oe to 5.8 Oe as x increased form x = 0.0 to x = 0.1. Mossbauer spectra of $Y_{3-x}Ce_{x}Fe{5}O_{12}$ were measured at various absorber temperatures from 13 K to Neel temperature. The Mossbauer spectra were fitted by least-squares technique with two subpatterns of Fe sites in the structure and corresponding to the 16a and 24d site. The temperature dependence of the magnetic hyperfine field in $^{57}$/Fe nuclei at the tetrahedral 240 and octahedral 16a sites were analyzed based on the Neel theory of ferrirnagnetism. The result of the Debye temperatures indicated that the inter-atomic binding force for the 24d site was larger than that for the 16a site.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.386-392
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• 2021

Multiferroics exhibiting the coexistence and a possible coupling of ferromagnetic and ferroelectric order are attracting widespread interest in terms of academic interests and possible applications. However, room-temperature single-phase multiferroics with soft ferromagnetic and displacive ferroelectric properties are still rare owing to the contradiction in the origin of ferromagnetism and ferroelectricity. In this study, we demonstrated that sizable ferromagnetic properties are induced in the ferroelectric bismuth ferrite-barium titanate system simply by introducing Co ions into the A-site. It is noted that all modified compositions exhibit well-saturated magnetic hysteresis loops at room temperature. Especially, 70Bi_0.95Co_0.05FeO₃-30Ba_0.95Co_0.05TiO₃ manifests noticeable ferroelectric and ferromagnetic properties; the spontaneous polarization and the saturation magnetization are 42 µC/cm² and 3.6 emu/g, respectively. We expect that our methodology will be widely used in the development of perovskite-structured multiferroic oxides.

• Korean Journal of Materials Research
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• v.11 no.1
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• pp.3-7
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• 2001

$M\"{o}ssbauer$ spectra of the $Ni_{1+x}Ti_xFe_{2-2x}O_4$ systems ($0{\leqq}x{\leqq}0.7$), which appear as single phase spinel structure, were examined at RT. The $M\"{o}ssbauer$ spectra reveal two sextet for $0{\leqq}x{\leqq}0.3$, two sextet and a doublet for $0.4{\leqq}x{\leqq}0.6$, and a doublet for x=0.7 As x increases, the area ratio of B-site and A-site($A_B/A_A$) of the sextet decreases, and the area ratio of the doublet and the total areas($A_{doublet}/A_{tot.}$) increases. The isomer shift(I.S.) of A-site slightly increases and magnetic hyperfine fields($H_{hf}$) of two sites decrease as the increasing x. From these results, we have obtained the cation distributions of the samples and concluded that the increasing x leads to the decrease of covalency of $Fe^{3+}-O^{2-}$ bond in A-sites and A-B superexchange interactions.eractions.