• Journal of Magnetics
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• 제3권3호
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• pp.86-88
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• 1998

A portable RF HTS SQUID-based susceptometer was used for small size magnetized sample testing in weak DC (up to 200A/m) and AC (up to 4 A/m) magnetic fields. The system resolution for the magnetic moment is of the order of $1.6{\times}10^{-10} A.m^2$. The measured DC susceptibility of a tested sample agrees well with the value obtained by using a commercial liquid helium susceptometer.

• Bulletin of the Korean Chemical Society
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• 제30권5호
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• pp.1143-1146
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• 2009

[$Mn_{12}O_{12}(azo-L)_{16}(H_2O)_4$] (1), a new Mn12 single molecule magnet containing a photochromic azobenzene ligand, has been successfully synthesized by substitution of acetate ligand of Mn12 with 6-[4-{4-hexyloxyphenyl( azo)}-phenoxy]hexanoic-1-acid. The reversible photoisomerization of the azobenzene group was confirmed by UV-visible absorption spectroscopy. The temperature and field dependence of dc susceptibility and the temperature and the frequency dependence of ac susceptibility were measured for the cis and the trans isomer of 1. The magnetization value of the cis isomer in dc measurement is higher than that of the trans isomer. The cis isomer of 1 has a slower relaxation because cis-trans photoisomerization of the azobenzene group in peripheral ligands induces changes in its structure and dipole moment.

• 한국자기학회지
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• 제5권5호
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• pp.515-518
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• 1995

We have studied the magnetization in fields up to 1T at 5K, the saturation magnetization dependence on temperature and the temperature dependence of AC-susceptibility at very low fields (5mOe to 50mOe) of glassy $Fe_{91-x}Zr_{7}B_{2}Ni_{x}$ (x = 0, 5, 10, 15) alloys. The temperature dependence of the magnetization follows the predictions of spin wave excitations with long wavelengths. At zero Ni concentration there is a clear competition between ferromagnetic and antiferromagnetic interactions giving rise to spin-glass behaviour. The addition of Ni drastically modifies the magnetic properties: the antiferromagnetic exchange coupling is reduced and finally disappears, the spin wave stiffness increases from 39.5 to $87.3\;meV{\AA}^{2}$ and To increases from 230 K to 478 K. We develop a simple model to quantify the competing interactions and to relate the antiferromagnetically coupled Fe moments to the Ni concentration. We find that the initial susceptibility increases with increasing Ni content along with a decrease of the temperature dependence.

• KIEE International Transactions on Electrophysics and Applications
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• 제3C권6호
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• pp.211-215
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• 2003

Alternating current (AC) losses of two Bi-2223 ([Bi, Pb] : Sr : Ca : Cu :O = 2:2:2:3) tapes [one untwisted (Tape I, twist-pitch of $\infty$ mm) and the other with a twist-pitch of 8mm (Tape II) ] were measured and compared. These samples, produced by the powder-in-tube (PIT) method, are multi-filamentary and have a Ag/Au and Ag matrix, respectively. Susceptibility measurements were conducted while cooling in a magnetic field. Flux loss measurements were conducted as a function of ramping rate, frequency and field direction. The AC flux loss increases as the twist-pitch of the tapes decreased, in agreement with the Norris Equation.

• Journal of Magnetics
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• 제4권1호
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• pp.10-12
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• 1999

We report the salient features of the magnetic properties of amorphous$ Fe_{84-x}Nb_7B_{8+x}Cu_1$ (x=0, 1, 4) alloys. The study of dc-magnetization properties and the ac-susceptibility was carried out. The temperature dependence of the magnetization follows the predictions of spin wave excitations with long wavelengths. Especially, the addition of boron modifies the magnetic properties: the spin wave stiffness increases from 56.8 to 65.7 meV$\AA$2 and Curie temperature increases from 298 K to 352 K. This result indicates a magnetic hardening of the exchange interaction by higher exchange energy. Thus, the substitution of iron by boron favours the increase of magnetic order in this system.

• 한국자기학회지
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• 제5권5호
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• pp.745-748
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• 1995

Magnetic nanoparticles of iron and iron oxide have been prepared in a modified upward thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about $60\;{\AA}$. FTIR spectrum measurements are used to investigate the difference in oxidation level between nanoparticles prepared at different partial oxygen pressures. The complex magnetic behaviour of these particles was studied using DC- and AC-susceptibility measurements. All samples exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. The coercivity fields as well as the dependence of the blocking temperature on measuring frequency have been studied. magnetic anisotropy constants are found to be one order of magnitude higher than is known for the bulk values. The mean particle size estimated from the magnetic data is found to be in perfect agreement with the TEM observations.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.150-151
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• 2003

In the past years, a giant magnetoresistance (GMR) effect found in perovskite-like structured materials has attracted considerable attention among scientists and manufacturers, since, a practical point of view, the capacity of producing magnetic and sensing sensors. In a stream of this interest, further efforts to understand the underlying mechanism that leads to the GMR effect relative to the correlation between transport and magnetic properties, have been extensively devoted. In these cases, spin-glass-like behaviors are ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co$\^$3+/ (or Mn$\^$3+/) and Co$\^$4+/(or Mn$\^$4+/) and the antiferromagnetic one like spins. Noticeably, the distinction of spin-glass region from cluster-glass one, involved in the remarkable changes in transport and magnetic properties at a critical value of doping concentration, was observed. Magnetic anomalies in zero-field-cooled (ZFC) magnetization as well as ac magnetic susceptibility below Curie temperature T$\sub$c/ and the charge/orbital fluctuation were also realized. In this work, we present a study of magnetic properties of a deficient manganese perovskites system of La$\sub$0.6/Sr$\sub$x/MnTi$\sub$y/O$_3$, and particularly provide its new magnetic phase diagram.

• Korean Journal of Radiology
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• 제25권3호
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• pp.267-276
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• 2024

Objective: To evaluate the diagnostic performance of susceptibility map-weighted imaging (SMwI) taken in different acquisition planes for discriminating patients with neurodegenerative parkinsonism from those without. Materials and Methods: This retrospective, observational, single-institution study enrolled consecutive patients who visited movement disorder clinics and underwent brain MRI and ¹⁸F-FP-CIT PET between September 2021 and December 2021. SMwI images were acquired in both the oblique (perpendicular to the midbrain) and the anterior commissure-posterior commissure (AC-PC) planes. Hyperintensity in the substantia nigra was determined by two neuroradiologists. ¹⁸F-FP-CIT PET was used as the reference standard. Inter-rater agreement was assessed using Cohen;s kappa coefficient. The diagnostic performance of SMwI in the two planes was analyzed separately for the right and left substantia nigra. Multivariable logistic regression analysis with generalized estimating equations was applied to compare the diagnostic performance of the two planes. Results: In total, 194 patients were included, of whom 105 and 103 had positive results on ¹⁸F-FP-CIT PET in the left and right substantia nigra, respectively. Good inter-rater agreement in the oblique (κ = 0.772/0.658 for left/right) and AC-PC planes (0.730/0.741 for left/right) was confirmed. The pooled sensitivities for two readers were 86.4% (178/206, left) and 83.3% (175/210, right) in the oblique plane and 87.4% (180/206, left) and 87.6% (184/210, right) in the AC-PC plane. The pooled specificities for two readers were 83.5% (152/182, left) and 82.0% (146/178, right) in the oblique plane, and 83.5% (152/182, left) and 86.0% (153/178, right) in the AC-PC plane. There were no significant differences in the diagnostic performance between the two planes (P > 0.05). Conclusion: There are no significant difference in the diagnostic performance of SMwI performed in the oblique and AC-PC plane in discriminating patients with parkinsonism from those without. This finding affirms that each institution may choose the imaging plane for SMwI according to their clinical settings.

• 한국세라믹학회지
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• 제44권6호
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• pp.308-312
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• 2007

Ferroelectric, magnetic, and magnetoelectric effects for lanthanum modified $BiFeO_3-PbTiO_3$ ceramics have been investigated. The data show that magnetoelectric polarization coefficient, ${\alpha}_p$ is due to a linear coupling between polarization and magnetization, and that ${\alpha}_p$ is independent of dc magnetic bias and ac magnetic field. The values of ${\alpha}_p$ and magnetic induced susceptibility for lanthanum modified $BiFeO_3-PbTiO_3$ ceramics are much larger than those of single $BiFeO_3$ crystal. We believe that the magnetoelectric effect is significantly enhanced by breaking of the cycloidal spin state of a long-period spiral spin structure due to randomly distributed charged imperfections.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.663-665
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• 1992

The superconducting $YBa_2Cu_4O_8$ was synthesized in oxygen condition at 1 atm. The starting material with 1 : 2 : 4 composition was obtained by pyrolysis of EDTA complex, which was converted to 1-2-3 phase during densification, followed by the 1-2-4 phase recovery at $810^{\circ}C$ . The phase presents were identified by XRD, TG, DTA and AC magnetic susceptibility. Our data indicated that considerable amounts of 1-2-4 phase formed but with the 1 : 2 : 3 phase or possibly 2-4-7 as visible. As the P($O_2$) increased with temperature, impurity peak, CuO ($2{\Theta}$ = 38.8), gradually decrease, and we conclude that the 1-2-4 phase is predominant bulk superconductor under the high oxygen pressure.