• Journal of Magnetics
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• v.18 no.1
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• pp.34-38
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• 2013

This paper studies the effects of the Mn-site substitution by nickel on the magnetic properties and the magnetocaloric properties of $La_{0.7}Ca_{0.3}Mn_{1-x}Ni_xO_3$ (x = 0, 0.05 and 0.1). The orthorhombic crystal structures of the samples are confirmed by the room temperature X-ray diffraction. The dependence of the Curie temperature ($T_C$) and the magnetic entropy change (${\Delta}S_M$) on the Ni doping content was investigated. The samples with x = 0 had the first order phase transition, while the samples with x = 0.05 and 0.1 had the second order phase transition. As the concentration of Ni increased, the maximum entropy change (${\mid}{\Delta}S_M{\mid}_{max}$) decreased gradually, from 2.78 $J{\cdot}kg^{-1}{\cdot}K^{-1}$ (x = 0) to 1.02 $J{\cdot}kg^{-1}{\cdot}K^{-1}$ (x = 0.1), in a magnetic field change of 15 kOe. The measured value of $T_C$ was 185 K, 150 K and 145 K for x = 0, 0.05 and 0.1, respectively. The phase transition temperatures became wider as x increased. It indicates that the Mn-site substitution by Ni may be used to tailor the Curie temperature in $La_{0.7}Ca_{0.3}Mn_{1-x}Ni_xO_3$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.2
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• pp.71-78
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• 1991

The congruent composition of $LiNbO_3$ was determined by measuring Curie temperature($T_c$) of crystals and residual melt grown from the range 48.45 to 48.60mole%$Li_2O$ melts. The $T_c$ of $LiNbO_3$ varied with compositon largely. The variation of $T_c$ with composition was found to follow $T_c=l0.4184c^2-962. 996C + 23342$, where C is mole % LizO. DSC-1500 was used to measure $T_c$. Distribution coefficients for $LiNbO_3$$ LiNbO_3$ contains 48.52mole$Li_2O$ and has a measured Tc of $1145{\pm}^{\circ}C$

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.10
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• pp.615-619
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• 2015

In this study, in order to develop the composition ceramics with the excellent electrocaloric properties, 8/65/35 PLZT ceramics were fabricated by the conventional solid-state method with the addition of $Bi_2O_3$, CuO, $Li_2CO_3$ and the variation of sintering temperature from $930^{\circ}C$ to $990^{\circ}C$. The XRD pattern of all specimens indicated general perovskite structure and the rhombohedral phase were observed. Curie temperature ($T_c$) of all specimens was observed in the vicinity of about $190^{\circ}C$. Density, coercive field and remnant polarization of the specimen sintered at $950^{\circ}C$ was $7.55g/cm^3$, 8.895 kV/cm, $11.22{\mu}C/cm^2$, respectively. EC effect of PLZT ceramics was measured by indirect method and the temperature change ${\Delta}T$ due to the electrocaloric effect was calculated by Maxwell's relations. ${\Delta}T$ of ceramic sintered at $950^{\circ}C$ was $0.21^{\circ}C$ under application of 40 kV/cm at $190^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.336-336
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• 2008

A positive temperature coefficient of electrical resistivity (PTCR) was investigated in a ferroelectric lead-free perovskite-type compound $(Bi_{0.5}K_{0.5})TiO_3$ within $BaTiO_3$-based solid solution ceramics. The electrical properties and the microstructure of (1-x) $BaTiO_3$ - x $(Bi_{0.5}K_{0.5})TiO_3$ (BBKT) ceramics made using a conventional mixed and have been synthesized by an ordinary sintering technique. The Curie temperature was obviously increased with increasing of $(Bi_{0.5}K_{0.5})TiO_3$ content. The BKT ceramics (x=0.05) sintered at $1400^{\circ}C$ for 4h display low resistivity values of $10^1-10^2$ ohm cm at room temperature, PTCR effect(jump) of 1.05*$10^3$, and the Curie temperature of $T_c=141^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.7 no.2
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• pp.90-96
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• 1997

We have studied crystallographic and magnetic properties of $NdFe_{10.7}Ti_ {1.2}Mo_{0.1}$ by Mossbauer spectroscopy, X-ray diffraction and vibrating sample magnetometer (VSM). The alloys were prepared by arc-melting under an argon atmosphere. The $NdFe_{10.7}Ti_{1.2}Mo_{0.1}$ has pure a single phase, whereas $NdFe_{10.7}Ti_{1.3}$ contains some $\alpha$-Fe, conformed with X-ray diffractometry and Mossbauer measurements. The $NdFe_{10.7}Ti_ {1.2}Mo_{0.1}$ has a $ThMn_{12}-type$ tetragonal structure with $a_0=8.637{\AA}$ and $c_0=4.807{\AA}$. The Curie temperature ($T_c$) is 600 K from the result of Mossbauer measurement performed at various temperatures ranging from 13 to 800 K. Each spectrum of below $T_c$ is fitted with five subspectra of Fe sites in the structure ($8i_1, 8i_2, 8j_2, 8j_1, 8f$). The area fractions of the subspectra at room temperature are 12.3%, 14.0%, 21.0% 11.8%, 40.9%, respectively. Magnetic hyperfine fields for the Fe sites decrease in the order, $H_{hf}(8i)>H_{hf}(8j)>H_{hf}(8f)$. The abrupt changes in the magnetic hyperfine field, an magnetic moment observed at about 160 K in $NdFe_ {10.7} Ti_{1.2}Mo_{0.1}$ are attributed to spin reorientations. The average hyperfine field of the $NdFe_{10.7}Ti_{1.2}Mo_{0.1}$ shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.34(T/T_C)^{3/2}-0.14(T/T_C)^{5/2}$ for $T/T_c<0.7$, indicative of spin wave excitation. The Debye temperatures of $NdFe_{10.7}Ti_{1.2}Mo_{0.1}$ is found to be Θ=340$\pm$5 K.

• Journal of Magnetics
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• v.18 no.4
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• pp.386-390
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• 2013

This paper studies the effects of A-site substitution by barium on the magnetic and magnetocaloric properties of $Pr_{0.5}Sr_{0.5-x}Ba_{x}MnO_{3}$ (x = 0, 0.04, 0.08 and 0.1). The tetragonal crystal structures of the samples are confirmed by room temperature X-ray diffraction. The dependence of the Curie temperature ($T_C$) and the magnetic entropy change (${\Delta}S_M$) on the Ba doping content has been investigated. The samples of all doping contents undergo the second order phase transition. As the concentration of Ba increased, the maximum entropy change ($|{\Delta}S_M|_{max}$) increased gradually, from 1.15 J $kg^{-1}$ $K^{-1}$ (x = 0) to 1.36 J $kg^{-1}$ $K^{-1}$ (x = 0.1), in a magnetic field change of 1.5 T. The measured value of $T_C$ is 265 K, 275 K, 260 K and 250 K for x = 0, 0.04, 0.08 and 0.1, respectively. If combining these samples for magnetic refrigeration, the temperature range of ~220 K and 290 K, where |${\Delta}S_M$|max is stable at ~1.27 J $kg^{-1}$ $K^{-1}$ and RCP = 88.9 $J{\cdot}kg^{-1}$ for ${\Delta}H$ = 1.5 T. $Pr_{0.5}Sr_{0.5-x}Ba_{x}MnO_{3}$ compounds, are expected to be suitable for magnetic-refrigeration application due to these magnetic properties.

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.485-487
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• 1993

The critical behavior of the classical D-dimensional spin model (D${\ge}$2), which is intermediate model that link up the Ising (D = 1) and the spherical model (D = ${\infty}$), is studied for the case of constant coupling interaction independent of the spin-spin distance (Curie-Weiss model). Analytical results show that the critical behavior of the present model is in quantitative agreement with the prediction of the phenomenological mean-field theory independent of D. Critical temperature is calculated to be T$_c$=k/JD. This gives a quantitative explanation of the relationship between the spin degree of freedom and the critical temperature.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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• pp.638-644
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• 2008

The effects of $Nb_2O_5$ and $MnO_2$ on the positive temperature coefficient of resistivity (PTCR) behavior of lead-free $Ba_{0.99}(Bi_{1/2}Na_{1/2})_{0.01}TiO_3$ (BaBiNT) ceramics were investigated in order to fabricate a PTC thermistor available at high temperature of > $120^{\circ}C$. In particular, 0.05 mol% $Nb_2O_5$ added BaBiNT ceramic, which has significantly increased Curie temperature (Tc) of $160^{\circ}C$, showed good PTCR behavior; low resistivity at room temperature $(\rho_r)$ of $80.1{\Omega}{\cdot}cm$, a high $\rho_{max}/\rho_{min}$ ratio of $5.65{\times}10^3$ and a large resistivity temperature factor (a) of 18.5%/$^{\circ}C$. Furthermore, the improved $\rho_{max}/\rho_{min}$ of $6.48{\times}10^4$ and a of 25.4%/$^{\circ}C$ along with higher $T_c$ of $167^{\circ}C$ despite slightly increased $\rho_r$ of $569{\Omega}{\cdot}cm$, could be obtained for the BaBiNT + 0.05 mol% $Nb_2O_5$ + 0.02 wt% $MnO_2$ ceramic cooled down at a rate of $200^{\circ}C/h$.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.1-7
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• 1992

Deuterium was injected into melt-spun ribbons of ${\alpha}-Fe_{90}Zr_{10}$ using the electrolytic hydrogenation method, and the magnetic properties of these ${\alpha}-D_{x}Fe_{90}Zr_{10}$ ribbons were studied. By comparing these results with those of ${\alpha}-H_{x}Fe_{91}Zr_{9}$, the effects of phonons to magnetic properties were investigated. The Curie temperature $T_{c}$, and the spontaneous magnetizations of the $D_{47}Fe_{90}Zr_{10}$ and the $Fe_{90}Zr_{10}$ were studied using the Mbssbauer spectroscopy. From these investigations, it was found that the Curie temperature of $D_{x}Fe_{90}Zr_{10}$ was 75K higher than that of $Fe_{90}Zr_{10}$. It was believed that this indicated the importance of local deformation to the amorphous magnetism. Also by comparing the spontaneous magnetizations of $D_{47}Fe_{90}Zr_{10}$ with those of $Fe_{90}Zr_{10}$ as a function of temperature, it was found that the deuterium injection reduced the fluctuation of exchange integral.

• Korean Journal of Materials Research
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• v.26 no.1
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• pp.35-41
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• 2016

The electrical transport properties of $La_{0.5}Sr_{0.5}CrO_3$ below room temperatures were investigated by dielectric, dc resistivity, magnetic properties and thermoelectric power. Below $T_c$, $La_{0.5}Sr_{0.5}CrO_3$ contains a dielectric relaxation process in the tangent loss and electric modulus. The $La_{0.5}Sr_{0.5}CrO_3$ involves the transition from high temperature thermal activated conduction process to low temperature one. The transition temperature corresponds well to the Curie point. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The low temperature conduction and relaxation takes place in the ferromagnetic phase. The ferromagnetic state in $La_{0.5}Sr_{0.5}CrO_3$ indicates that the electron - magnon interaction occurs, and drives the carriers towards localization in tandem with the electron - lattice interaction even at temperature above the Curie temperature.