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Low-Field Magnetoresistance of La0:7Sr0:3MnO3 Thin Film Fabricated by Using Pulsed-Laser Deposition
이영백,N. V. Dai,N. C. Thuan,L. V. Hong,N. X. Phuc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
La0:7Sr0:3MnO3 thin films were grown on n-Si (100) substrates in a high vacuum by using pulsed-laser deposition. The magnetic and the transport properties were investigated. The results showed that large magnetoresistance (MR) effects were achieved near and far below the ferromagnetic transition temperature TC. At low temperatures, the MR(H) curves are divided into two parts. In the high-magnetic-field region, the MR varies linearly with H and the ∂MR/∂H value is nearly independent of temperature. At low magnetic fields, however, the MR changes nonlinearly with magnetic field and is strongly temperature-dependent. The low-field MR(H) can be well fitted by assuming it to be proportional to M;2 suggesting that the main mechanism for the low-field MR effect at low temperatures is attributed to the tunneling of spin-polarized electrons between ferromagnetic grains.
Critical Exponents for the Ferromagnetic-Paramagnetic Transition in La0.7Sr0.3Mn0.8Ti0.2O3
N. V. Khiem,L. V. Bau,P. T. Phong,L. V. Hong,N. V. Dai,D. N. H. Nam,N. X. Phuc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
La0:7Sr0:3Mn0:8Ti0:2O3 compounds were studied by using dc magnetization measurements. The magnetic data analyzed in the paramagnetic-ferromagnetic phase transition region by using the Arrott plot method gave values of TC ~ 150:1 K for the Curie temperature and β = 0:518, = 1:0083 and δ = 2:95 for the critical exponents. The values obtained for the critical exponents are close to those predicted by the mean-feld theory. La0:7Sr0:3Mn0:8Ti0:2O3 compounds were studied by using dc magnetization measurements. The magnetic data analyzed in the paramagnetic-ferromagnetic phase transition region by using the Arrott plot method gave values of TC ~ 150:1 K for the Curie temperature and β = 0:518, = 1:0083 and δ = 2:95 for the critical exponents. The values obtained for the critical exponents are close to those predicted by the mean-feld theory.
Magnetoresistive Properties of Co2MnSi Heusler Alloy Films
N. V. Dai,M. S. Seo,T. W. Eom,이성재,M. Jang,이영백 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
Co2MnSi thin films were prepared on SOI wafers by using Co/Mn metal deposition and rapid thermal annealing at 650 C for 5 min in a high vacuum. The magnetoresistance (MR) of the Co2MnSi thin films was investigated in the temperature range from 50 to 300 K, and the MR behavior changed as magnetic field was increased. The MR(H) curves was divided into two parts: In the high-magnetic-field region, the MR varied linearly with the magnetic field. At low magnetic fields, however, the MR changed nonlinearly with the magnetic field and was strongly temperature-dependent. This behavior is similar to the MR response of polycrystalline colossal magnetoresistive manganite. By using a phenomenological model to fit the experimental data, we found that at high fields, the MR was dominated by intragrain scattering due to spin fluctuations
Effects of Selective Dilution on the MagneticProperties of La0.7Sr0.3Mn1-xM'xO3 (M' = Al, Ti)
D. N. H. Nam,N. V. Dai,L. V. Hong,N. X. Phuc,L. V. Bau,P. Nordblad,R. S. Newrock 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
The magnetic lattice of mixed-valence Mn ions in La0:7Sr0:3MnO₃ is selectively diluted by partial substitution of Al or Ti for Mn. The ferromagnetic transition temperature Tc and the saturation magnetization Ms both decrease with substitution. By presenting the data in terms of selective dilution, Tc in the low-doping region is found to follow the relation Tc = Tc0(1..np), where Tc0 refers to the undiluted system and np is the dilution concentration dened as np = x=0:7 or np = x=0:3 for M0 = Al or Ti, respectively. The scaling behavior of Tc(np) can be analyzed in the framework of the molecular-field theory and the still valid when Mn is replaced by both Al and Ti. The results are discussed with respect to the contributions from ferromagnetic double exchange and other possible antiferromagnetic superexchange interactions coexisting in the material. The magnetic lattice of mixed-valence Mn ions in La0:7Sr0:3MnO₃ is selectively diluted by partial substitution of Al or Ti for Mn. The ferromagnetic transition temperature Tc and the saturation magnetization Ms both decrease with substitution. By presenting the data in terms of selective dilution, Tc in the low-doping region is found to follow the relation Tc = Tc0(1..np), where Tc0 refers to the undiluted system and np is the dilution concentration dened as np = x=0:7 or np = x=0:3 for M0 = Al or Ti, respectively. The scaling behavior of Tc(np) can be analyzed in the framework of the molecular-field theory and the still valid when Mn is replaced by both Al and Ti. The results are discussed with respect to the contributions from ferromagnetic double exchange and other possible antiferromagnetic superexchange interactions coexisting in the material.
Dai, Y.,Oyunbaatar, N.-E.,Lee, B.-K.,Kim, E.-S.,Lee, D.-W. Elsevier 2018 Sensors and actuators. B Chemical Vol.255 No.3
<P><B>Abstract</B></P> <P>In this paper, a spiral-shaped SU-8 cantilever with biocompatibility was proposed to monitor the changes of cardiac contraction in response to injection of drug in real time. The cantilever comprises a thick quadrate body and a filmy spiral cantilever with micro-grooves and gold patterns on the top of its surface. The longitudinally patterned micro-grooves facilitate the aligned growth of cardiomyocytes in order to increase the contraction force. In addition, the spiral shape increases the cantilever’s effective length and decreases its spring constant, which means its bending displacement can be increased for the same force as compared to that observed in a conventional rectangular cantilever. The bending displacement of the spiral SU-8 cantilever induced by the contraction of cardiomyocytes can be precisely measured at the nanoscale using a homemade laser-based measurement system. The displacement in the spiral SU-8 cantilever without micro-grooves was much greater than that in the case of traditional rectangular SU-8 cantilevers. The displacement produced by the spiral cantilever with grooves is 240% greater than that without grooves. Following preliminary experiments, cardiac drugs including Verapamil, Quinidine, Lidocaine, E-4031, and Bay K 8644 were used to evaluate their side effects on cardiomyocytes. Quantitative analysis of measurements shows that not only Verapamil and Quinidine but also Lidocaine and E-4031 treatment can decrease the cell beating frequency, and both the Verapamil and Lidocaine treatment can decrease the cell contraction force. Furthermore, Bay K 8644 assay results indicate that it can decrease the contraction force and increase the beating frequency of cardiomyocytes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Spiral cantilever integrated with micro-grooves is proposed for a real time monitoring of cardiac contractibility. </LI> <LI> Home-made measurement system is developed to precisely measure the contractibility of cardiomyocytes at the nanoscale. </LI> <LI> Five different kind of drugs have been employed for the preliminary study of drug-induced cardiac toxicity. </LI> <LI> Spiral cantilever arrays are expected to be applied as a new method to support for the drawbacks of conventional methods. </LI> </UL> </P>