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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.
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.
Ho, T. A.,Phan, M. H.,Phuc, N. X.,Lam, V. D.,Phan, T. L.,Yu, S. C. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.5
<P>The Ti-substitution influence on the magnetic and magnetocaloric properties of La0.7Ba0.3Mn1-x Ti (x) O-3 (x = 0.05 and 0.1) was investigated. Based on Banerjee's criteria and Franco's universal curves, we proved the existence of a second-order magnetic phase transition in the samples. Using the modified Arrott plot method, we determined the critical parameters T (C) a parts per thousand 245 K, beta = 0.374 +/- A 0.013, gamma = 1.228 +/- A 0.045, and delta = 4.26 +/- A 0.03 for x = 0.05, and T (C) a parts per thousand 169 K, beta = 0.339 +/- A 0.001, gamma = 1.307 +/- A 0.003, and delta = 4.78 +/- A 0.02 for x = 0.1. With these critical values, the predictable scaling behavior of the M(H) data above and below T (C) proves that the calculated exponents are unambiguous and intrinsic. The values beta = 0.374 for x = 0.05 and beta = 0.339 for x = 0.1 suggest that the magnetic phase transition of the samples falls into the three-dimensional (3D) Heisenberg and 3D Ising universality classes, respectively, corresponding to short-range ferromagnetic (FM) order due to FM clusters in a wide temperature range even above T (C), as confirmed by electron spin resonance studies. In reference to the magnetocaloric effect around T (C), the magnetic entropy change reaches maximum values (|Delta S-max|) of about 4 and 3 J kg(-1) K-1 for x = 0.05 and 0.1, respectively, for a magnetic field change 50 kOe. Magnetic field dependencies of |Delta S-max| obey a power function |Delta S-max(H)| ae H (n) , where exponent values n = 0.59 and 0.61 for x = 0.05 and 0.1, respectively, were determined from the relation n = 1 + (beta-1)/(beta + gamma). The difference between the experimental n values and the theoretical value n = 2/3 of the mean field model is due to the presence of short-range FM order in the samples.</P>
Tuning of the Curie Temperature in La1-xSrxMn1-yTiyO₃
N. X. Phuc,N. T. Hieu,N. T. H. Le,D. H. Manh,N. A. Tuan,L. V. Hong,L. T. C. Tuong 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
Magnetic nanoparticles of La₁-xSrxMn₁-yTiyO₃ were prepared by using a sol-gel method, followed by annealing at various elevated temperatures. We found that the Curie temperature of the manganite nanoparticles could easily be tuned (from TC ~ 90 ℃ down to ~20 ℃) by substitution of nonmagnetic Ti⁴+ ions (from y = 0 to 7 %) for Mn. A comparison showed that the titanium substitution approach had advantages such as the phase transition being sharper and the magnetization remaining higher than in the case of the earlier known way of TC reduction by decreasing the Sr content from the optimal value of x = 0.3. The new features seem to make La1..xSrxMn₁..yTiyO₃ nanoparticles promising for hyperthermia application. Magnetic nanoparticles of La₁-xSrxMn₁-yTiyO₃ were prepared by using a sol-gel method, followed by annealing at various elevated temperatures. We found that the Curie temperature of the manganite nanoparticles could easily be tuned (from TC ~ 90 ℃ down to ~20 ℃) by substitution of nonmagnetic Ti⁴+ ions (from y = 0 to 7 %) for Mn. A comparison showed that the titanium substitution approach had advantages such as the phase transition being sharper and the magnetization remaining higher than in the case of the earlier known way of TC reduction by decreasing the Sr content from the optimal value of x = 0.3. The new features seem to make La1..xSrxMn₁..yTiyO₃ nanoparticles promising for hyperthermia application.
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.