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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.
Tho, P.T.,Dang, N.V.,Nghia, N.X.,Khiem, L.H.,Xuan, C.T.A.,Kim, H.S.,Lee, B.W. Elsevier 2018 The Journal of physics and chemistry of solids Vol.121 No.-
<P><B>Abstract</B></P> <P>In this investigation, we have studied the crystal structure and magnetic properties of Zn doped Bi0.84La0.16FeO3 (<I>x</I> = 0.02–0.1) ceramics at the morphotropic phase boundary of rhombohedral and orthorhombic phases. Rietveld refinement of the obtained XRD patterns and Raman spectroscopy confirm the presence of multiphases crystal structure of <I>R3c</I> rhombohedral and <I>Pbam</I> orthorhombic. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization and coercivity with dominating of orthorhombic phase. The isothermal structural transition from <I>R3c</I> to <I>Pbam</I> is caused for the decrease in magnetization and the increase in coercivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure of Bi<SUB>0.84</SUB>La<SUB>0.16</SUB>Fe<SUB>1-x</SUB>Zn<SUB>x</SUB>O<SUB>3</SUB> at the morphotropic phase boundary. </LI> <LI> The microstructure reveals the coexistence crystal phase and their phase boundary. </LI> <LI> The isothermal structural transition induces the change in magnetic properties. </LI> <LI> The vertical shift (exchange bias) is observed in compounds. </LI> </UL> </P>
Ferromagnetism and Spin-glass-like Behavior in (Nd0.65Y0.35)0.7Sr0.3MnO3
T. L. Phan,유성초,N. V. Dai,N. V. Khiem 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9
We have studied the ferromagnetism and spin-glass-like behavior in a polycrystalline perovskite of (Nd<SUB>0.65</SUB>Y<SUB>0.35</SUB>)<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3 </SUB>basing on investigations related to magnetization, magnetic AC susceptibility, and electron spin resonance (ESR). Magnetization measurements versus temperature reveal the spin-glass phase transition temperature <I>T</I><SUB>g</SUB> taking place at about 53 K. For the in-phase susceptibility, there is a frequency-dependent peak called the spin-freezing temperature <I>T<SUB>f.</SUB></I> The lowering of frequency to zero leads to <I>T<SUB>f</SUB></I> --> <I>T<SUB>g</SUB></I>. Dynamics of this process was analyzed by means of the slowing-down scaling law. the characteristic time <I>t</I><SUB>o</SUB> and critical exponent <I>zv</I> obtained by fitting the experimental <I>T<SUB>f</SUB></I> data are about 1.6×10<SUP>−15 </SUP>s and 10.12, respectively, different from those expected from the canonical spin-glass system with <I>t</I><SUB>o</SUB> = 10<SUP>-13</SUP> s and <I>zv</I> =10. The spin-glassy phenomenon is related to magnetic frustration phenomenon caused by strong competition between ferromagnetic and anti-ferromagnetic interactions, together with strongly magnetic disorder. Dynamics of magnetic interactions in (Nd<SUB>0.65</SUB>Y<SUB>0.35</SUB>)<SUB>0.7</SUB>Sr<SUB>0.3</SUB>MnO<SUB>3</SUB> has been also further studied by means of ESR.
Phan, T. L.,Nguyen, V. D.,Ho, T. A.,Khiem, N. V.,Thanh, T. D.,Phuc, N. X.,Thang, P. D.,Yu, S. C. IEEE 2014 IEEE transactions on magnetics Vol.50 No.6
<P>The magnetic properties of polycrystalline ceramic samples (Nd1-xYx)(0.7)Sr0.3MnO3 with x = 0.21 - 0.35 were studied by means of dc magnetization and ac susceptibility measurements. Experimental results reveal a strong decrease of the ferromagnetic (FM)-paramagnetic phase-transition temperature (T-C) from 97 to 65 K as increasing x from 0.21 to 0.35, respectively. There is magnetic inhomogeneity associated with short-range FM order. Particularly, the samples undergo a spin-glass (SG) phase transition at the so-called blocking temperature (T-B) below T-C, which shifts toward lower temperatures with increasing the applied field, Hex; T-B -> T-g (the SG phase-transition temperature) as H-ex -> 0. The existence of the SG behavior in these samples was also confirmed by frequency (f) dependences of the ac susceptibility. For the in-phase/real component, chi' (T), it shows a frequency-dependent peak at the SG freezing temperature (T-f); T-f -> T-g as f -> 0. Dynamics of this process were analyzed by means of the slowing down scaling law, tau/tau(0) proportional to (T-f/T-g - 1)(-zv), where tau(0) and zv are the characteristic time and critical exponent, respectively. Fitting the experimental T-f(f) data to the scaling law gave the results of zv = 10.1-12.3 and tau(0) = 10(-21)-10(-15)s. These values are different from those expected for canonical SG systems with zv = 10 and tau(0) = 10(-13)s, revealing the cluster-SG behavior of (Nd1-xYx)(0.7)Sr0.3MnO3 samples. Notably, the increase in Y content leads to the shift of tau(0) and zv values toward those of canonical SG systems, which is ascribed to an expansion of SG clusters.</P>
T. T. Doan Phan,T. T. M. Trinh,L. H. Khiem,M. V. Frontasyeva,N. H. Quyet 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.2
Atmospheric deposition of trace elements in three cities of Vietnam including Hue, Hoi An and Ho Chi Minh in Central and South of Vietnam has been studied in this work by moss technique. Thirty samples of the local moss Barbula indica were collected in these cities and the concentrations of thirty heavy elements were determined by neutron activation analysis at the reactor IBR-2 of the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research located in Dubna, Russia. Concentrations of thirty elements were determined in each sample. Factor analysis has been applied to the concentration data and five main factors, which characterized five possible sources of the air pollution affecting the investigated areas have been identified. The correspondence between the research results and the reality of the air pollution in the studied sites has proved high possibility of the method for studying air pollution in Vietnam.