Papers by Keyword: AC Susceptibility

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Authors: L. D'Amico, Franco D'Orazio, J.L. Dormann, Franco Lucari, E. Tronc
Authors: Ji Liang Wang, Cheng Qian, Li Yu, Da Wei Qi
Abstract: Pr0.5Ca0.5Mn0.99Al0.01O3 compound was prepared by standard solid state reaction to study its ac susceptibility at low temperatures. The X-ray powder diffraction patterns show that the compound is single-phase orthorhombic structure. The cusps of charge ordering and the long range AFM order of the “pseudo”-CE type are suppressed with Al dopping in Pr0.5Ca0.5MnO3 compound. ZFC and FC magnetization of this compound bifurcate at Tf. The behavior of ac susceptibility at low temperatures is investigated. The intensity of the real component ' at the freezing temperature Tf is suppressed with the increase of frequency. Tf is linear with the logarithm of the frequency. The normalized slope P = ΔTf/TfΔlog10ω, which is much lower than canonical insulating spin glass systems in which 0.06 ≤ P ≤ 0.08. The intensity of '' at Tf increases with the increase of frequency. The ground state of this sample is cluster glass.
Authors: Mohammad Hoseein Ehsani, Parviz Kameli, Mohammad Ebrahim Ghazi, Fereidon Saadat Razavi
Abstract: Nanoparticles of La0.6Sr0.4MnO3 (LSMO) with an equivalent average particle size of ~ 20nm were synthesized by nitrate-complex auto-ignition method. The structural and magnetic properties were investigated systematically. The X-Ray diffraction study coupled with the Rietveld refinement of XRD data showed that sample crystallize in a rhombohedral structure with space group of R-3C. The stretching and bending modes in Fourier transform infrared (FTIR) spectroscopy is observed which indicates the formation of the perovskite structure of LSMO. The nature of DC magnetization versus field M(H) plot for sample resembles qualitatively with ferromagnetic (FM) systems. The AC-susceptibility data obtained at different frequencies confirmed the presence of a frequencydependent freezing temperature around room temperature. Based on the interparticle interaction strength and phenomenological models (Neel-Brown, Vogel-Fulcher and Critical slowing down) the magnetic dynamic behavior of nanoparticles was characterized. By fitting the experimental data with mentioned models the possibility existence of superparamagnetic/spin glass states were considered. The obtained values from fitting performance showed that there is a strong interaction between magnetic nanoparticles of LSMO.
Authors: F.B. Mushenok, O.V. Koplak, R.B. Morgunov, S.L. Chernyshova
Abstract: In this paper the contributions of switching, slide, creep and Debye relaxation modes of the domain wall dynamics to the low-frequency magnetic properties of chiral and racemic [MnII(HL-pn)(H2O)][MnIII(CN)6]2H2O molecular ferrimagnets were distinguished.
Authors: S. Bikić, I. Gazdić, M. Tais, S. Sulejmanović, N. Bajrović, T. Mihač
Authors: Nidhi M. Astik, G.J. Baldha
Abstract: The mineral having chemical compositional formula MgAl2O4 is called “spinel”. The ferrites crystallize in spinel structure are known as spinel-ferrites or ferro-spinels. The spinel structure has an fcc cage of oxygen ions and the metallic cations are distributed among tetrahedral (A) and octahedral (B) interstitial voids (sites). A compound of Co0.85Ca0.15-yMgyFe2O4 (y=0.05, 0.10, 0.15) is synthesized in polycrystalline form, using the stoichiometric mixture of oxides with conventional standard ceramic technique and characterized by X-ray diffraction (XRD).The XRD analysis confirmed the presence of cubic structure. The intensity of each Bragg plane is sensitive to the distribution of cations in the interstitial voids of the spinel lattice. The computer program Powder X software for XRD analysis has been utilized for this purpose. The compositions of Co0.85Ca0.15-yMgyFe2O4 (y=0.05, 0.10, 0.15) ferrites have been prepared by standard ceramic method with double sintering at 950°C, 1100°C. In present study, we report the structural, electrical and magnetic properties of above said compound.
Authors: Gabriel A. López, P.H. Domingues, V. Barthem, J.L. Sánchez Ll.
Authors: V.A. Ryzhov, Vladimir P. Khavronin, Vladimir V. Deriglazov, Yakov M. Mukovskii, Vladimir I. Chichkov
Abstract: The data on transport and magnetic properties (ac linear and nonlinear (second and third orders) susceptibilities) are presented for La0.7Sr0.3MnO3 single crystal with metallic behavior in paramagnetic (PM) region and ferromagnetic (FM) metallic ground state. The FM clusters originate in the PM matrix of the compound below some temperature T* > 425 K, their nonlinear response being weakly T-dependent down to 367 K. This was attributed to clusters arising in the preferable sites formed by chemical inhomogeneities introduced by doping. On cooling below T# ≈ 366 K > TC ≈ 363.3 K, a fast growth of cluster response without the change of its parameters is observed that was attributed to the development of homogeneous nucleation of the FM clusters. The latter stage continues below TC and is accompanied by a crossover to the steeper decreasing of resistivity with cooling that suggests metallic properties of the clusters. The cluster nonlinear response masks completely that of matrix at T = 360.3 K < TC, where it is well described by the model of ensemble of magnetic single-domain nanoparticles in superparamagnetic regime based on the formalism involving Gilbert-Landau-Lifshits equation. Below TD = 359.6 K at the stage of domain formation, a weak interaction of matrix and cluster subsystems leads to their mutual ordering, which is accompanied by a sharp decrease of the nonlinear response to a weak ac field in small steady field H. The latter suggests an “antiferromagnetic” type of arrangement of these subsystems that provides decreasing the magnetostatic energy of the sample.
Authors: Bekir Özçelik, Nilay Kantarci, Onur Nane, M. Eyyüphan Yakinci
Abstract: Physical properties of the Sm0.2Gd0.8Ni4B compound have been investigated by means of the X-ray powder diffraction, DC and AC-susceptibility techniques. The compound studied crystallizes in CeCo4B type structure with P6/mmm space group. The unit-cell parameters a and c are determined as 5.01 and 6.95 Å, respectively, and the unit-cell volume V is calculated as 151.08 Å3. DC and AC magnetic measurements present the visible magnetic phase transition from paramagnetic to ferromagnetic, around definite transition temperature. The magnetic phase transition temperature of the compound is obtained from DC magnetization, AC-susceptibility and the well known Kouvel-Fisher method as 36.6, 35.7 and 35.2 K, respectively. The saturation magnetization (Ms) and the coercive fields (Hc) of the compound are found to be 3.7µB/f.u and 277 Oe, respectively, by using the hysteresis loops at 9.5 K. We have also investigated the non-linear AC-susceptibility of the compound, around its ferromagnetic transition temperature, as a function of temperature, frequency and amplitude of the AC-driving field. In order to explain the measured experimental results, we have used the theory developed for ferromagnetic, based upon the mean field model. The measurements exhibit both frequency and amplitude dependencies. Observed dependencies are compared with the existing theories of linear and nonlinear susceptibilities with reference to short- and long-range interactions. In Kouvel-Fisher method, one plots 1/χ1*(dχ-1/dT) against T, obtaining a straight line. The slope of this line gives the critical exponent γ, and it intersects the T axis at Tc. In order to obtain -1/dT and the best straight line, we used a two-point numerical differentiation program and linear regression method, respectively. The critical exponent γ of the sample is calculated to be 2.78 ± 0.05. The value of the critical exponent β, which is characteristic of static phase transition to a ferromagnetic state, is estimated as 2.41±0.3 from the slope of the line obtained the plot of the absolute third-harmonic values versus the reduced temperature on a log–log scale.
Authors: Yi Yun Yang
Abstract: The magnetization, ac susceptibility and magnetic relaxation of Nd0.90Sr0.10CoO3 polycrystalline sample were systematically investigated in this paper. The experimental studies of susceptibility and magnetic relaxation evidence the existence of a low-temperature spin-glass. A dynamic analysis of ac susceptibility implies a spin-glass transition temperature TSG =12.17 K and the dynamical exponent zv=8. Moreover, low-temperature zero-field cooling and field cooling magnetic relaxation show perfectly mirror symmetry, and field cooling processes relaxation obeys a stretched exponential form. Therefore, our study confirms that the phase separation in Nd0.90Sr0.10CoO3 originates from both the ferromagnetic clusters interaction and the spin glasslike phase at low temperature.
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