Papers by Keyword: Curie Temperature

Abstract: Six compositions: x = 0.0 to 0.5 of the spinel system Mn1.5(1-x)Ti0.5(1-x)Fe(1+ 1.5x) Li(0.5)x O4 are synthesized by ceramic method. The structural and magnetic properties are studied by means of X-ray diffraction, AC susceptibility, Magnetization and Mossbauer spectroscopy. The study reveals the significance of FeA-O-FeB magnetic linkages in evolution of long range magnetic ordering through rise in Curie temperature and growth of magnetic hyperfine field with increase in x.

Abstract: The gallium and indium double-modified bismuth scandate-lead titanate (1-x)Bi (In_0.20Ga_0.05Sc_0.75)O₃-xPbTiO₃ ((1-x)BIGS-xPT, x=0.55-0.70) ceramics were prepared by using conventional ceramic technique. (1-x)BIGS-xPT ceramics for near x=0.60 exhibits an evident enhancement in room temperature dielectric and piezoelectric properties, with dielectric constant ε, piezoelectric constant d₃₃, planar electromechanical coupling coefficient k_p and Curie temperature T_C of 1100, 295 pC/N, 0.43 and 435 °C, respectively. The T_C of (1-x)BIGS-xPT is in the range of 425-530 °C for the compositions investigated. The combination of high T_C and excellent piezoelectric activity suggest that the (1-x)BIGS-xPT ceramics are usable candidate materials for high temperature piezoelectric devices applications.

Abstract: Abstract. In this paper, we modelled the phase transition between ferromagnetic and paramagneticstates in ultrathin films of different crystal structure near the percolation transition. Properties of ultrathinfilms have been studied within the framework of Ising model and the method of random-fieldinteraction. It is shown that the critical concentration of such phase transition depends on the symmetryof crystal lattice of the material. The increase in the film thickness leads to a decrease of the criticalconcentration up to a value of the percolation threshold of a massive sample of the correspondingcrystal structure.

Abstract: The algorithm for fast evaluation of the hysteresis loops of uniaxial or textured ferroelectric microcrystal or grains with long-range interactions is developed. Two types of ceramic microstructures are considered: 1. Random ceramics with complete isotropic distribution function of the crystallographic orientations of grains; and 2. Textured ceramics with anisotropic distribution function of the crystallographic orientations of grains. The qualitative analysis of the hysteretic behavior in terms of the grain distribution function is successfully demonstrated. Comparison of the calculated results with experimental data for Pb (Mg_1/3Nb_2/3)O₃ PbTiO₃ ceramics is presented.

Abstract: The structure transition and electrocaloric effect in PbZr_1-xTi_xO₃ with x=0.5 and 0.6 were MV/m can make the structural transition be a continuous one. In addition, when x =0.5 and 0.6 at the zero field, the first order structural transition occurs at T₀=665 and 691 K, respectively. The first order structural transition comes to the second one upon the strong electric field, which leads to lower the change of specific hea. The structural transition temperature is shifted at high temperature with increasing electric field. The maximum electrocaloric effect is present at about 200 K above their corresponding Curie temperatures.

Abstract: Ce_1-xDy_xFe_1.9(x = 0, 0.02, 0.05, 0.1) alloys were prepared successfully by means of arc-melting and the following homogenization. XRD patterns show all alloys are indexed as MgCu₂-type C15 cubic Laves phase structure. With the Dy substitution of Ce, the Curie temperatures from ferro-to para-magnetism become gradually enlarged. The values of for a magnetic-field change from 0-5 T at 234, 246, 268, 303 K are 31.7, 26.4, 21.8, and 17.2 J kg^-1 K^-1 for x = 0, 0.02, 0.05, and 1, respectively.

Abstract: Modeling study of magnetic and concentration phase transition in ultrathin films of diluted magnet has been carried out under approximation of random interaction between atomic magnetic moments of nearest neighbors and within the framework of Ising model. The dependence of Curie temperature on concentration of magnetic atoms was formed. It is shown that with increasing of thickness of ultrathin film the critical concentration of transition from unordered to ordered magnetic state decreases down to the value equal to the percolation threshold.

Abstract: Electric and magnetoresistive properties of La_0.6Sr_0.2Mn_1.2O₃ films deposited on SrTiO₃ (001) and LaAlO₃ (001) single crystalline substrates by magnetron sputtering have been studied. Characteristic features of the evolution of resistivity, magnetoresistance and Curie temperature upon the decrease of film thickness from 500 to 2 nm are specified. A key role of a thin strained layer adjacent to the substrate is demonstrated. The critical thicknesses of the strained layer are calculated for the films deposited on different substrates

Abstract: Some physical properties (such as lattice parameter, curie temperature, ac susceptibility) of Mg1-xZnxFe2O4 (where x = 0.3,0.4,0.5,0.6) ferrites have been studied. Magnesium Zinc Ferrites was synthesized by oxalate co-precipitation method at different synthesis temperature and characterized by X-ray diffraction and far IR absorption techniques, scanning Electron microscopy .The lattice parameter were computed. The X-ray diffraction studies reveal the formations of single phase cubic spinel structure.IR absorption bands are observed around 600 cm-1 and 400 cm-1 on the tetrahedral and octahedral sites respectively. Magnetization parameters such as saturation magnetization, and magnetic moment were calculated and the results are discussed with the help of the existing theories. Saturation magnetization was found to be in the range 2 emu/gm to 8.28 emu/gm when the samples were synthesized below 100°C. The variation of A.C. susceptibility with temperature shows the existence of super paramagnetic nature. The Curie temperature was determined from the measurement of the susceptibility verses temperature. The SEM micrograph shows the uniform distribution of the particles, the average size was estimated to be 0. 350 µm.

Abstract: In this paper shear type lithium niobate has been studied. The impedance-frequency characteristics were measured at high temperatures. This was carried out by placing the samples inside a furnace and performing in-situ impedance measurements at up to 600°C. The characteristic frequencies, capacitance, density and dimensions of samples were used to calculate the dielectric, elastic and piezoelectric coefficients. Prototype transducers were built using shear type lithium niobate crystals. The initial ultrasonic experiments show that it can be used at temperatures up to 450°C to transmit and receive guided wave signals at 70 kHz. This will enable design and manufacture of high temperature transducers for continuous guided wave monitoring of power plants.