Suja Elizabeth

Bio: Suja Elizabeth is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Magnetization & Antiferromagnetism. The author has an hindex of 25, co-authored 123 publications receiving 1727 citations.

Critical properties in single crystals of Pr1-xPbxMnO3

Abstract: The critical properties at the ferromagnetic-paramagnetic transition have been analyzed from data of static magnetization measurements on single crystals of ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Pb}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ for $x=0.23$ and $x=0.30$. In ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Pb}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$, the ferromagnetic ordering and the metal-insulator transition do not coincide in parts of the phase diagram. The crystal with $x=0.23$ is a ferromagnetic insulator with Curie temperature ${T}_{C}=167\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, while the crystal with $x=0.30$ has ${T}_{C}=198\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and remains metallic up to a metal-insulator transition temperature ${T}_{\mathrm{MI}}=235\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The dc magnetization measurements were carried out in the field range from $0\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ for an interval in the critical temperature range ${T}_{C}\ifmmode\pm\else\textpm\fi{}10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ corresponding to a reduced temperature interval $0.003l\ensuremath{\mid}ϵ\ensuremath{\mid}l0.06$. The exponents $\ensuremath{\beta}$ for spontaneous magnetization, $\ensuremath{\gamma}$ for the initial susceptibility above ${T}_{C}$, and $\ensuremath{\delta}$ for the critical magnetization isotherm at ${T}_{C}$ were obtained by static scaling analysis from modified Arrott plots and by the Kouvel-Fisher method for the insulating crystal with composition $x=0.23$. The data are well described by critical exponents similar to those expected for the Heisenberg universality class relevant for conventional isotropic magnets. Systematic deviations from scaling in the data for the metallic crystal with composition $x=0.30$ are demonstrated from effective critical exponents near the assumed ordering transition. The unconventional magnetic ordering in this system suggests the presence of frustrated magnetic couplings that suppress magnetic ordering and lower the transition temperature.

Critical properties of the double-exchange ferromagnet Nd(0.6)Pb(0.4)MnO(3)

Abstract: Results of a study of dc magnetization $M(T,H),$ performed on a ${\mathrm{Nd}}_{0.6}{\mathrm{Pb}}_{0.4}{\mathrm{MnO}}_{3}$ single crystal in the temperature range around ${T}_{C}$ (Curie temperature) which embraces the supposed critical region $|\ensuremath{\varepsilon}|=|T\ensuremath{-}{T}_{C}|{/T}_{C}l~0.05$ are reported. The magnetic data analyzed in the critical region using the Kouvel-Fisher method give the values for the ${T}_{C}=156.47\ifmmode\pm\else\textpm\fi{}0.06\mathrm{K}$ and the critical exponents $\ensuremath{\beta}=0.374\ifmmode\pm\else\textpm\fi{}0.006$ (from the temperature dependence of magnetization) and $\ensuremath{\gamma}=1.329\ifmmode\pm\else\textpm\fi{}0.003$ (from the temperature dependence of initial susceptibility). The critical isotherm ${M(T}_{C},H)$ gives $\ensuremath{\delta}=4.54\ifmmode\pm\else\textpm\fi{}0.10.$ Thus the scaling law $\ensuremath{\gamma}+\ensuremath{\beta}=\ensuremath{\delta}\ensuremath{\beta}$ is fulfilled. The critical exponents obey the single scaling equation of state $M(H,\ensuremath{\varepsilon})={\ensuremath{\varepsilon}}^{\ensuremath{\beta}}{f}_{\ifmmode\pm\else\textpm\fi{}}(H/{\ensuremath{\varepsilon}}^{\ensuremath{\beta}+\ensuremath{\gamma}}),$ where ${f}_{+}$ for $Tg{T}_{C}$ and ${f}_{\ensuremath{-}}$ for $Tl{T}_{C}.$ The exponent values are very close to those expected for the universality class of three-dimensional Heisenberg ferromagnets with short-range interactions.

Griffiths phase-like behaviour and spin-phonon coupling in double perovskite Tb$_{2}$NiMnO$_{6}$

Abstract: The Griffiths phase-like features and the spin-phonon coupling effects observed in Tb$_2$NiMnO$_6$ are reported. The double perovskite compound crystallizes in monoclinic $P2_1/n$ space group and exhibits a magnetic phase transition at $T_c \sim$ 111 K as an abrupt change in magnetization. A negative deviation from ideal Curie-Weiss law exhibited by 1/$\chi(T)$ curves and less-than-unity susceptibility exponents from the power-law analysis of inverse susceptibility are reminiscent of Griffiths phase-like features. Arrott plots derived from magnetization isotherms support the inhomogeneous nature of magnetism in this material. The observed effects originate from antiferromagnetic interactions which arise from inherent disorder in the system. Raman scattering experiments display no magnetic-order-induced phonon renormalization below $T_c$ in Tb$_2$NiMnO$_6$ which is different from the results observed in other double perovskites and is correlated to the smaller size of the rare earth. The temperature evolution of full-width-at-half-maximum for the {\it stretching} mode at 645 cm$^{-1}$ presents an anomaly which coincides with the magnetic transition temperature and signals a close connection between magnetism and lattice in this material.

Phase transitions and rare-earth magnetism in hexagonal and orthorhombic DyMnO3 single crystals

Abstract: The floating-zone method with different growth ambiences has been used to selectively obtain hexagonal or orthorhombic DyMnO(3) single crystals. The crystals were characterized by x-ray powder diffraction of ground specimens and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetization and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO(3) shows magnetic ordering of Mn(3+) (S = 2) spins on a triangular Mn lattice at T(N)(Mn) = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy(3+) (S = 9/2) spins. At T(N)(Dy) = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO(3) display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn(3+) spins at T(N)(Mn) = 39 K, a lock-in transition at T(lock-in) = 16 K and a second antiferromagnetic transition at T(N)(Dy) = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4f-4f and 4f-3d couplings.

Magnetization-steps in Y2CoMnO6 double perovskite: The role of antisite disorder

Abstract: Antisite disorder is observed to have significant impact on the magnetic properties of the double perovskite Y2CoMnO6 which has been recently identified as a multiferroic. A paramagnetic-ferromagnetic phase transition occurs in this material at Tc ≈ 75 K. At 2 K, it displays a strong ferromagnetic hysteresis with a significant coercive field of Hc ≈ 15 kOe. Sharp steps are observed in the hysteresis curves recorded below 8 K. In the temperature range 2 K ≤ T ≤ 5 K, the hysteresis loops are anomalous as the virgin curve lies outside the main loop. The field-cooling conditions as well as the rate of field-sweep are found to influence the steps. Quantitative analysis of the neutron diffraction data shows that at room temperature, Y2CoMnO6 consists of 62% of monoclinic P21/n with nearly 70% antisite disorder and 38% Pnma. The bond valence sums indicate the presence of other valence states for Co and Mn which arise from disorder. We explain the origin of steps by using a model for pinning of magnetization at the antiphase boundaries created by antisite disorder. The steps in magnetization closely resemble the martensitic transformations found in intermetallics and display first-order characteristics as revealed in the Arrott's plots.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Kirk-Othmer Encyclopedia of Chemical Technology数据库介绍及实例

Abstract: 介绍了Kirk—Othmer Encyclopedia of Chemical Technology（化工技术百科全书）（第五版）电子图书网络版数据库，并对该数据库使用方法和检索途径作出了说明，且结合实例简单地介绍了该数据库的检索方法。

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

Intermediate-spin state and properties of LaCoO_3

Abstract: The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.