1,071 research outputs found

    Spin Freezing in the Spin Liquid Compound FeAl2O4

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    Spin freezing in the AA-site spinel FeAl2_2O4_4 which is a spin liquid candidate is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl2_2O4_4 differs significantly from that of a canonical spin glass which is also supported by analysis of the nonlinear magnetic susceptibility term χ3(T)\chi_3 (T). Through the power-law analysis of χ3(T)\chi_3 (T), a spin-freezing temperature, TgT_g = 11.4±\pm0.9~K and critical exponent, γ\gamma = 1.48±\pm0.59 are obtained. Cole-Cole analysis of magnetic susceptibility shows the presence of broad spin relaxation times in FeAl2_2O4_4, however, the irreversible dc susceptibility plot discourages an interpretation based on conventional spin glass features. The magnetization measured using the cooling-and-heating-in-unequal-fields protocol brings more insight to the magnetic nature of this frustrated magnet and reveals unconventional glassy behaviour. Combining our results, we arrive at the conclusion that the present sample of FeAl2_2O4_4 consists of a majority spin liquid phase with "glassy" regions embedded.Comment: 5 pages, 6 figs, 2-column, Accepted to Phys. Rev.

    Large Magnetoresistance and Jahn Teller effect in Sr2_2FeCoO6_6

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    Neutron diffraction measurement on the spin glass double perovskite Sr2_2FeCoO6_6 reveals site disorder as well as Co3+^{3+} intermediate spin state. In addition, multiple valence states of Fe and Co are confirmed through M\"{o}ssbauer and X-ray photoelectron spectroscopy. The structural disorder and multiple valence lead to competing ferromagnetic and antiferromagnetic interactions and subsequently to a spin glass state, which is reflected in the form of an additional TT-linear contribution at low temperatures in specific heat. A clear evidence of Jahn-Teller distortion at the Co3+^{3+}-O6_6 complex is observed and incorporating the physics of Jahn-Teller effect, the presence of localized magnetic moment is shown. A large, negative and anomalous magnetoresistance of \approx 63% at 14K in 12T applied field is observed for Sr2_2FeCoO6_6. The observed magnetoresistance could be explained by applying a semi-empirical fit consisting of a negative and a positive contribution and show that the negative magnetoresistance is due to spin scattering of carriers by localized magnetic moments in the spin glass phase

    Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite Gd3_3Ir4_4Sn13_{13}

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    The magnetic, thermodynamic and electrical/thermal transport properties of the caged-structure quasi-skutterudite Gd3_3Ir4_4Sn13_{13} are re-investigated. The magnetization M(T)M(T), specific heat Cp(T)C_p(T) and the resistivity ρ(T)\rho(T) reveal a double-phase transition -- at TN1T_{N1}\sim 10~K and at TN2T_{N2}\sim 8.8~K -- which was not observed in the previous report on this compound. The antiferromagnetic transition is also visible in the thermal transport data, thereby suggesting a close connection between the electronic and lattice degrees of freedom in this Sn-based quasi-skutterudite. The temperature dependence of ρ(T)\rho(T) is analyzed in terms of a power-law for resistivity pertinent to Fermi liquid picture. Giant, positive magnetoresistance (MR) \approx 80%\% is observed in Gd3_3Ir4_4Sn13_{13} at 2~K with the application of 9~T. The giant MR and the double magnetic transition can be attributed to the quasi-cages and layered antiferromagnetic structure of Gd3_3Ir4_4Sn13_{13} vulnerable to structural distortions and/or dipolar or spin-reorientation effects. The giant value of MR observed in this class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of this work.Comment: 20 pages single column, 7 figures, 1 table; Accepted to J. Appl. Phys., 201

    A General Study on Langevin Equations of Arbitrary Order

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    In this paper, the broad study depends on Langevin differential equations (LDE) of arbitrary order.The fractional order is in terms of ψ-Hilfer fractional operator. This work reveals the dynamicalbehaviour such as existence, uniqueness and stability solutions for LDE involving ψ-Hilfer fractionalerivative (HFD). Thus the fractional LDE with boundary condition, impulsive effect and nonlocalconditions are taken in account to prove the result
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