8 research outputs found

    Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet

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    Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of two-dimensional (2D) van der Waals (vdW) materials. Herein, we report the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi2_\mathrm{2}Te3_\mathrm{3}, due to the proximity of FePS3_\mathrm{3} (an antiferromagnet (AFM), TNT_\mathrm{N} \sim 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi2_{2}Te3_{3} (106 cm1^{-1} and 138 cm1^{-1}) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi2_{2}Te3_{3} couple to phonons of similar frequencies of FePS3_3 in the AFM phase, has been adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic TNT_\mathrm{N} of FePS3_3 from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, our data suggest a double softening of phonon modes of Bi2_\mathrm{2}Te3_\mathrm{3} (at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible probe for delineating the magnetic ordering in bulk and surface of a hybrid topological insulator

    Aminoisophthalate Bridged Cd(II)-2D Coordination Polymer: Structure Description, Selective Detection of Pd<sup>2+</sup> in Aqueous Medium, and Fabrication of Schottky Diode

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    Photoluminescence activity of coordination polymers (CPs) has evoked intricate applications in the field of materials science, especially sensing of ions/molecules. In the present study, 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 5-aminoisophthalate (HAIPA–) coordinated to Cd(II) to architect a coordination polymer, {[Cd(HAIPA)(tppz)(OH)]·3H2O}n (CP1) which unveils blue emission in an aqueous acetonitrile (98% aqueous) suspension. The emission is selectively quenched by Pd2+ only without interference in the presence of as many as 16 other cations. The structure of CP1 shows the presence of a free –COOH group, and the interlayer (–CO)O(2)···O(7) (OC–) distance, 4.242 Å, along with the π···π interactions (3.990, 3.927 Å), may make a cavity which suitably accommodates only Pd2+ (van der Waal’s radius, 1.7 Å) through the Pd(II)-carboxylato (–COO–Pd) coordination. The stability of the composite, [CP1 + Pd2+] may be assessed from the fluorescence quenching experiment, and the Stern–Volmer constant (KSV) is 7.2 × 104 M–1. Therefore, the compound, CP1, is a promising sensor for Pd(II) in a selective manner with limit of detection (LOD), 0.08 μM. The XPS spectra of CP1 and [CP1 + Pd2+] have proven the presence of Pd2+ in the host and the existence of a coordinated –COO–Pd bond. Interestingly, inclusion of Pd2+ in CP1 decreases the band gap from 3.61 eV (CP1) to 3.05 eV ([CP1 + Pd2+]) which lies in the semiconducting region and has exhibited improved electrical conductivity from 7.42 × 10–5 (CP1) to 1.20 × 10–4 S m–1 ([CP1 + Pd2+]). Upon light irradiation, the electrical conductivities are enhanced to 1.45 × 10–4 S m–1 (CP1) and 3.81 × 10–4 S m–1 ([CP1 + Pd2+]); which validates the highly desired photoresponsive device applications. Therefore, such type of materials may serve as SDG-army (sustainable development goal) to battle against the environmental issues and energy crisis

    Anisotropic magnetodielectric coupling in layered antiferromagnetic FePS 3

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    We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic FePS3 (Néel temperature TN∼ 120 K) with perpendicular anisotropy. Above TN, while the dielectric response function along the c axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies
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