Metallic Ferromagnet of La_0.5Sr_0.5MnO₃ with Negative Permittivity and Permeability

Abstract

geometrical arrangement and the dimensions of unit cells should be made considerably smaller than the characteristics of incident waves. [14][15][16][17][18] For instance, the dimensions of the microwave metamaterials need to be in the millimeter scale. As for infrared or visible metamaterials, only metallic nanostructures, particularly noble metals such as gold and silver with lower ohmic loss can sustain the optical waves. [19,20] To break the size scale and arrangement limits in the periodical-structured material design, random-structured metamaterials with inherent negative ε and/or μ are being sought. [21,22] So far, few theoretical and experimental works have focused on intrinsic single or double negative composites, including metal/ceramic composites and metal/polymer composites. [23][24][25][26][27][28][29][30][31][32][33] These composites are prepared by diluting the ferromagnetic metal or alloy fillers into insulating ceramics or polymers. The behavior of such composites heavily depends on the filler properties.Besides, numerous theoretical, computational, and experimental studies supported in exploring the metal-based composites and the single-phased (homogeneous) metamaterials with intrinsic double negative parameters. The target materials are focused on magnetic semiconducting CdCr 2 Se 4 , In 2−x Cr x O 3 , and La 2/3 Ca 1/3 MnO 3 , motivated by the coupling resonance mechanism between plasma and ferromagnetic resonances. [34][35][36] Veselago. predicted the behavior of metamaterial obtained from the magnetic semiconductor CdCr 2 Se 4 , but could not succeed because of considerable technological challenges in material synthesis. [34] Kussow and Akyurtlu theoretically predicted that, in polycrystalline form, the homogeneous magnetic semiconductor In 2−x Cr x O 3 should exhibit a negative refractive index at ≈10.48 THz. [35] For epitaxial La 2/3 Ca 1/3 MnO 3 film grown on MgO substrate, the negative magnetic μ has been estimated from transmittance data by assuming μ = 1 in the geometry h//μ 0 H. However, the reduction of the anisotropy for different incident angles remains the most difficult. [36] It can thus be concluded that homogeneous or single-phase metamaterials have not yet been realized experimentally.Metallic ferromagnet is believed to be a good candidate for single-phase metamaterials with simultaneous negative ε and μ. Perovskite manganite of La 1−x Sr x MnO 3 (0.2 ≤ x ≤0.5) is a metallic ferromagnet due to the Double-Exchange (DE)Since the electromagnetic metamaterials are artificial materials with subwavelength-scale periodic architectures, they can manipulate electromagnetic waves by exhibiting unusual properties of characteristic negative permittivity ε and permeability μ. However, their fabrication toward reducing the anisotropy for the realization of practical metamaterials is still a challenge. A homogeneous La 0.5 Sr 0.5 MnO 3 with negative properties synthesized by a facile method consisting of the sol-gel method and pressure-less sintering is proposed in this paper. By appropriate...

Modified Lossy epsilon-negative CuCr2Se4 toward single-phase metamaterials with double negative parameters via Zn doping

“…Because of the enhanced symmetry of the crystal, the splitting bimodal pattern converts to a single peak. 28…”

“…37 CuCr 2 Se 4 e x hibits metallic ferromagnetism since e g electrons can “cruise” between Cr 3+ and Cr 4+ ions only if the spins of the electrons of the ions are parallel. 28 The interaction between two Cr 3+ ions through intermediate Se 2− ions is called super-exchange. ZnCr 2 Se 4 exhibits antiferromagnetism, due to the super-exchange interactions of Cr 3+ –Se 2− –Se 2− –Cr 3+ .…”

“…Considering the skin effect, the real part of the permeability is e x pressed as follows: 28,34 where V δ signifies the volume of the material within the skin depth δ , V denotes the volume of the material, d represents the thickness of the material, n represents the ratio of the skin depth to the penetration depth, μ m represents the effective permeability, ω represents the angular frequency of the applied magnetic field ( ω = 2π f ), ω d represents the resonance frequency of the domain wall, χ d0 denotes the domain wall susceptibility, α denotes the damping factor of the domain wall; ω s represents the resonance angular frequency of the spin component, χ s0 denotes the spin susceptibility, and β denotes the spin damping factor. According to the permeability and static conductivity at 1 Hz, the skin depths of Cu 1− x Zn x Cr 2 Se 4 ( x = 0, 0.2, 0.4, 0.6, 0.8) can be calculated as 1.24 mm, 2.46 mm, 2.49 mm, 3.00 mm and 6.76 mm, respectively.…”

“…Thus, negative values of and negative values of were attained in the frequency range of 575–650. 28 Veslago considered utilizing semiconductive spinels as potential candidates for single-phase metamaterials. However, the synthesis process was proven to be challenging, the particle size of the spinel has an important effect on the performance, 29 and ion doping will also cause lattice distortion, 30 which further affects the performance, and ultimately leads to failure.…”

Negative Correlation Between Thermal and Electrical Conductivity in Epsilon‐Negative Nanocomposites

“…Plasma oscillations are the collective behavior of electrons when a perturbation is introduced, for example, by applying an external electric field, electrons would rapidly oscillate at certain equilibrium positions (Figure S1, Supporting Information). [ 29 ] When plasma oscillations induced within the conducting network constructed by naked MWCNTs are cut off through the PDA layer, which confines electrons within MWCNTs, resulting in the generation of localized plasma oscillations ( Figure a). To better understand localized plasma oscillations and how they affect thermal and electrical conductivity in ENMs, we analyze the electrons' state in localized mode.…”