Au-Encapsulated Fe Nanorods in Oxide Matrix with Tunable Magneto-Optic Coupling Properties

Abstract

Materials with magneto-optic coupling properties are highly coveted for their potential applications ranging from spintronics and optical switches to sensors. In this work, a new, three-phase Au–Fe–La0.5Sr0.5FeO3 (LSFO) hybrid material grown in a vertically aligned nanocomposite (VAN) form has been demonstrated. This three-phase hybrid material combines the strong ferromagnetic properties of Fe and the strong plasmonic properties of Au and the dielectric nature of the LSFO matrix. More interestingly, the immiscible Au and Fe phases form Au-encapsulated Fe nanopillars, embedded in the LSFO matrix. Multifunctionalities including anisotropic optical dielectric properties, plasmonic properties, magnetic anisotropy, and room-temperature magneto-optic Kerr effect coupling are demonstrated. The single-step growth method to grow the immiscible two-metal nanostructures (i.e., Au and Fe) in the complex hybrid material form opens exciting new potential opportunities for future three-phase VAN systems with more versatile metal selections.

Self‐Assembled Metal–Dielectric Hybrid Metamaterials in Vertically Aligned Nanocomposite Form with Tailorable Optical Properties and Coupled Multifunctionalities

“…A recent study of a new three‐phase Au–Fe–La 0.5 Sr 0.5 FeO 3 hybrid thin film [ 56 ] demonstrates the MOKE properties because of the coexisting plasmonic metal Au and ferromagnetic metal Fe, as shown in Figure 9c,d. For the polar configuration, both the laser and magnetic field were applied at 0° incidence to the film surface, whereas for the longitudinal configuration, the laser imposes at 30° incidence while the magnetic field was applied along the IP direction.…”

“…As for the VAN hybrid metamaterial systems, vastly different ε || and ε ⊥ values are exhibited due to the strong anisotropic pillar‐in‐matrix structure. The IP ε || and OP ε ⊥ components of several explored metal–oxide VAN systems including Au–BTO, [ 44,46 ] Fe–BTO, [ 53 ] Au–La 0.67 Sr 0.33 MnO 3 (LSMO), [ 54 ] Au–BTO–ZnO, [ 55 ] and Au–Fe–La 0.5 Sr 0.5 FeO 3 (LSFO), [ 56 ] in the wavelength range of 400–1000 nm are shown as red outlined rectangular regions in the diagram. Currently, most of the explored metal–oxide VAN systems have negative ε metallic nanopillars embedded in a positive ε dielectric matrix, leading to ε || > 0, ε ⊥ < 0 (schematic illustration shown on the bottom right in the diagram), epsilon‐near‐zero (ENZ) and hyperbolic dispersion characteristics.…”

“…[47][48][49][50][51][52] The permittivity of common oxides, nitrides, carbides, and several explored VAN hybrid system in the wavelength range of 400-1000 nm are plotted in Figure 2. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] It can be seen that most of the pure oxides, carbides, and nitrides have isotropic positive permittivity values, i.e., nearly equal positive ε || and ε ⊥ values due to the (pseudo-) centrosymmetric structures. Thus the range of their permittivity values are located in the light-blue elliptical region in the first quadrant of the diagram, with a few exceptions of transition metal nitrides (i.e., TiN, HfN, and ZrN) with both negative ε || and ε ⊥ located in the third quadrant of the diagram.…”

“…IP (ε || ) and OP (ε ⊥ ) permittivity diagram of oxides, nitrides, carbides, and several reported metal-oxide, oxide-oxide VAN systems at wavelength from 400 to 1000 nm. [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] Insets are two schematic illustrations of two types of VAN hybrid films: i) ε || > 0, ε ⊥ < 0 (shown on bottom right) and ii) ε || < 0, ε ⊥ > 0 (shown on top left).…”

“…Fe-BTO, [53] Au-La 0.67 Sr 0.33 MnO 3 (LSMO), [54] Au-BTO-ZnO, [55] and Au-Fe-La 0.5 Sr 0.5 FeO 3 (LSFO), [56] in the wavelength range of 400-1000 nm are shown as red outlined rectangular regions in the diagram. Currently, most of the explored metal-oxide VAN systems have negative ε metallic nanopillars embedded in a positive ε dielectric matrix, leading to ε || > 0, ε ⊥ < 0 (schematic illustration shown on the bottom right in the diagram), epsilonnear-zero (ENZ) and hyperbolic dispersion characteristics.…”