Preparation And Properties Of Magneto - Photonic Crystal Thin Films

Magneto-optical Kerr effect (MOKE) was first observed by John Kerr in1877. Kerr found rotation of the plane of polarization by reflection from the polished pole of an upright horseshoe electromagnet with polar surfaces perpendicular to the axes of the core of electromagnet. The magneto-optical Kerr effect can be explained in terms of Fresnel equations. The microscopic mechanism was studied to be attributed the interplay between the spin orbital coupling and exchange splitting by several authors, including Hulme, Argyres, Cooper, Kittle et al. The MOKE spectra can be sused to reveal the electronic structure in magnetic materials and semiconductors. With the MOKE, the magneto-optical storage technology and magneto-optical devices have been proposed. In this field, ideal magneto-optical materials with large MOKE have always been the aim of the researchers.This thesis consists of three parts. After description of the MOKE theory (Chapter1) and the experiment equipments (Chapter2) used in this work, we paid more attention to our work (Chapter3and4). Using polystyrene spheres (PSSs) self-organization, combined with the magnetron sputtering and electrochemical deposition, two series of magnetic photonic crystal films were fabricated, including magnetic films/PSSs (dielectric), and noble metal/magnetic anti-dot. And the polar MOKE was deeply analyzed.1. The fabrication and MOKE study of Fe/PSSs magnetic photonic crystal filmsThe two dimensional (2D) Fe/PSSs magnetic photonic crystal (MPC) films were fabricated on slides, using colloidal PSSs self-organized onto20nm Fe films. The periodic constants are determined by PSS diameter d. New phenomena were observed in the measured Kerr rotation and reflection spectra. Firstly, compared with pure Fe films,θk was enhanced in all measurement region for all samples with different d.θk and reflection spectra exhibited fine structure and achieved maxima and minima alternatively. The θk peaks correspond to the reflection dips one by one. Changing the PSS diameters from d=400nm to700nm, the location of θk peaks and reflection dips varied, and at the specific location d/λ, for all samples, the θk peaks exhibited similar shapes. At the location of d/A=0.78, and1.02, the θk peaks showed narrow bandwith near the reflection dips. The MOKE is sensitive to the optical properties of materials and the sensitivity S is determined by Where n(λ) is the complex refraction index of Fe/PSSs system, high S can be acquired at the location where λ=d.The reflection simulation was performed using the rigorous coupled wave analysis (RCWA) and the electromagnetic field (EF) distributions were simulated at specific wavelengths. The results showed that for the Fe/PSS samples the R minima arised from the surface plasmon-polariton (SPP)-like and guided modes (GMs). For the former modes, a large fraction of the EF magnitude was distributed at the Fe/PSSs interface, but the EF magnitude was almost confined to the PSSs for the latter modes. At the location of d/λ=0.78,1.02, the EF was mainly confined in the PSSs, and the narrow0k peaks were resulted from the GM. Both GM and SPP can be attributed to the surface modes, and the MOKE can be enhanced by both of them, but the Q factor of the MOKE may be different, the MOKE for the GM acquires high Q factor due to the low absorption of PS. Compared with pure Fe film, the optical properties of Fe/PSS were changed due to the surface modes, and the θk enhancement is mainly due to the pure optical constant effect.2. MOKE in sandwich structure Fe/PSSs/Au.The refraction index of polystyrene (PS) is1.6, which is closer to that of Air, and SPP can not be excited in the interface PSS/air. To modify the dielectric difference between PS and Air,10nm Au was sputtered onto the2D Fe/PSSs array. For this sandwitch Fe/PSSs/Au, both θk and εk displayed narrow peak at λ≈d, at half height, the bandwidth was as narrow as10nm. According to the formula! the Q factor of Fe/PSSs/Au was as high as0.3, larger than the value of0.2in ordinary magnetic materials, and this is helpful to modify the properities of magneto-optical devices.3. The fabrication and MOKE study of MgO/Ll0-FePt/PSSs magnetic photonic crystal films20nm L10-FePt films were prepared on MgO (100) single crystal substrates by dc magnetron sputtering at substrate temperatures620℃and in-situ post-annealing was performed at the same temperature for2h. The long range chemical ordering is clearly revealed by the X-ray diffraction peak at20=24°. The PSS arrays were fabricated on the FePt films by self-assembly to form Llo-FePt/PSSs MPC films. The Kerr loops of Llo-FePt and Llo-FePt/PSSs displayed the same coercivity but the value of θk was enhanced by a factor of2for the latter. The MOKE and reflection spectra exhibited the same tendency as that in Fe/PSSs sample, in addition to the resonance-like shape located near the d/λ=0.81, the sharp slop and high S were acquired. Compared with Fe/PSSs, we deduced that the modulation of MOKE in Llo-FePt/PSSs was also due to the pure optical effect.The Co anti-dot arrays were fabricated on glass/Cr/Ag (200nm) films using nanosphere lithography technology. The template Ag/PSSs was fabricated using colloid self-assebly onto Glass/Cr/Ag (200nm) films. Co film was electrodeposited into the interspace of PSS using three-electrode method. The Co anti-dot arrays were acquired with PSSs dissolved in tetrahydrofuran. Changing the deposition time and the constant lattice of the template, two series of samples were fabricated. The MOKE was modulated by both the plasma plasmons resonance of bulk Ag and the anti-dot structure resonance. The hole resonance and the lattice resonance competed With the varying of hole diameter and depth. The nanocavity mode was introduced to made the electromagnetic field (EF) redistributed when hole depth became larger than150nm, and high sensitivity was acquired. The magnetic measurements of the Co anti-dot were performed using magnetometry. Compred with continuous Ag/Co bilayers, the in-plane anisotropy was enhanced for all samples. And the anisotropy becomes strong with the lattice constant decreasing, but varied little with the hole depth and diameter.