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Magneto-plasmonics in Purely Ferromagnetic Sub wavelength Arrays
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
S. D. Pappas, E. Th. Papaioannou
The magneto-optical Kerr effect (MOKE) refers to the change of the polarization state of the linearly polarized incident light when the latter is reflected from the surface of a magnetic material. For the appearance of the magneto-optical effect, two requirements have to be simultaneously fulfilled: (i) spin polarization (or generally magnetization) and (ii) Spin-orbit coupling. The spin polarization causes the cancelation of the degeneration of spin-orbit-coupled states, so that different complex refractive indexes appear for right-circular polarized light (RCP) ñ+ (ω) and left-circular polarized light (LCP) ñ- (ω), respectively, where ω is the angular frequency of light. The complex refractive index of a material is a unit-less frequency-dependent physical quantity. It can be written as the sum of a real part (refractive index) n(ω) and an imaginary part (absorptive index) k(ω)P n˜(ω)=n(ω)+iκ(ω)
Magnetic Structures of 2D and 3D Nanoparticles
Published in Jean-Claude Levy, Magnetic Structures of 2D and 3D Nanoparticles, 2018
The electromagnetic field of light interacts with the spin magnetic moments, giving rise to a magnetic susceptibility. This leads to the absorption and polarization of light by transmission, the so-called Faraday effect [74], and by reflection, the Kerr effect, also called magneto-optical Kerr effect (MOKE) [77]. From the previous observations it sounds that global Faraday effect is hard to understand even when samples do not absorb light too strongly since it results from the interaction with many different layers, while Kerr effect is just sensitive to a thin surface layer. So Kerr effect reveals the state of magnetization at the surface with a wavelength resolution. And so MOKE was largely used for thin films and ultrathin films with perpendicular anisotropy which show bubble-like magnetic domains [68], considered for magnetic memories [17]. At this time MOKE revealed the existence of magnetic stripes, chevrons, and labyrinths [125], as well as of magnetic bubbles. Now, when considering small samples, the advantage of MOKE remains its capacity of fast integration of the magnetization component over the sample. So now MOKE is mainly used to observe hysteresis cycles of nanoparticles [107] in the presence of variable external fields, usually in parallel with numerical micromagnetic simulations with the basic code OOMMF [45]. Such a combination of experiment and simulation enables the experimentalist to explain the singularities of hysteresis loops by changes in magnetic configuration.
Magnetic Recording
Published in David Jiles, Introduction to Magnetism and Magnetic Materials, 2015
The reading of magnetic information on the medium depends on the magneto-optic Kerr effect. A polarized laser beam, with lower intensity (lower number of watts per square millimeter) than that used for writing is reflected from the surface of the magnetic recording medium, as shown in Figure 14.8. The laser light beam is then passed through a polarized analyzer before being detected. The presence or absence of the reverse domains can then represent either 0 or 1. The film can later be wiped clean by saturating the magnetization in the original direction. It should be noted that for purposes of detection this technique works best in perpendicularly magnetized media. Signal-to-noise ratios are comparable with conventional magnetic disk recording. Magneto-optic disks typically have a 50 nm thick magnetic coating on a transparent 3 mm thick plastic substrate and use a 3 mW laser with a spot size of 2 × 5 μm to read the information on the disk by the Faraday and Kerr effects.
Two-dimensional functional materials: from properties to potential applications
Published in International Journal of Smart and Nano Materials, 2020
Yining Wei, Xiao Tang, Jing Shang, Lin Ju, Liangzhi Kou
As a 2D magnetic material, the spintronic device can be proposed based on the magnetic properties of CrI3. A gated bilayer CrI3 device is fabricated to realize a metamagnetic transition by electrostatic gate controlling [47]. The device is illustrated in Figure 8(a), consisted of a bilayer CrI3 flake and a graphite contact. The magnetization could be probed by magneto-optical Kerr effect (MOKE) microscopy. From Figure 8(b), the light color indicates low MOKE signal, which refers to the AFM state, the dark colors represent the two FM states. The metamagnetic transition lies on the back-gate voltage Vbg. As revealed by the reflectance magneto-circular dichroism (RMCD) microscopy, the applied gate voltage would induce interlayer bias and electrostatic doping. The critical field between FM and AFM (Figure 8c) could be affected by doping level while the doping could control orbital occupation, exchange interactions as well as the magnetic coupling [100–103]. This work designed a new device based on bilayer CrI3 to explore magnetoelectric effects and their potential applications in gate-tunable spintronics.
Magnetooptical Analysis of the Subsurface Region in a Bearing Ring Subjected to Rolling Contact Fatigue
Published in Tribology Transactions, 2018
Yuri Kadin, Iacopo Bertelli, Andrei Kirilyuk
The current work presents an experimental study that aims to understand whether the RCF material alterations visualized as DERs and WEBs lead to changes in the magnetic properties of steel. For this we use the magnetooptical Kerr effect (MOKE), which describes the changes in light polarization upon reflection from a magnetized surface. MOKE is a conceptually simple technique that allows quick measurements with high spatial and temporal resolution. Therefore, it is applied for investigation of the magnetic properties in different materials; for example, steel (Koschny and Lindner (11)), superconductors (Wells, et al. (12)), and semiconductors (Yada, et al. (13)).