Large Kerr Rotation Angle Research Articles

Element-selective magnetization states in a Gd23Fe67Co10 alloy, probed by soft X-ray resonant magneto-optical Kerr effect

The core-level resonant magneto-optical Kerr effect of a ferrimagnetic metal alloy, Gd23Fe67Co10, was measured at the Fe M-shell and Gd N-shell absorption edges using rotating analyzer ellipsometry. A large Kerr rotation angle of several degrees was detected at room temperature. The signal was found to be strong enough for element-selective magneto-optical experiments to trace various magnetic events, such as all-optical magnetization switching.

Observation of domain structure in non-collinear antiferromagnetic Mn3Sn thin films by magneto-optical Kerr effect

We perform hysteresis-loop measurement and domain imaging for (11¯00)-oriented D019-Mn3+xSn1-x (−0.11≤x≤0.14) thin films using the magneto-optical Kerr effect (MOKE) and compare it with the anomalous Hall effect (AHE) measurement. We obtain a large Kerr rotation angle of 10 mdeg, comparable with bulk single-crystal Mn3Sn. The composition x dependence of AHE and MOKE shows a similar trend, suggesting the same origin, i.e., the non-vanishing Berry curvature in the momentum space. Magnetic domain observation at the saturated state shows that x dependence of AHE and MOKE is explained by the amount of the reversible area that crucially depends on the crystalline structure of the film. Furthermore, in-depth observation of the reversal process reveals that the reversal starts with nucleation of sub-micrometer-scale domains dispersed in the film, followed by domain expansion, where the domain wall preferentially propagates along the [112¯0] direction. Our study provides a basic understanding of the spatial evolution of the reversal of the chiral-spin structure in non-collinear antiferromagnetic thin films.

Polar Kerr effect and perpendicular magnetic anisotropy in Fabry–Pérot cavity containing CoPt/AZO magneto-optical interference layer

We investigate the magneto-optical (MO) polar Kerr enhancement of Fabry–Pérot cavities with perpendicular magnetic anisotropy for chemical and biological sensing applications. The MO cavities consist of stacked films with a half-mirrored surface layer, a dielectric interference layer, a total-reflection mirror, and a magnetic metal layer. Co80Pt20 and Al-doped ZnO (AZO) thin films were utilized as the magnetic and interference layers, respectively. The cavities produce two types of MO enhancement depending on the thickness of the magnetic layer. The sample with a thick magnetic layer as a total-reflection mirror generates a single peak in the polar Kerr spectrum. Contrarily, inserting a several-nanometer-thick CoPt layer into the AZO layer produces a resonant-type spectrum. Although both samples generate large MO enhancement factors (>50), the magnetic properties significantly differ. The AZO/CoPt/AZO interference layer controls the crystalline and interface conditions and produces a square-shaped out-of-plane hysteresis loop with a large Kerr rotation angle. Moreover, the use of an ultrathin CoPt film significantly reduces the saturation magnetization field. Thus, Fabry–Pérot cavities with a CoPt/AZO interference layer may serve as high-sensitivity, low-energy-consumption sensor elements.

Measurement of the Resonant Magneto-Optical Kerr Effect Using a Free Electron Laser

We present a new experimental magneto-optical system that uses soft X-rays and describe its extension to time-resolved measurements using a free electron laser (FEL). In measurements of the magneto-optical Kerr effect (MOKE), we tune the photon energy to the material absorption edge and thus induce the resonance effect required for the resonant MOKE (RMOKE). The method has the characteristics of element specificity, large Kerr rotation angle values when compared with the conventional MOKE using visible light, feasibility for M-edge, as well as L-edge measurements for 3d transition metals, the use of the linearly-polarized light and the capability for tracing magnetization dynamics in the subpicosecond timescale by the use of the FEL. The time-resolved (TR)-RMOKE with polarization analysis using FEL is compared with various experimental techniques for tracing magnetization dynamics. The method described here is promising for use in femtomagnetism research and for the development of ultrafast spintronics.

Tunable magneto-optical effects in hole-doped group-IIIA metal-monochalcogenide monolayers

Because of unusual properties and fascinating prospects for next-generation device applications, two-dimensional (2D) materials have attracted enormous attention since graphene was discovered in 2004. Among the 2D materials beyond graphene, group-IIIA metal-monochalcogenide (MX) monolayers (MLs), are receiving increasing interests because their excellent applications on electronics and optoelectronics. Recently, ferromagnetism and half-metallicity have been predicted in hole-doped GaS and GaSe MLs, which promise exciting potentials for semiconductor spintronics. Detection and measurement of spontaneous magnetization in these 2D materials will be essential for their spintronic applications. The magneto-optical (MO) effects not only are a powerful probe of magnetism in 2D materials but also have valuable applications in high-density data-storage technology. Furthermore, anomalous Hall effect is not only an ideal transport probe of itinerant magnetism but also of considerable current interest because of its topological nature. Here we perform a systematic first-principles density functional study on the MO Kerr and Faraday effects as well as such important magnetic and transport properties as magneto-crystalline anisotropy energy (MAE) and anomalous Hall conductivity (AHC) of all hole-doped MX (M = Ga, In; X = S, Se, Te) MLs. In this paper, we report the following important findings: (a) gate-tunable MO effects in MX MLs in a broad range of hole concentration; (b) large Kerr and Faraday rotation angles with Kerr angles comparable to well-known MO 3d-transition-metal multilayers and Faraday angles being among the largest ones reported; (c) tunable MAE and large AHC, making MX MLs suitable for magnetic memory devices current-driven via spin-transfer torque and also promising materials for magnetic field nanosensors with high sensitivity. Superior MO characteristics, together with the other interesting properties, would make MX MLs an excellent family of 2D materials for semiconductor MO and spintronic nanodevices.

Sputtering preparation and magnetic properties of amorphous TbFeCo films

•Amorphous perpendicular TbFeCo films sputtered at low pressures exhibit high remanence ratio.•Temperature difference of ~40°C between Tc and Tcomp is determined in Tb-rich films.•A thin in-plane magnetization soft layer is revealed by MOKE measurements.•Large intrinsic polar Kerr rotation angle of ~0.2° @ 633nm is demonstrated.

Large magneto-optical Kerr effect in noncollinear antiferromagnetsMn3X(X=Rh,Ir,Pt)

Magneto-optical Kerr effect, normally found in magnetic materials with nonzero magnetization such as ferromagnets and ferrimagnets, has been known for more than a century. Here, using first-principles density functional theory, we demonstrate large magneto-optical Kerr effect in high temperature noncollinear antiferromagnets Mn$_{3}X$ ($X$ = Rh, Ir, or Pt), in contrast to usual wisdom. The calculated Kerr rotation angles are large, being comparable to that of transition metal magnets such as bcc Fe. The large Kerr rotation angles and ellipticities are found to originate from the lifting of the band double-degeneracy due to the absence of spatial symmetry in the Mn$_{3}X$ noncollinear antiferromagnets which together with the time-reversal symmetry would preserve the Kramers theorem. Our results indicate that Mn$_{3}X$ would provide a rare material platform for exploration of subtle magneto-optical phenomena in noncollinear magnetic materials without net magnetization.

Magnetic tunnel junctions using Co/Pt multilayered free layers with perpendicular magnetic anisotropy

Co/Pt multilayered films with perpendicular magnetic anisotropy have a large magneto-optical Kerr effect. To use the films with a submicron magneto-optical light modulator driven by spin transfer switching, we fabricated two types of magnetic tunnel junctions (MTJs) with Co/Pt multilayered films for the free layers. One is an fcc-based MTJ, another is a bcc-based MTJ with CoFeB/MgO/CoFeB junction. The fcc-based MTJ with a Ag buffer layer on the bottom electrode showed a large coercive force of the pinned layer, a large Kerr rotation angle of 0.3 degree in the free layer and a tunnel magnetoresistance (TMR) ratio of 3.8%. In the CoFeB/MgO/CoFeB junction, an X-ray diffraction pattern of an MgO layer showed a large MgO(002)-orientation. However, the TMR ratio was less than 3 %. An MTJ with a Ta buffer layer between the CoFeB layer and the Co/Pt multilayered films in the free layer was prepared. The Ta buffer was used to alleviate a lattice mismatch between bcc-CoFeB/MgO/CoFeB and fcc-Co/Pt multilayer. The peak intensity of the MgO(002)-orientation was increased up to 2 times. This result suggests that the crystalline texture of the bcc-CoFeB/MgO/CoFeB junction is strongly influenced by the fcc-Co/Pt multilayered films.

First-Principles Study of Structural, Electronic, Magnetic, Optical, and Magneto-Optical Properties of NpN

We study the structural, electronic, magnetic, optical, and magneto-optical properties of NpN in detail using the fully relativistic full-potential calculations based on the density functional theory within the local spin density approximation. We successfully reproduce the positive sign of the electric field gradient (EFG) at Np nuclei. The positive EFG is in striking contrast to the negative EFG in a Np 3+ free ion, indicating the importance of the interplay between spin–orbit coupling and covalent bonding in NpN. Also, the calculated band structure shows large splittings induced by spin polarization and spin–orbit coupling, suggesting that both effects are indispensable for understanding the electronic properties of this material. This results in a large Kerr rotation angle of about 2°, which is comparable to those of uranium calcogenides.

Effect of plasma excitation in Ag on optical and magneto-optical properties of CoPt particles

The optical and magneto-optical properties of Pt/Co(CoAg)/Pt films were investigated within the photon energy range of 1–4.5eV. A large Kerr rotation angle of about 0.6° was observed at photon energy ℏω≈4.1eV for the Pt/Co/Pt films after their annealing. The relevance of the interface alloying effect in Co/Pt systems for the explanation of experimental results is discussed. The correlation between the electron band structure of the Co–Pt alloys and the energy dependence of the optical and magneto-optical spectra in Pt/Co(CoAg)/Pt films has been investigated. It has been shown that the optical and magneto-optical properties for Pt/CoAg/Pt granular films can be enhanced by the effect of plasma resonance of free charge carriers in Ag.

X-ray Kerr rotation and ellipticity spectra at the2pedges of Fe, Co, and Ni

We present resonantly enhanced longitudinal magneto-optical Kerr rotation and ellipticity spectra measured across the $2p$ absorption edges of amorphous Fe, Co, and Ni. The Kerr spectra are acquired by a complete polarization analysis of linearly polarized synchrotron radiation upon reflection from the ferromagnetic films. We observe large Kerr rotation angles of up to $\ifmmode\pm\else\textpm\fi{}24\ifmmode^\circ\else\textdegree\fi{},$ more than two orders of magnitude larger than detected in the visible energy range. Spectral contributions stemming from atomic transitions could be separated from interference effects by simulations based on the optical constants, which have been determined through independent experiments. For grazing incidence, we show theoretically and experimentally that the longitudinal Kerr rotation and ellipticity spectra are related to transversal Kerr effect spectra and x-ray magnetic circular dichroism reflection spectra, respectively.

Interference effects in the X-ray Kerr rotation spectrum at the Fe 2p edge

We present longitudinal magneto-optical Kerr rotation spectra across the 2p absorption edge of a Fe film on Si substrate measured by means of polarization analysis upon reflection of linearly polarized synchrotron radiation. Large Kerr rotation angles of up to ±11° were detected, more than one order of magnitude larger than those observed in the visible range. An enhancement of the Kerr rotation is observed below the absorption edge due to interference effects. The spectra are successfully modelled using magneto-optical constants, which we determined independently.

The optical and magneto-optical properties of MnSbBi films

Abstract The optical and magneto-optical properties of Mn(Sb 1− x Bi x ) films were investigated for incident photons within the energy range from 1.3 to 4.0 eV. The diagonal and off-diagonal optical conductivities were determined from the results of spectroscopic ellipsometry and the polar Kerr effect measurements. A large Kerr rotation angle of about 0.57° was observed at photon energy ℏ ω ≈2.65 eV for the Mn 55 Sb 36 Bi 9 film with an average grain size of 30 nm. The changes of the exchange splitting and the spin–orbit interaction strength are responsible for the strong spectral dependence of the Kerr effect in Mn(Sb 1− x Bi x ) nanocrystalline films.

ＰｔＭｎＳｂ，ＭｎＢｉ，ＭｎＰｔ３の磁気光学Ｋｅｒｒスペクトルの第一原理計算

The magneto-optical Kerr spectra in PtMnSb, MnBi, and MnPt3 were calculated by the first-principles LMTO-ASA method. These three materials have large Kerr rotation angles of about 1-2 degrees in a low-energy region around 1-2eV. The large Kerr rotation peaks of the three materials are compared and discussed in detail.

The effect of boron on the uniaxial magnetic anisotropy energy and the polar Kerr rotation in amorphous NdFe films

Amorphous light rare earth–transition metal alloys are candidates for magneto-optical recording materials in the wavelength region of a blue laser beam (λ≈400 nm) due to the large Kerr rotation angle θK. However, the large demagnetizing energy (shape anisotropy) prevents the films from developing an effective perpendicular anisotropy. The addition of boron to the amorphous Nd Fe matrix reduces the magnetization, enhances the effective perpendicular anisotropy, and enhances the Kerr rotation angle θK.

Magnetic and magneto-optical properties of MnSb films on various substrates

Magnetic and magneto-optical properties of MnSb films with different crystalline orientations on various semiconductors of GaAs(1 0 0), GaAs(1 1 1)A, B, and sapphire(0 0 0 1) have been measured by a vibrating sample magnetometer (VSM) and a home-made magneto-optical Kerr effect (MOKE) system. All these samples have their easy axes in the plane and show ferromagnetic properties. Among these samples, the film on GaAs(1 1 1)B has the lowest coercive force H c and the largest squareness (SQ) value, whereas the film on GaAs(1 0 0) shows the largest H c and the lowest SQ value. A large Kerr rotation angle of about 0.3° was observed at a wavelength of λ=632.8 nm for the film on sapphire in the field applied both parallel and perpendicular to the film plane. However, the MnSn films on other substrates do not have an observable Kerr rotation. The dynamic effect of the hysteresis was also measured using our MOKE system. As the frequency of applied magnetic field increases, the loop rounds off at the corners and the loop area increases.

The origin of the 90 degree magneto-optical Kerr rotation in CeSb

We calculate the linear magneto-optical Kerr rotation for CeSb in the near-infrared spectral range. Using an exact formula for large Kerr rotation angles and a simplified electronic structure of CeSb we find at h ̷ ω = 0.46 eV a Kerr rotation of 90° which then for decreasing ω jumps to −90° as recently observed. We identify the general origin of possible 180° polarization rotations as resulting from mainly nonmagnetic optical properties, in particular from the ratio of the dominant interband resonance frequency to the plasma frequency. The dependence of the Kerr rotation on moments and magnetization is discussed.

Amorphous characteristics in spinel ferrites containing glassy oxides

Various kinds of flake-shaped amorphous ferrites have been produced by adding glassy oxides to spinel ferrites and furthermore by a rapidly quenching the molten ferrite. Various kinds of amorphous ferrite thin films have also been produced on a glass plate by means of a vacuum evaporation method. It was found that the magnetization of amorphous spinel ferrites is very low at room temperature, but becomes significantly larger at liquid helium temperature. Amorphous ferrite thin film possesses a large perpendicular anisotropy and a relatively large polar Kerr rotation angle. The results are discussed in connection with the Mössbauer spectra and the magnetic structure.

Improvement of magneto-optical properties of Co/Pt multilayers prepared by sputtering in Ar

We investigated methods for increasing the coercive force and the Kerr rotation angle and for reducing the Curie temperature of Co/Pt multilayers to make them suitable as magneto-optical recording media. The multilayers were prepared by magnetron sputtering using Ar gas. It was found that the coercive force increased with the magnetic flux density above the magnetron target and such an increase did not degrade the crystalline quality nor make less rectangular the Kerr hysteresis loops. The Kerr rotation angle increased when the number of layers per unit thickness was increased without changing the total Co content. The Curie temperature increased with Co content but was not affected by the number of layers. Therefore, Co content and number of layers per unit thickness were optimized in order to obtain a large Kerr rotation angle and a low Curie temperature. Moreover, read/write characteristics of a magneto-optical disk using the Co/Pt multilayer were examined: a carrier-to-noise ratio of 45 dB was obtained for a bit length of 0.76 μm.

LAYER MODULATED Co/Pt MULTILAYERS WITH ENHANCED KERR ROTATION ANGLES

Large Kerr rotation angles with a perfect squareness of hysteresis were obtained in Co/Pt multilayers by constructing a modulated layer structure. The Co/Pt multilayers were prepared by sputtering onto a SiO2 substrate. Multilayers with Pt interlayers showed large Kerr rotation angles up to 0.8 degree and stepwise hysteresis loops with a perfect squareness were also obtained. Optical calculation proved this Kerr enhancement to be due to optical interference and multiple reflection. Cu interlayers in the layer modulated multilayers substantially decreased the Kerr rotation. The authors have also found that very thin amorphous CoZrNb underlayer significantly improves coercivity.