Longitudinal Magneto-optical Kerr Effect Research Articles

Magnetooptic Effect of Fe-Ni, Ni-Co and Fe-Co Binary Alloy Films

The longitudinal magnetooptic Kerr effect in evaporation-deposited Fe-Ni, Ni-Co and Fe-Co binary alloy films was measured in order to clarify the relationship between the magnetooptic Kerr effect and the saturation magnetization M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . The results show that the relationship between the Kerr rotation θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> and M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> can be expressed as θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> ∝M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> 1.7-2.1 at λ=400 to 1000 nm. The magnetooptic parameter Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , which is a measure of the magnitude of the magnetooptic effect, is not only dependent on the M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , but also on the crystal structure.

Simultaneous in-plane Kerr effects in Fe/GaAs (110) thin films

For many materials that can be magnetized, part of the magnetization process may be attributed to a rotation of the magnetization vector. In this context, a combination of the longitudinal and transverse magneto-optical Kerr effects are used to detect two orthogonal magnetization components in single-crystal Fe/GaAs (110) thin films. Hysteresis curves obtained by this magneto-optical technique are presented for fields along the in-plane [001], [11̄0], and [11̄1] crystal directions. For those curves that show signs of rotation, these data are simulated using a coherent rotation mechanism for the magnetization process and Fresnel reflection coefficients for the two Kerr effects. From the experimental data, it is found that the [11̄1] curves have shapes that are indicative of a rotational process. On the other hand, both the [001] and [11̄0] have magnetization curves that do not follow a simple rotation. From the coherent rotation model, there is qualitative agreement between the modeled and experimental data for the [11̄1].

Use of the longitudinal magneto-optical Kerr effect to study nonmagnetic/magnetic bilayers

We report the results of longitudinal magneto-optical Kerr effect (LMKE) measurements on bilayers consisting of a thick permalloy film covered by varying thicknesses of Nb. The LMKE pertains to situations in which light with a finite angle of incidence is reflected from a plane surface, and M in the sample is parallel both to the plane of incidence and the surface. Either s- or p-linearly polarized 6328-Å light is incident on the sample at 60° to the normal. The two components of the complex Kerr rotation are measured with a modulation technique utilizing a λ/4 plate and a Faraday rotator driven by dc and 2000-Hz signals. With cycling of an in-plane magnetic field, square magneto-optical hysteresis loops are observed in both rotation and ellipticity. There is a change in sign, as well as a decrease in the magnitude of the switching discontinuity in these quantities with increasing overlayer thickness. These results are very similar to those of the corresponding idealized boundary value problem. The technique gives experimental information on the magnetic properties of films buried below a nonmagnetic material or of thin films bounded on both sides by a nonmagnetic material. Further, it gives a probe of the phase and intensity of optical frequency electric fields below a reflecting surface.

SEMPA domain observation compared to three other methods

SEMPA (scanning electron microscopy with polarization analysis) is compared to well-known methods of magnetic imaging, Bitter colloid, longitudinal magnetooptical Kerr effect (MOKE), and Lorentz transmission electron microscopy (LTEM), with no extraordinary image processing. Resolution is established by direct micrograph measurement of the smallest structure available. The images have been acquired using a thin-film (35-nm) Permalloy chevron-shaped object. Bitter images gave their usual delineation of domain walls. Longitudinal MOKE images produce results similar to Bitter images; however, diffraction patterns near the chevron's boundary blurred the magnetic information. The LTEM micrographs provided by far the most qualitative data about the magnetization of the chevron; magnetization ripple structure was apparent. SEMPA images are produced with the highest magnification, 5000*, and the present generation of instrumentation did provide quantitative information about surface magnetization. However, the angle of magnetization in the plane of the film suffers from instrumental and electronic asymmetries. The magnitude of magnetization information appears to be consistent, even though it is uncalibrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A method for the magneto-optic imaging of magnetization time evolution in thin films

We describe a digital imaging technique with a spatial resolution of less than 0.5 μm that allows the observation of the nucleation and growth of magnetic domains in metallic films whose surfaces are under less than ideal conditions. A diffraction limited laser spot is scanned across the surface of interest while a periodic magnetic field of saturation strength is applied. The local magnetization curve under each point of the laser scan is measured through the longitudinal magneto-optic Kerr effect and recorded in a computer. From the stored data, the spatial distribution of the magnetization component in one direction as a function of time is obtained. Digital averaging and data normalization are used to enhance the quality of the images which allows the optical imaging of very rough surfaces. To demonstrate the technique, the pole tip region of a film recording head was imaged and the magnetization distribution in that region was observed as a current waveform was applied to the coils of the head. In the present implementation, a time resolution of 50 ns was achieved.

Fiber optic interferometric and ferromagnetic resonance studies of Fe81B13.5Si3.5C2

Amorphous films 3.5 μm thick of Fe81B13.5Si3.5C2 were deposited using conventional radio-frequency sputtering on planar glass substrates and cladded single-mode optical fibers of 80-μm diameter with a core diameter of 4 μm. The substrates were arranged in two configurations. In the first configuration the substrates (group I) were placed in contact with the water-cooled substrate table; in the second configuration (group II) the substrates were suspended about 8 mm above the substrate table. Ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) measurements were used to study the bulk properties of the film and the longitudinal magneto-optical Kerr effect was used to study the magnetic hysteresis at the film surfaces. The group (I) samples were found to be magnetically softer than their group (II) counterparts. The magnetostrictive response of the coated fibers was studied using a Mach–Zehnder interferometer. The dependence of this response on annealing is also discussed.

Optical and neutron domain structure studies of amorphous ribbons

The domain configuration of amorphous ribbons with positive, vanishing and negative magnetostriction constant λ s has been investigated by means of the longitudinal magneto-optical Kerr-effect and a three-dimensional neutron depolarization analysis. The influence of an external tensile stress on the domain arrangement depends on the sign and the magnitude of the magnetostriction constant and could be measured quantitatively in the depolarization experiment. With the aid of the optical observations domain models have been established; these models were tested and completed by means of an analytic calculation of the corresponding depolarization matrix and a comparison with experimental data. Domain reorientation processes within the ribbons under an imposed tensile stress were found to agree with theoretical predictions. The nearly nonmagnetostrictive alloys shows neither stripe domains nor simple wide domains but a more complicated structure with several layers of domains.

Magnetization processes of iron whiskers in small magnetic fields

The magnetization behaviour of iron whiskers in de magnetic fields has been investigated using the enhanced longitudinal magneto-optic Kerr effect [6]. The experimental results were compared with the phenomenological membrane model [1] and also with magneto static calculations.

Observation of a new domain configuration in polycrystalline FeSi films

FeSi films have been rf sputtered on glass, fused silica, and Si substrates. Sputter targets of 2 and 7 wt% Si were used, and the film thickness was varied between 0.1 and 4 μm. Several films, especially those on glass in the 0.5-μm-thickness range, showed a characteristic roughly rectangular domain structure. The films were isotropic. The structure has been analyzed with the longitudinal magneto-optic Kerr effect by rotating either the film or the demagnetizing field in the film plane. The magnetization made an angle of about 18° with the longer walls. A new magnetization process, ``wall rotation'', could be observed.