Kerr Rotation Angle Research Articles

MO Kerr study of the 4f 1 state

Recent measurements of the magneto-optical Kerr effect of the cerium monochalcogenides and monopnictides have brought a deeper insight into the character of the 4f 1 state. In these materials, the 4f → 5d transitions give rise to very sharp and larger Kerr rotation peaks. Among these, one finds the three largest ever measured Kerr rotation angles of 90°, 22.1° and 9.2° for cleaved single crystals of CeSb, CeS and CeBi, respectively. Furthermore, for the 4f 1 level, the effect of pf mixing has been found to be significant.

Perpendicular magnetic anisotropy and magnetooptical properties of (Co/sub 1-x/Ni/sub x/)/Pd multilayers

The magnetic and magnetooptical properties of (Co/sub 1-x/Ni/sub x/)/Pd multilayers were systematically investigated. The addition of Ni to the Co layer simultaneously decreases the Curie temperature and Kerr rotation angle, but the decrease of the Curie temperature is larger. By controlling the Ni content it is possible to reduce the Curie temperature. The perpendicular magnetic anisotropy energy also decreases with the addition of Ni, but the change is small. The interfacial anisotropy energy and volume anisotropy energy were calculated and discussed. Adding Ni to the Co layer can yield control of magnetic and magnetooptical properties, while maintaining a large effective perpendicular anisotropy energy.

Properties of Magneto-Optical Co-Pt and Magnetoresistive Co-Cu Alloy Films

ABSTRACTCo-Cu films of 1000 – 1500 Å thick were produced by means of flash-evaporation technique at 150 K, 400 K, 520 K and 720 K. The Co022Cu078 films produced at 400 K or 520 K exhibit the maximum value of MR of 16.5% at 77 K and 1.5 T. Co-Pt films of 200 Å thick with Pt buffer layers of 200 Å thick were prepared at room temperature (RT) by ultrahigh-vacuum cosputtering. The saturation polar Kerr rotation angles (θk) at RT of CoPt3 film are all larger than those of the Co/Pt multilayered (ML) film of the corresponding composition. The surface morphology, mean grain and magnetic domain sizes, and size distributions of the grains and magnetic domains of the Co alloy films have been investigated by magnetic force microscopy (MFM) and atomic force microscopy (AFM). The results were correlated with those obtained by using MO and optical spectroscopy at both RT and low temperatures (LT) in a spectral ramge of 0.5 – 4.4 eV, and magnetic investigations at both RT and LT including field-dependence measurement of MR. The overall results reflect the changes in the electronic structures and magnetic states of the constituent elements, induced by the structural transformation or correlated with the structures of the films.

A recording process simulation for double-layered magneto-optical disk

Magnetic Multi-Valued (MMV) recording process is studied by numerical simulation including thermomagnetic effect. A medium, which consists of PtCo capping layer coupled to TbFeCo recording layer, switches the signal of Kerr rotation angle responding to the external field in four levels. The time evolution of generated pattern of recording mark is calculated by extending the previous magneto-optical (MO) recording simulation for single layer system.

Magnetically Induced Superresolution Using Interferential In-Plane Magnetization Readout Layer

A magnetically induced superresolution (MSR) readout method using an in-plane magnetization mask was investigated. The magnetooptical disk consisted of an interference layer, a readout layer, a transparent intermediate layer, a recording layer and a protective layer. The use of the readout layer enabled center aperture detection which was suitable for a mark edge readout system. In this investigation, the film thickness of the readout layer was 20 nm, so the polar Kerr rotation angle is enhanced because of optical interference. The use of the interferential MSR readout method with an in-plane magnetization mask enabled excellent readout and recording characteristics to be obtained.

Derivation of simplified analytic formulae for magneto-optical Kerr effects

We have derived simplified analytic expressions for various magneto-optical Kerr effects of an optically thick medium having an arbitrary magnetization direction. We have found that the simplified formulae for the Kerr effects of p and s waves consisted of a product of two factors: the prefactor dependent pure optical parameters of the system and the main factor of the polar Kerr effect for a normal incidence case. The measured magneto-optic polar Kerr rotation angles of Co/Pd multilayers and the longitudinal Kerr rotation angles of Cu/Co multilayers with varying incident angles could be well fitted using the simplified analytical formulae.

Study of the enhancement effects of composite films on the magneto-optical Kerr effect

Computer numerical simulations have been performed to study the enhancement effects on the polar Kerr rotation angle and signal-to-noise ratios by the inclusion of ceramic-metal composite materials in multilayered arrays. The polar Kerr rotation angles, reflectivity and figures of merit have been calculated as functions of the wavelength of the incident radiation for arrays including magneto-optical, dielectric, metallic, and composite films. The spectral positions and magnitudes of the maxima of these curves are compared with equivalent results for magneto-optical films deposited on metallic substrates.

Determination of the off-diagonal element of the dielectric tensor without measuring the ellipticity

In addition to the measurement of the Kerr rotation angle, the measurement of the ellipticity is generally known to be necessary for determining the off-diagonal element of the dielectric tensor. We have found a new method for determining the off-diagonal element of the dielectric tensor, without measuring the ellipticity, for a sample deposited on a transparent substrate.

Theory of nonlinear magneto-optics (invited)

Nonlinear magneto-optics is a very sensitive fingerprint of the electronic, magnetic, and atomic structure of surfaces, interfaces, and thin ferromagnetic films. Analyzing theoretically the nonlinear magneto-optical Kerr effect for thin films of Fe(001) and at Fe surfaces we demonstrate exemplarily how various electronic material properties of ferromagnets, such as the d-bandwidth, the magnetization, the substrate lattice constant, and the film-thickness dependence can be extracted from the calculated nonlinear Kerr spectra. Furthermore, we show how the substrate d electrons [Cu(001)] affect the nonlinear Kerr spectra even without being themselves spin-polarized and without film-substrate hybridization. We show that the Kerr rotation angle in second-harmonic generation is enhanced by one to two orders of magnitude compared to the linear Kerr angle and how symmetry can be used to obtain the direction of magnetization in thin films and at buried interfaces from nonlinear magneto-optics.

Magnetic properties and magnetization reversal in Co/Au multilayers (abstract)

We report studies of magnetic properties in CoX Å/Au60 Å multilayers (X=5,6,7,8,12,20 Å), which were prepared by sputtering on Si(111) substrates, with emphasis on the magnetization reversal. Magnetization reversal was investigated by measurements of initial magnetization curves, minor loops, coercivity as a function of the maximum field of minor loops, temperature dependence of magnetic properties using Kronmüller’s model, time decay of Kerr rotation angle ΘK, and the field-sweep speed dependence of coercivity Hc(dHa/dt) at room and/or low temperature. It is found that (1) the thermal activation volumes determined by Hc(dHa/dt) increase from ∼2.0×10−17 to ∼9.9×10−17 cm3 as X varies from 5 to 20 Å, which corresponds to a cylindrical activation volume with ∼800 Å diameter. (2) A Kronmüller analysis together with the initial magnetization curves, etc., for a Co5 Å/Au60 Å sample at room and low temperature indicates that wall pinning with small pinning sites is the major coercivity mechanism. The interaction between grains was studied with the so-called ΔM method: samples with thin Co layers (X=5,6,7 Å), which show perpendicular anistropy, exhibit negative ΔM or dipolar interactions, while samples with a thick Co layer (e.g., X=20 Å), which show in-plane anisotropy, exhibit positive ΔM or ferromagnetic exchange interactions.

Manipulation of the spin-orbit coupling using the Dirac equation for spin-dependent potentials.

A scheme is presented that allows us to manipulate the spin-orbit coupling in calculations based on the Dirac equation for spin-dependent potentials. To demonstrate its application, the spin and orbital magnetic moments for the disordered alloy ${\mathrm{Fe}}_{0.20}$${\mathrm{Ni}}_{0.80}$ as well as the Kerr rotation angle ${\mathrm{\ensuremath{\theta}}}_{\mathit{K}}$ of pure Ni have been calculated as a function of the spin-orbit coupling strength. While the spin moment changes only slightly, the orbital moment as well as the Kerr rotation angle ${\mathrm{\ensuremath{\theta}}}_{\mathit{K}}$ increase almost linearly with the spin-orbit coupling strength. \textcopyright{} 1996 The American Physical Society.

Magnetic anisotropy and magneto-optical Kerr effect of metallic multilayers

We prepared multilayers on glass substrates by RF magnetron sputtering at room temperature. multilayers exhibit a magnetic easy axis perpendicular to the film plane up to a larger magnetic layer thickness than do Co/Pd multilayers. In particular, multilayers became perpendicular at 33 Å. The magnetic anisotropy can be explained by the strain effect. The role of the magnetoelastic energy due to the in-plane strain in the system is pointed out and discussed. We also investigated the magneto-optical polar Kerr effect of these multilayers. The polar Kerr rotation angle increases when the Au concentration is 4.5 at.% compared to Co/Pd multilayers but decreases with increasing Au content.

MAGNETIC, MAGNETO-OPTICAL AND DYNAMIC CHARACTERISTICS OF EXCHANGED-COUPLED NdTbFeCo/TbFeCo FILMS For 532 NM RECORDING MEDIA

In this work, we have studied the magneto-optical (MO) and the dynamic behavour of exchanged-coupled (EC) layers between the Nd16Tb14Fe52Co18 (at. %) films for the read-out (RO) layers and the Tb22Fe70Co8 (at. %) films for the storage (ST) layers. In the five layered SiNx/NdTbFeCo/TbFeCo/SiNx/Al-Ti films, the Kerr rotation angles (θk) increased compared to those of the four layered films with either a mono-RO or a mono-ST layer at R (thickness ratio of ST to RO)≤3. The coercivity (Hc) significantly increased from 1.19 KOe-2.77 KOe to 2 KOe-5.6 KOe in an entire range of R. This was ascribed to an occurrence of the exchange-coupling between RO and ST layer. Squareness ratio monotonously increased from 0.75 to 1.0 as R increased from 1.5 to 6. The maximum carrier-to-noise ratio (CNR) of the five layered magneto-optical disk enhanced from 36.5 dB to 47.6 dB as R increased from 1.5 to 6. This was attributed to the improved Hc and the enhanced squareness due to the exchange-coupling. The composite of the experimental results suggests that thinner RO layer is favorable to obtain the high MO properties and the improved dynamic characteristics.

Enhancement of coercivity by underlayer control in Co/Pd and Co/Pt multilayers

Co/Pd and Co/Pt multilayers were sputtered on Pd or Pt underlayers and the effects of sputtering pressure during the formation of underlayers on the magnetic properties of multilayers were investigated. It was found that the coercivity of Co/Pd multilayers was strongly dependent on the sputtering pressure of underlayer and could be increased drastically from 1.2 kOe up to around 5 kOe merely by increasing the sputtering pressure of Pd underlayer from 6 mTorr to 24 mTorr, while in case of Co/Pt films, no significant change of the coercivity could be observed with the variation of sputtering pressure of the underlayer. For both multilayers, the magnetic reversal feature was affected by the surface roughness of the underlayer and multilayers grown on the underlayer with a rough surface favored a rotation dominated process. The Kerr rotation angle was found to be hardly affected by the preparation conditions of the underlayer.

Analysis of Scattering Light from Magnetic Material with Land/Groove by Three-Dimensional Boundary Element Method

A calculation method with three-dimensional Boundary Element Method (BEM) has been developed for analyzing scattering light from a magnetic material, in order to determine the contribution of land/groove shapes and incident beam polarization to Kerr rotation. A product of scattering beam intensity and the Kerr rotation angle (R·θk) has been calculated in the case that 680 nm wavelength Gaussian beam is focused on 680 nm or 1360 nm width land/groove, which has 85 nm depth or height. The land or groove shapes have been varied from rectangular shapes to V-shapes. Regardless of the land/groove shapes, the R·θk of lands is larger than that of grooves in TM-polarization and smaller in TE-polarization. The results in verification experiments well met the calculated ones, i.e., the carrier level of lands is higher than that of grooves in almost the entire range of recording frequency for TM-polarization light, and it is lower for TE-polarization.

PERPENDICULAR MAGNETIC ANISOTROPY AND MAGNETO-OPTICAL KEER PROPERTIES OF Co/(Pd-Au) METALLIC MULTILAYERS

We prepared Co/(Pd-Au) multilayers onto a glass substrates by rf magnetron sputtering at room temperature. Co/(Pd-Au) multilayers exhibit a magnetic easy axis perpendicular to the film plane up to a larger magnetic layer thickness than Co/Pd multilayer. Especially, Co/(Pd0.70Au0.30) multilayers became perpendicular at 33A. The magnetic anisotropy can be explained by the strain effect. The role of magnetoelastic energy due to the in-plane strain in the system is pointed out and discussed. We also investigated the magneto-optical(MO) polar Kerr effect of these multilayers. The polar Kerr rotation angle qk increases when the Au concentration is 4.5at% compared to Co/Pd multilayers, but decreases with increasing Au content.

Semiconductor laser resonator for magneto-optic floppy disk head

A basic reserch with a new method to detect magneto-optical signals using an external cavity laser diode is performed. The magneto-otical signal is detected as the frequency shift of a beat signal. Because of its simple structure and large frequency shift for small Kerr rotation angle, a highly sensitive optical head is possible.

Wavelength Modulations Of The Kerr-Rotation Angle For Pd/(Pt/Co/Pt) Modulated Multilayers Grown On Oxidized Si

Wavelength Modulations Of The Kerr-Rotation Angle For Pd/(Pt/Co/Pt) Modulated Multilayers Grown On Oxidized Si

Electronic theory for the nonlinear magneto-optical response of transition metals at surfaces and interfaces: Dependence of the Kerr rotation on the polarization and magnetic easy axis.

We extend our previous study of the polarization dependence of the nonlinear optical response to the case of magnetic surfaces and buried magnetic interfaces. We calculate for the longitudinal and polar configuration the nonlinear magneto-optical Kerr rotation angle. In particular, we show which tensor elements of the susceptibilities are involved in the enhancement of the Kerr rotation in nonlinear optics for different configurations and we demonstrate by a detailed analysis how the direction of the magnetization and thus the easy axis at surfaces and buried interfaces can be determined from the polarization dependence of the nonlinear magneto-optical response, since the nonlinear Kerr rotation is sensitive to the electromagnetic field components instead of merely the intensities. We also prove from the microscopic treatment of spin-orbit coupling that there is an intrinsic phase difference of 90$^{\circ }$ between tensor elements which are even or odd under magnetization reversal in contrast to linear magneto-optics. Finally, we compare our results with several experiments on Co/Cu films and on Co/Au and Fe/Cr multilayers. We conclude that the nonlinear magneto-optical Kerr-effect determines uniquely the magnetic structure and in particular the magnetic easy axis in films and at multilayer interfaces.

The properties of magneto-optical MnBiR (R=In, Ge, and Sn) thin films

The crystal structures and the magneto-optical properties of MnBiR (R=Ge, In, and Sn) thin films are reported. We found that doping MnBi films with Ge enhances their Kerr rotation angle θk(θk=2.1°, at λ=633 nm). It is thus possible to consider MnBi film doped with Ge a good candidate of magneto-optical recording material. In contrast, MnBi films doped with In or Sn loose the original NiAs-type hcp structure and correspondingly the Kerr rotation angle θk, is decreased.