Magneto-optical Kerr Effect Data Research Articles

Imaging Magnetization Switching Induced by Spin-Orbit Torque in Perpendicularly Magnetized Ta/CoFeB Structure

We report the study of current-induced magnetization switching in the Ta/CoFeB heterostructures by simultaneous magneto-electrical transport and magneto-optical Kerr effect (MOKE) microscopy measurements. Although the anomalous Hall hysteresis loop summarizes the general switching behaviors, the supplementary MOKE data can provide spatial and temporal information to visualize the magnetic domain evolution as functions of the applied current and the in-plane magnetic field. More importantly, when the initial magnetic field is not sufficient enough, the interfacial Dzyaloshinskii–Moriya interaction (DMI) would modulate the spin-orbit torque (SOT) current switching dynamics and lead to the formation of the intermediate Hall resistance plateau with meta-stable tilted domain texture. Our work elucidates the importance of the applied in-plane field and unveils an effective approach to investigate the SOT/DMI-related phenomena in symmetry-breaking magnetic heterostructures.

Correlating the Nanoscale Structural, Magnetic, and Magneto-Transport Properties in SrRuO3-Based Perovskite Thin Films: Implications for Oxide Skyrmion Devices

We investigated the structural and magnetic properties of bare SrRuO3 (SRO) ultrathin films and SrRuO3/SrIrO3/SrZrO3 (SRO/SIO/SZO: RIZ) trilayer heterostructures between 10 and 80 K, by comparing macroscopic data using the magneto-optical Kerr effect (MOKE) and magneto-transport (anomalous Hall effect: AHE), with nanoscale fingerprints when applying noncontact scanning force microscopy (nc-SFM) and magnetic force microscopy (MFM). SRO and RIZ ultrathin films were epitaxially grown at 650 °C onto vicinal SrTiO3 (100) single-crystalline substrates to a nominal thickness of 4 and 4/2/2 unit cells (uc), respectively. Our correlated analysis allows associating topographic sample features of overgrown individual layers to their residual magnetization, as is shown here to be relevant for interpreting the macroscopic AHE data. Although the hump-like features in the AHE suggest a magnetically textured skyrmion phase to exist around 55 K associated with the topological Hall effect (THE), both our MOKE and MFM data ...

What is the longitudinal magneto-optical Kerr effect?

We explore the commonly used classification scheme for the magneto-optical Kerr effect (MOKE), which essentially utilizes a dual definition based simultaneously on the Cartesian coordinate components of the magnetization vector with respect to the plane of incidence reference frame and specific elements of the reflection matrix, which describes light reflection from a ferromagnetic surface. We find that an unambiguous correspondence in between reflection matrix elements and magnetization components is valid only in special cases, while in more general cases, it leads to inconsistencies due to an intermixing of the presumed separate effects of longitudinal, transverse and polar MOKE. As an example, we investigate in this work both theoretically and experimentally a material that possesses anisotropic magneto-optical properties in accordance with its crystal symmetry. The derived equations, which specifically predict a so-far unknown polarization effect for the transverse magnetization component, are confirmed by detailed experiments on epitaxial hcp Co films. The results indicate that magneto-optical anisotropy causes significant deviations from the commonly employed MOKE data interpretation. Our work addresses the associated anomalies, provides a suitable analysis route for reliable MOKE magnetometry procedures, and proposes a revised MOKE terminology scheme.

Co-Ir interface alloying induced by thermal annealing

Using angular resolved X-ray Photoelectron Spectroscopy (XPS), Magneto Optic Kerr Effect (MOKE) and X-ray Absorption Spectroscopy (XAS), we characterize the structural and magnetic evolution upon annealing of two thin Co films (8 and 9 Monolayers) deposited on Ir(111). The XAS data collected in the near Co K edge region (XANES), interpreted with ab-initio simulations, show that intermixing takes place at the Co-Ir interface. Using a linear combination analysis, we follow the intermixing during the thermally driven diffusion process. At 500 °C, the interface between Co and Ir(111) roughens slightly, but no alloy formation is detected. At 600 °C, the Co film loses integrity and MOKE data show a rearrangement of the magnetic domains. Annealing to higher temperatures results in CoxIr1 − x alloy formation and Ir segregation on the surface.

Static and dynamic magnetic properties of Ni80Fe20anti-ring nanostructures

The static and dynamic behavior of Ni${}_{80}$Fe${}_{20}$ anti-ring arrays has been systematically investigated using broadband ferromagnetic resonance (FMR) spectroscopy, magneto-optical Kerr effect (MOKE), and magnetic force microscopy (MFM). The unit cell of this periodic lattice represents a hole in a continuous film, with an elliptical nanodot placed in the middle of the hole. The FMR responses display multiple absorption peaks due to the superposition of the absorptions from the anti-dot and the central nanomagnet (dot) regions of the anti-ring structures. Interestingly, for fixed anti-ring geometry, the static and dynamic behavior is markedly sensitive to the thickness of the structure due to complicated spatial distributions of the demagnetizing field. Direct MFM imaging reveals that at remanence, the central nanomagnets are in a single-domain state, for small sample thicknesses, whereas for larger thicknesses, they display a multidomain or vortex state. This observation is in good agreement with both FMR and MOKE data. All our results agree well with micromagnetic simulations.

Magneto-optical Kerr effect measurements on highly ordered nanomagnet arrays

In magnetic nanostructures, anisotropy directly influences formation of domains and their evolution with external field. Magneto-optic Kerr effect (MOKE) was used to study samples fabricated by templated electrodeposition of Cobalt into anodic aluminum oxide (AAO) templates. With proper conditions, both Co solid nanowire, as well as hollow nanotubule arrays, were formed. The morphology of the samples was investigated using SEM and AFM. Since as-deposited samples have high surface roughness, chemical mechanical polishing was used to polish the samples to achieve an optically flat surface. MOKE data show that shape anisotropy dominates along the long dimension and interaction effects between nanowires are important. A marked difference is seen between solid nanowires and hollow nanotubule samples, the latter showing formation of vortices.

Magnetic anisotropy of Co2MnSn1−xSbx thin films grown on GaAs (001)

Heusler alloy Co2MnSn1−xSbx (x=0.0, 0.5, and 1.0) thin films were grown on GaAs (001) substrates using pulsed laser deposition techniques. Growth parameters have been determined that result in highly magnetically anisotropic, crystalline, and oriented (001) films. The angular dependences, relative to the GaAs (001) crystallographic directions, of the coercive field Hc(θ) and the remanence Mr(θ) were determined from angle dependent magneto-optic Kerr effect (MOKE) measurements. It was found that Hc(θ) revealed higher order symmetry contributions to the magnetic anisotropy than did Mr(θ). The Fourier analysis of rotational MOKE data was used to determine the symmetry contributions to the total anisotropy.

Magnetization reversal via symmetric rotation of layers in exchange biased multilayers

We have investigated the magnetization reversal for exchange coupled polycrystalline [IrMn∕CoFe]N multilayers. Polarized neutron reflectivity (PNR) data indicate a simultaneous coherent rotation of all ferromagnetic layers for a sample with N=10 and angles of 45° and 90° between the applied field and the exchange bias direction. On the other hand, magneto-optic Kerr effect (MOKE) measurements, which are sensitive mainly to the two topmost bilayers, reveal a variation of the strength of the exchange bias and the uniaxial anisotropy as a function of N for multilayers with N=1 up to 10. The MOKE data thus indicate the direction of the magnetization to vary from layer to layer for intermediate fields. PNR was found to be insensitive to this variation as the deviation of the layer magnetization directions from its mean value is relatively small (≈10°). These studies demonstrate how the complementary techniques PNR and MOKE can be used to obtain a layer-by-layer vector magnetometry of multilayer stacks.

Temperature-dependent magnetism of Fe thin films on ZnSe(0 0 1)

We present X-ray magnetic circular dichroism (XMCD) and magneto-optical Kerr effect (MOKE) data on the magnetic properties of Fe/ZnSe(0 0 1) thin films at increasing Fe coverage. The magnetic behaviour of the Fe overlayer is superparamagnetic for a coverage up to 6 monolayers whereas, above this threshold, a truly ferromagnetic phase shows up. XMCD and MOKE data show that this behaviour is substantially unchanged in the temperature range 10–300 K for all the investigated coverages: these findings imply that the blocking temperature is definitely below 10 K.

Evidence of native oxides on the capping and substrate of Permalloy gratings by magneto-optical spectroscopy in the zeroth- and first-diffraction orders

Magneto-optical Kerr effect (MOKE) spectroscopy in the zeroth- and first-diffraction orders at polar magnetization is applied to Permalloy wire gratings deposited on Si substrates and protected by Cr capping. The experimental MOKE data are compared with data simulated using the local modes method. The extensive simulations of the MOKE spectroscopic parameters exhibit significant sensitivity to t(Cr2O3) and t(SiO2), the thicknesses of native oxide layers developed on the capping and the substrate, respectively. The approach may be useful for monitoring the basic micromagnetic properties of small elements with nanometer-scale resolution, as well as for monitoring the deposition processes and aging of magnetic nanostructures in magnetic recording and magnetic random access memory technologies.

Magneto-optic Kerr effect investigation of cobalt and permalloy nanoscale dot arrays: Shape effects on magnetization reversal

Using the magneto-optic Kerr effect (MOKE) and magnetic force microscopy we have investigated the shape dependence of magnetization reversal in a series of cobalt and permalloy nanoscale dot arrays. The patterns were produced by e-beam lithography combined with e-beam deposition and lift-off techniques. To avoid pattern to pattern variations in growth-induced anisotropy and or thickness, elliptical elements of varying aspect ratio were deposited simultaneously on a single substrate. All arrays were 1.0×2.5 μm tetragonal lattices and were fabricated with 300 Å thickness of cobalt and with 200 and 300 Å thickness of permalloy. From MOKE data we extract the field at which the onset of switching occurs for each array. For each material (viz. Co or permalloy), and thickness (200 or 300 Å), the switching field versus aspect ratio can be interpreted by a single nucleation field. The dependence of the nucleation barrier on the material and its thickness is discussed.

Anisotropy of an ultrathin Cu(111)/Co(111)/Cu(111) wedge

An anisotropy study is reported on an ultrathin fccCu(111)/Co(111)/Cu(111) wedge grown on a sapphire substrate by molecular beam epitaxy. Roomtemperature polar and longitudinal magneto-optical Kerr effect (MOKE) measurements were analysed by twodifferent methods to determine the volume and surface contributions to theanisotropy. The values obtained by the `area method' by calculating thedifference in area between the in-plane and perpendicular magnetization curvesand also by simulation of the polar MOKE curves were not in agreement. The`area method' was found to be unreliable for analysing MOKE data. Values ofthe anisotropy obtained by simulation agreed with the expected bulk value forfcc Co of 0.0 MJ m-3 and the surface anisotropy was found to lie in the range0.4-0.5 mJ m-2.

Using magnetoresistance to investigate magnetic interface anisotropy

The ability to grow high quality thin metallic layers has brought about the discovery of the giant magnetoresistance (GMR) in multilayers and equally the perpendicular anisotropy exhibited by certain ferromagnetic thin films such as Co. In this article, we will describe magnetoresistance and magneto-optical Kerr effect (MOKE) measurements of molecular beam epitaxy-grown multilayers of Co/Cu(111). It is demonstrated that by controlled doping of the interface between the Co and Cu with submonolayer amounts of Au we are able to increase the magnitude of the GMR. Analysis of MOKE data shows that there is an increase in the perpendicular anisotropy of the Au-doped samples compared to those without Au which can account for the increase in the GMR.

High current density self-field effects and low-frequency noise in NiFe/Ag GMR multilayers

High current densities (10/sup 6/-10/sup 7/ A/cm/sup 2/) produce magnetic fields which can induce antiparallel magnetic alignment in large (16 /spl mu/m and 8 /spl mu/m) NiFe/Ag thin film multilayer devices. We induce GMR in unannealed devices which normally do not display GMR. We find multiple peaks in the magnetoresistance curves of annealed and unannealed devices. Analysis of the positions and shapes of these magnetoresistance peaks provides a new set of tools for determining the micromagnetic structure of the multilayers. Our magneto-optical Kerr effect data and low frequency noise data correlate with the magnetoresistance peaks and may yield further information about layer-layer interactions and domain structure.

Nonlinear and linear Kerr studies of [formula omitted] multilayers

Magnetization induced optical second harmonic generation (MSHG) in combination with the magneto-optical Kerr effect (MOKE) was used to study thin Co films and Cu Co multilayers of thicknesses between 1 and 20 monolayers (ML) grown on a Cu(001) substrate. From the different dependence of MSHG and MOKE on Co film thickness we get direct information about the interface sensitivity of MSHG. Modifying the vacuum Co interface by gas adsorption yields the relative contributions of the vacuum Co and the Co Cu(001)- substrate interfaces. Both MSHG and MOKE data can be accurately described by a multiple reflection model.