Longitudinal Magneto-optical Kerr Effect Research Articles

Giant magneto-optical Kerr effects governed by the quasi-bound states in the continuum

The magneto-optical Kerr effect (MOKE), as one of the magneto-optical effects, exhibits polarization change upon reflection that can be used to explore the internal information of magnetic materials with broad applications in modern information technology. However, typically, MOKE is quite weak due to the lower magneto-optical interaction. To tremendously enhance the MOKE, quasi-bound states in the continuum in a one-dimensional Ce- doped Y3Fe5O12 (CeYIG) film photonic crystal slabs (PCS) are proposed to improve the magneto-optical interaction in this work. A giant enhancement in the rotation angle and ellipticity of the longitudinal MOKE, which is about 93.4 and 136.8 times stronger than a pure uniform CeYIG, can be realized. Almost circularly polarized reflected beams with different chiralities are obtained with the CeYIG film. By tuning the geometric parameters of the PCS and the applied external magnetic field, dynamic control of polarization states of the reflected beams with different wavelengths can be realized. This magneto-optical metasurface provides a convenient way for the implementation of magneto-optical devices such as information memory devices, sensors, polarizers, and chiral devices.

Hysteresis of magnetization statics and dynamics in [Pt/Co] multilayer

The magnetic multilayer of Co separated by thin spacer layer of Pt was deposited by DC-magnetron sputtering. From the longitudinal magneto-optical Kerr effect based magnetometry and microscopy as well as magnetic force microscopy, the hybrid magnetization structure was deduced: the large size, micrometer scale magnetic domains with in-plane “core magnetization” patterned by nanometer scale domains with out-of-plane components. The hysteresis as a function of in-plane applied magnetic field of both: (i) magnetization curve measured by Superconducting Quantum Interference Device and (ii) dynamic responses measured by broadband Vector Network Analyzer spectroscopy were observed. The experimental results are well described by micromagnetic simulations. These magnetic history dependent effects were explained by magnetization cores, with in plane component, switching.

Longitudinal magneto-optical Kerr effect in subwavelength thick ferromagnetic films investigated by Mueller matrix ellipsometry

Accurately characterizing the magneto-optical (MO) Kerr and optical responses of subwavelength thick ferromagnetic films is of great significance in the field of MO devices. In this paper, an in-situ characterization method based on the Mueller-matrix ellipsometry in a longitudinal MOKE configuration has been proposed, with which the longitudinal MO Kerr effects phenomenon occurring in the sub-wavelength thick ferromagnetic films can be thoroughly investigated. We establish an analytical representation of the MO Kerr responses by simplifying the transfer-matrix model using a more appropriate constraint about the film thickness. By virtue of the high repeatability precision of the measured Mueller matrix better than 0.0002, the MO Kerr response signal of the ferromagnetic films with thicknesses far from the ultra-thin limit 2π|N|∙d/λ<<1 can be reliably captured, despite the well-known weak signal amplitudes. The MO coupling constant, the Kerr ellipticities and rotations can be further determined from the measured Mueller matrix. Experimental results on the Ni and NiFe2O4 films with thicknesses less than 100 nm demonstrate the proposed characterization approach based on the Mueller matrix ellipsometry as a practical and precise technique. As the film thickness increases to larger than the ultrathin film threshold, the proposed method can provide more reasonable characterization results, and the influence of film thickness on the MO responses can be more accurately evaluated.

Hydrogenation Effect on Interlayer Coupling and Magneto-Transport Properties of Pd/Co/Mg/Fe Multilayers.

Hydrogenation-induced modification of magnetic properties has been widely studied. A Mg spacer layer with high hydrogen storage stability was clamped in a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and explore the structure's magneto-transport properties. After 1 bar hydrogen exposure, the formation of a stable MgH2 phase was demonstrated in an ambient environment at room temperature through X-ray diffraction. Lower magnetic coupling and enhanced magnetoresistance, compared to those of the as-grown sample, were observed using the longitudinal magneto-optical Kerr effect and a four-probe measurement. In this study, the hydrogenation stability of ferromagnetic multilayers was improved, and the concept of a hydrogenation-based spintronic device was developed.

Exchange Bias and Vertical Magnetic Shift on Co−CoO Thin Films

AbstractThis work reports the results of an experimental study on Si(001)/Au(111)/Co/CoO/ZrO2 elaborated by electron beam evaporation. The chemical composition of the oxidized state of cobalt and zirconium cover layers derived from metallic deposition is confirmed by X‐ray photoelectron spectroscopy (XPS). Magnetic properties are probed by magneto‐optical Kerr effect (MOKE). The polar magneto‐optic Kerr effect (PMOKE) measurements reveal that the cooling at 77 K under an applied magnetic field induces an exchange coupling which is manifested by a positive exchange bias (EB) field accompanied by a negative vertical shift of the magnetization. In longitudinal magneto‐optical Kerr effect (LMOKE), the exchange coupling depends on the orientation of the applied measuring magnetic field. It is found that both the exchange field shift rate hshift and the vertical shift rate in magnetization mshift exhibit a peak at 45° between the applied field and the [100] in‐plane direction which may be associated with the presence of uncompensated pinned spins at the Co−CoO interface.

Annealing dependence on magnetization dynamics and two-magnon scattering in Co40Fe40B20 thin films

Investigation of magnetization dynamics of low-damping ferromagnetic layers is of paramount interest for the realization of spin-based electronic devices. Here, we report the effect of surface oxidation on the structural properties, magnetization reversal and spin dynamics of Co40Fe40B20 (CFB) films. X-Ray diffraction results show that both as-deposited and annealed CFB layers up to 250 °C exhibit an amorphous state. Partial crystallization of CoFe is observed in CFB films above 350 °C. Magnetization reversal curves measured using longitudinal magneto-optic Kerr effect indicate a characteristic square loop along the easy axis for all samples. Ferromagnetic resonance (FMR) results show that the resonance field (Hr) shifts due to changes in the structural phase or microstructure. FMR linewidth (ΔH) is linear for both as-deposited and all annealed CFB above 10 GHz, whereas anomalous behaviour in ΔH as a function of frequency is observed below 10 GHz frequency for annealed thin films. The extracted damping parameter manifests extrinsic contributions in the annealed samples compared to the as-deposited. Angular-dependant FMR results show ΔH and Hr exhibit opposite trends in CFB film annealed at 450 °C due to the presence of inhomogeneities. It suggests the signature of two-magnon scattering in the 450 °C annealed CFB. Our systematic study helps in the understanding of the effect of annealing on the crystallinity and magnetization dynamics in CFB thin films.

Evidence for vortex state in Fe2CoGe thin films using FORC and magnetic imaging

We report on the evidence for the vortex state in the thin films of Fe2CoGe through first order reversal curves, magnetic force microscope, longitudinal magneto-optical Kerr effect and micro-magnetic simulations. Phase purity of the films confirmed through X-ray diffraction, which confirms the A2 type disorder Heusler alloy structure. Contour graph of first order reversal curves infers the formation of vortex state that is useful to understand magnetization reversal and switching process. We do observe the vortex state ∼1 μm with in – plane curling of the magnetization using magnetic force microscope phase analysis. We believe that realization of vortex state formation in Fe2CoGe thin films may cater applications in future magnetic data storage and microwave oscillators.

Epitaxial growth of high quality Mn3Sn thin films by pulsed laser deposition

Noncollinear antiferromagnet Weyl semimetal Mn3Sn has recently attracted great research interest. Although large anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and magneto-optical effect have been observed in Mn3Sn, most studies are based on single crystals. So far, it is still challenging to grow high quality epitaxial Mn3Sn thin films with transport and optical properties comparable to their single crystal counterparts. Here, we report the structure and magneto-optical and transport properties of epitaxial Mn3Sn thin films fabricated by pulsed laser deposition (PLD). Highly oriented Mn3+xSn1−x (0001) and (112¯0) epitaxial films are growth on single crystalline Al2O3 and MgO substrates. Large anomalous Hall effect up to ΔρH=3.02 μΩ cm and longitudinal magneto-optical Kerr effect with |θK| = 38.1 mdeg at 633 nm wavelength are measured at 300 K, which are comparable to Mn3Sn single crystals. Our work demonstrates that high quality Mn3Sn epitaxial thin films can be fabricated by PLD, paving the way for future device applications.

Impact of Argon working pressure on the magnetic properties of sputtered Co60Fe20B20 thin films

We present thorough investigation of the influence of Argon gas working pressure (PAr) on Co60Fe20B20 (CFB) thin films deposited on Si. The longitudinal magneto-optic Kerr effect measurements indicate that all films exhibit uniaxial anisotropy caused by the self-steering effect arising due to the oblique angle deposition. The coercive field is found to be sensitive to PAr during growth and reached to a minimal value of 0.766 kA/m at 0.147 Pa. The ferromagnetic resonance measurements revealed that PAr has a direct impact on the inhomogeneous linewidth, anisotropy, and the effective Gilbert damping constant (αeff). The low value of αeff ∼(4.16±0.10)×10−3is achieved in film grown at PAr∼0.147 Pa with negligible inhomogeneity and low anisotropy. At this optimum value of PAr, the surface roughness of the films is found to be lowest (∼ 4 Å). The observed changes in the static and dynamic magnetization properties in these CFB films on varying the PAr are correlated to the growth-rate-dependent changes in internal stress in the film. The choice of the value of PAr employed during sputtering of CFB films at room temperature is thus demonstrated as the simple control parameter for tuning its structural and magnetic properties for the development of spintronic memory applications.

Large exchange bias and spin pumping in ultrathin IrMn/Co system for spintronic device applications

Few nanometers thick antiferromagnetic/Ferromagnetic bilayer based spintronic devices have emerged as a potential nanostructured bilayer for achieving ultrahigh-speed magnetization switching, low power dissipation, terahertz magnetization dynamics, and are compatible with CMOS technology. The systematic investigation of the exchange bias (EB) in the Ir22Mn78/Co system is performed by varying Co thickness (tCo) in the range of 6–20 nm with 10 nm thin Ir22Mn78 layer on top, using longitudinal magneto-optic Kerr effect (L-MOKE) and ferromagnetic resonance (FMR) measurements at room temperature. Here, we report the occurrence of a record high EB field in this bilayer system, which is 13.11 mT (9.04 mT) statically (dynamically) for 6 nm thick of Co. The percentage change of 313.5 % (251.7%) in exchange bias field is found through FMR (MOKE) measurements with respect to tCo variation from 20 to 6 nm. Additionally, the spin pumping mechanism is also studied in the above stated material system by using the FMR technique. The observed linear dependence of effective Gilbert’s damping with respect to the 1/tCo, indicates the occurrence of spin pumping phenomena. The study suggests that tunability of both the exchange interaction and spin pumping behavior in this Ir22Mn78/Co system, makes this system suitable for future antiferromagnetic spintronic devices.

Magnetic anisotropy and reversal in epitaxial FeGa/IrMn bilayers with different orientations of exchange bias

Epitaxial FeGa/IrMn bilayers with exchange biases along the FeGa[100] and [110] directions are prepared on MgO(001) single crystal substrates by magnetron sputtering through controlling the orientation of the external field &lt;i&gt;in situ&lt;/i&gt; applied during growth. The effect of the exchange bias orientation on the magnetic switching process and the magnetic switching field are studied. The X-ray &lt;i&gt;φ&lt;/i&gt;-scan indicates that the FeGa layer is epitaxially grown with a 45° in-plane rotation on the MgO(001) substrate along the FeGa(001)[110] direction and the MgO(001)[100] direction. The measurements of the angular dependence of the ferromagnetic resonance field and the corresponding fitting to the Kittel equation show that the samples have a superposition of fourfold symmetric magnetocrystalline anisotropy &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {K}_{1} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, unidirectional magnetic exchange bias anisotropy &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M5.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, and uniaxial magnetic anisotropy &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ {K}_{\mathrm{u}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; with configuration of &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; or &lt;inline-formula&gt;&lt;tex-math id="M8"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M8.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. The combined longitudinal and transverse magneto-optical Kerr effect measurements show that sample with &lt;inline-formula&gt;&lt;tex-math id="M9"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[100\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M9.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; exhibits square loops, asymmetrically shaped loops, and one-sided two-step loops in different external magnetic field directions. In contrast, the sample with &lt;inline-formula&gt;&lt;tex-math id="M10"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}}//\left[110\right] $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M10.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; exhibits one-sided two-step and two-sided two-step loops as the magnetic field orientation changes. Because the &lt;inline-formula&gt;&lt;tex-math id="M11"&gt;\begin{document}$ {K}_{1} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M11.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; is superimposed by &lt;inline-formula&gt;&lt;tex-math id="M12"&gt;\begin{document}$ {K}_{\mathrm{u}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M12.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and &lt;inline-formula&gt;&lt;tex-math id="M13"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M13.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, the in-plane fourfold symmetry of the magnetic anisotropy energy is broken. The local minima are no longer strictly along the in-plane &lt;inline-formula&gt;&lt;tex-math id="M14"&gt;\begin{document}$ \left\langle{100}\right\rangle $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M14.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; directions, but make a deviation angle which depends on the relative orientation and strength of magnetic anisotropy. A model based on the domain wall nucleation and propagation is proposed with considering the different orientations of &lt;inline-formula&gt;&lt;tex-math id="M15"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M15.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, which can nicely explain the change of the magnetic switching route with the magnetic field orientation and fit the angular dependence of the magnetic switching fields, indicating a significant change of domain wall nucleation energy as the orientation of &lt;inline-formula&gt;&lt;tex-math id="M16"&gt;\begin{document}$ {K}_{\mathrm{e}\mathrm{b}} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20220166_M16.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; changes.

Independent control of the longitudinal magneto-optical Kerr effect and its refractive index sensing in Ag-Co composite nanogratings

Conventionally, tuning magneto-optical Kerr rotation via the excitation of surface plasmons (SPs) usually results in extremely low light energy at the Kerr null point position in the optical spectrum. Realizing independent control of the magneto-optical effect is considered as an effective solution. The decoupling between the Kerr effect and optical response is achieved in our constructed Ag/Co composite nanogratings, and the Kerr rotation used as the refractive index sensing signal can be obtained without SP excitation. The refractive index sensing performance is improved by reducing electron collision frequency in Ag/Co nanogratings and the figure of merit reaches 96/RIU, far exceeding that of Co nanogratings.

A UHV MOKE magnetometer complementing XMCD-PEEM at the Elettra Synchrotron

We report on a custom-built UHV-compatible Magneto-Optical Kerr Effect (MOKE) magnetometer for applications in surface and materials sciences, operating in tandem with the PhotoEmission Electron Microscope (PEEM) endstation at the Nanospectroscopy beamline of the Elettra synchrotron. The magnetometer features a liquid-nitrogen-cooled electromagnet that is fully compatible with UHV operation and produces magnetic fields up to about 140 mT at the sample. Longitudinal and polar MOKE measurement geometries are realized. The magneto-optical detection is based on polarization analysis using a photoelastic modulator. The sample manipulation system is fully compatible with that of the PEEM, making it possible to exchange samples with the beamline endstation, where complementary X-ray imaging and spectroscopy techniques are available. The magnetometer performance is illustrated by experiments on cobalt ultra-thin films, demonstrating close to monolayer sensitivity. The advantages of combining in situ growth, X-ray Magnetic Circular Dichroism imaging (XMCD-PEEM) and MOKE magnetometry into a versatile multitechnique facility are highlighted.

Interface-driven magnetic anisotropy of epitaxial [formula omitted] thin films

The effect of film-substrate interface on the magnetic anisotropy (MA) of epitaxial Fe4N thin films grown on single crystalline MgO (100) and MgO (111) substrates has been studied in this work. Both samples were grown simultaneously using a reactive dc magnetron sputtering process at a substrate temperature of 250°C. Single phase Fe4N samples were found to grow epitaxially on (100) and (111) oriented MgO substrates as confirmed from out-of-plane x-ray diffraction and in-plane ϕ-scan measurements. The MA of (100) and (111) oriented Fe4N samples was measured using longitudinal magneto-optical Kerr effect (MOKE). In spite of being grown simultaneously, the MA of both these samples was found to be different. Secondary ion mass spectroscopy and x-ray reflectivity measurements revealed the formation of a dense layer at the film-substrate interface. The MA of this dense layer along with the MA of Fe4N has a dramatic effect on magnetic reversal depending on the orientation of the substrate. Further, from the MOKE measurements, the difference in the magnetization switching processes was found to depend on the microstructure and orientation of Fe4N thin films.

Study of magneto-optical activity in cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films

The study of magneto-optical (MO) properties is reported in epitaxial cerium (Ce) substituted yttrium iron garnet thin films deposited on Gd3Ga5O12 (GGG) substrates using pulsed laser deposition technique at (i) different O2 partial pressure (OPP) during film deposition and (ii) with different film thickness at a given OPP. The MO activity is estimated by measuring the Kerr rotation using the longitudinal magneto-optical Kerr effect with blue (405 nm), green (532 nm), and red (632 nm) incident laser light. The Kerr rotation is observed to increase with an increase in OPP and vary differently with thickness for a given OPP as a function of incident light wavelength. The results are explained in terms of the possible charge transfer mechanism for the films prepared with OPP variation and the optical interference effects in dielectric films with thickness variation.

Study of magnetic nanowires of amorphous Co20Fe60B20 prepared by oblique angle deposition on nanorippled substrate

An array of magnetic nanowires of amorphous Co20Fe60B20 alloy has been prepared by oblique angle deposition of material on nanorippled substrate. The angle of incidence is chosen such that the deposition takes place on only one facet of the nanoripples. Grazing incidence small angle x-ray scattering measurement has been done in order to characterize the morphology of the nanowires. It is found that the oblique angle deposition results in columnar growth, and each individual nanowire consists of nanocolumns having average diameter of 7 nm and a tilt angle of 37° with respect to the surface normal. Azimuthal angle dependence of longitudinal magneto-optical Kerr effect measurement shows that the nanowires possess a well-defined uniaxial magnetic anisotropy with the easy axis of magnetization tilted by an angle of 25° with respect to the direction of the ripples. The magnetization follows the Stoner-Wohlfarth model with a very narrow distribution in the direction of easy axis. It is suggested that, tilt of the easy axis can be understood in terms of the interplay of two shape anisotropy terms corresponding to the ensemble of strongly interacting nanocolumns through magnetostatic dipolar interaction, and the overall shape of a nanowire.

Magnetic textures in hemispherical thin film caps with in-plane exchange bias

Hemispherical caps of in-plane exchange biased IrMn/CoFe layer systems have been fabricated on top of regularly arranged spherical silica particles by magnetron sputtering, creating magnetic Janus particles. In this thin film layer system cap, the magnetic shape anisotropy of the topographically non-flat hemispheres competes with the unidirectional anisotropy induced by the exchange bias. The magnetic properties of this non-trivial system have been investigated by longitudinal magneto-optical Kerr effect magnetometry, where a characterization method has been developed considering both the curved layer system and the signal contributions of flat parts of the sputtered thin film system. Both remagnetization curves, from Kerr magnetometry and the magnetic force microscopy images, reveal an onion state in the magnetic caps of the ensemble. Additional micromagnetic simulations show a stabilization of the onion state due to the introduced unidirectional anisotropy also in individual hollow hemispheres as compared to the vortex state exhibited by purely ferromagnetic caps.

Thickness dependent domain wall dynamics in Fe2CoSi thin films

We report on the effect of thickness on the magnetic properties and domain wall motion in as deposited Fe2CoSi thin films. Reflections present in selected area electron diffraction (SAED) micrograph infer that they are allowed reflections and are related to the Fe2CoSi. The coercivity is found to increase with the film thickness and the same is explained on the basis of Néel domain wall model. Longitudinal magneto-optical Kerr effect (L – MOKE) infers that the formation of ripple kind of domains that depend on the orientation of the field. L – MOKE data also infers nearly perfect 4-fold anisotropy for the film with thickness 5 nm and a weaker 4-fold anisotropy at higher thicknesses. Up on varying the angle between magnetic field and the film edge to 0° or 90°, indeed there is a transformation of the film magnetization from easy direction to hard direction. Fast Fourier transform of magnetic force microscopy (MFM) and polar plots infer a uniaxial anisotropy and a four-fold anisotropy in the films. Micromagnetic simulations infer that the coercivity value depends on the void size and enhances up to certain radius, above which it decreases. Present results would indeed be helpful for the future spintronic applications.

Comparison of high temperature growth versus post-deposition in situ annealing in attaining very low Gilbert damping in sputtered Co2FeAl Heusler alloy films

In this work, a detail study on the effectiveness of high substrate temperature (TS) during deposition versus in situ annealing of the films at high temperature (TA) after sputtering at room-temperature is compared with an objective to obtain Heusler alloy thin films of Co2FeAl (CFA) having optimally low αint (with an upper bound of 1.75 × 10-3) and 12–17% smaller MS by employing ion beam sputtering technique and Si(100) as substrates for current induced magnetization switching application. In each of the two series of CFA films, prepared with different choice of TS and TA (lying in 300–773 K range) were explored for optimally tailoring their structural, static and dynamic magnetization properties. Structural study revealed that although all the CFA films were polycrystalline but the post-deposition annealed films were structurally optimal with higher density (6.36 ± 0.09 g/cm3) and lower interface roughness (0.48 ± 0.03 nm) compared to the CFA films grown at high TS (6.23 ± 0.06 g/cm3, 0.61 ± 0.01 nm). In plane field-angle dependent longitudinal magneto optical Kerr effect (L-MOKE) study revealed the existence of a coupling between the weak uniaxial and biaxial magnetic anisotropies present in these films, attributed to the employed deposition geometry. Ferromagnetic resonance (FMR) spectroscopy measurements, performed in both the geometries - in-plane as well as out of plane, revealed a lowest value of 1.19 (±0.08) × 10-3 of αint in the film post-annealed at 773 K. In addition, the observed non-linear relation between the αint and the dynamical ‘g’-factor suggests that the contribution of spin orbit interaction to the damping is far less compared to the damping contribution from the DOS present near the Fermi level. It is remarkable to note that the as-grown CFA films sputtered at room temperature exhibited a record lowest value of 1.73 (±0.09) × 10-3 of αint. Attainment of such small value of Gilbert damping and having moderate magnetization in high spin polarized Co2FeAl Heusler films sputtered on the Si (100) substrate opens up their great application potential in future spintronics devices.

An integrated ultra-high vacuum apparatus for growth and in situ characterization of complex materials.

Here, we present an integrated ultra-high vacuum apparatus-named MBE-Cluster -dedicated to the growth and in situ structural, spectroscopic, and magnetic characterization of complex materials. Molecular Beam Epitaxy (MBE) growth of metal oxides, e.g., manganites, and deposition of the patterned metallic layers can be fabricated and in situ characterized by reflection high-energy electron diffraction, low-energy electron diffraction, Auger electron spectroscopy, x-ray photoemission spectroscopy, and azimuthal longitudinal magneto-optic Kerr effect. The temperature can be controlled in the range from 5 K to 580 K, with the possibility of application of magnetic fields H up to ±7 kOe and electric fields E for voltages up to ±500 V. The MBE-Cluster operates for in-house research as well as user facility in combination with the APE beamlines at Sincrotrone-Trieste and the high harmonic generator facility for time-resolved spectroscopy.