Longitude magneto optical Kerr effect of Fe/GaAs (0 0 1) with Al overlayers

The longitude magneto optical Kerr effect (LMOKE) is investigated on ultrathin Fe film grown on GaAs (0 0 1) substrate with Al overlayer. The formula of the longitude magneto optical Kerr effect is derived to find out the influence of the Al overlayer on the magneto optical properties of Fe/GaAs (0 0 1) sample. Results obtained from this formula fit very well with the experimental data. The change of the Kerr rotation as a function of the incident angle is also given, which can be used to find a proper angle in sample measurement. A numerical simulation was carried out to find out the relation between Kerr rotation and optical properties of the overlayer. Results from this simulation can be used to select the best overlayer material to protect the Fe/GaAs (0 0 1) sample.     

Influence of V and Mo overlayer on magneto-optical Kerr effect in ultrathin Co films

A method for characterization of sub-nanometer thick Co/V and Co/Mo interfaces is proposed that uses magneto-optical ellipsometry. Both the polar Kerr rotation and ellipticity are fitted simultaneously to different models of interface layer. The magneto-optical data are measured for varying thicknesses of the cobalt layer and overlayer by scanning of a laser beam over the samples with two orthogonal wedges. Decrease of magneto-optical effect at both interfaces Co/V and Co/Mo were observed, which corresponds to interface layers of thicknesses ranging from one to two monoatomic layers. In the case of vanadium, the interface layer is sharper and can be explained either by reduced magnetic moment of cobalt, or by anti-parallel magnetic moment of vanadium near the Co/V interface.     

SMOKE

Research activities associated with the surface magneto-optic Kerr effect (SMOKE) are reviewed. The purpose is to stimulate interest in the range of contemporary topics in surface magnetism and magneto-optics that SMOKE has addressed. These include the quest for monolayer magnetism, the nature of the surface magnetic anisotropy, trends in the Curie temperature with film thickness, and the critical magnetization exponent at the two-dimensional phase transition. Also, a macroscopic formalism that provides insights into magneto-optics in the ultrathin limit is examined and used to simulate the properties of a number of overlayer, sandwich and superlattice film configurations of interest. Comparisons are then made to experiment and the outlook for the future is examined.     

Magnetic proximity effects in antiferromagnet/ferromagnet bilayers: the impact on the Néel temperature

We present a study of the ordering temperature of an ultrathin antiferromagnetic film in the proximity of a ferromagnetic layer. The Néel temperature of a single-crystalline antiferromagnetic FexMn1-x film on Cu(001) in contact with a ferromagnetic Ni layer was monitored by the discontinuity in the coercivity as a function of temperature by magneto-optical Kerr effect measurements. It decreases by up to 60 K if the magnetization axis of the ferromagnet is switched from out of plane to in plane by deposition of a Co overlayer. These results give clear evidence for a magnetic proximity effect in which the ferromagnetic layer substantially influences the ordering temperature of the antiferromagnetic layer.     

Study of magnetization reversal and anisotropy of single crystalline ultrathin Fe/MgO(001) film by magneto-optic Kerr effect

The magnetization reversal process of Fe/MgO(001) thin film is investigated by combining transverse and longitudinal hysteresis loops. Owing to the competition between domain wall pinning energy and weak uniaxial magnetic anisotropy,the typical magnetization reversal process of Fe ultrathin film can take place via either an "l-jump" process near the easy axis, or a "2-jump" process near the hard axis, depending on the applied field orientation. Besides, the hysteresis loop presents strong asymmetry resulting from the variation of the detected light intensity due to the quadratic magneto-optic effect. Furthermore, we modify the detectable light intensity formula and simulate the hysteresis loops of the Kerr signal. The results show that they are in good agreement with the experimental data.     

MOKE hysteresis loop method of determining the anisotropy constants of ferromagnetic thin films: fe on GaAs(1 0 0) with overlayers of Au and Cr

This paper presents a quantitative method used to determine the magnetocrystalline anisotropy constants of thin magnetic films from normalized magnetization data measured on a magneto-optic Kerr effect (MOKE) magnetometer. The method is based on a total magnetic energy density model, and incorporates higher order effects in the detected signal. By way of illustration, the method is used to determine the magnetocrystalline anisotropy constants of epitaxial thin Fe films on GaAs substrates, which have different overlayers. It is shown that a Cr overlayer on a 30 ML thick Fe film reduces the uniaxial contribution to the magnetic anisotropy compared with an Au overlayer.     

Modes of periodic domain wall motion in ultrathin ferromagnetic layers

Magnetization reversal in a periodic magnetic field is studied on an ultrathin, ultrasoft ferromagnetic Pt/Co(0.5 nm)/Pt trilayer exhibiting weak random domain wall (DW) pinning. The DW motion is imaged by polar magneto-optic Kerr effect microscopy and monitored by superconducting quantum interference device susceptometry. In close agreement with model predictions, the complex linear ac susceptibility corroborates the dynamic DW modes segmental relaxation, creep, slide, and switching.     

Oxygen adsorption on ultrathin Co/Ir(1 1 1) films: Compositional anomaly

Adsorption of oxygen on ultrathin Co/Ir(1 1 1) films thinner than 4 monolayers in an ultrahigh vacuum environment was studied. For oxygen adsorption on cobalt films, the complex adsorption kinetics emerges partly due to the incorporation of oxygen. The amount of oxygen adsorbed at the surfaces is higher than that incorporated into the film as revealed from sputter profiling measurements. At room temperature the CoO layer exhibits paramagnetism and could not contribute to the remanent Kerr intensity. As oxygen exposure increases, the reduction of the Kerr intensity is due to the reduction of the effective layer for the magnetic measurements. Compared with oxygen saturated cobalt films, the concentration of adsorbed oxygen per Co atom shows an oscillatory behavior. A compositional anomaly of a great amount of adsorbed oxygen in submonolayer Co coverage occurs because of the maximized number of adsorption and incorporation sites for oxygen on the surface. A larger charge transfer between Co and oxygen was observed for thinner Co overlayers as revealed from the larger chemical shifts of Auger lines.     

Application of longitudinal generalized magneto-optical ellipsometry in magnetic ultrathin films

The longitudinal generalized magneto-optical ellipsometry(GME) method is extended to the measurement of threelayer ultrathin magnetic films. In this work, the theory of the reflection matrix is introduced into the GME measurement to obtain the reflective matrix parameters of ultrathin multilayer magnetic films with different thicknesses. After that, a spectroscopic ellipsometry is used to determine the optical parameter and the thickness of every layer of these samples, then the magneto-optical coupling constant of the multilayer magnetic ultrathin film can be obtained. After measurements of a series of ultrathin Fe films, the results show that the magneto-optical coupling constant Q is independent of the thickness of the magnetic film. The magneto-optical Kerr rotations and ellipticity are measured to confirm the validity of this experiment. Combined with the optical constants and the Q constant, the Kerr rotations and ellipticity are calculated in theory. The results show that the theoretical curve fits very well with the experimental data.     

Magnetism of a cobalt-gold planar nanostructure on the silicon surface

The structural and magnetic properties of a cobalt nanolayer placed between a silicon substrate and a protective gold layer are studied. At a cobalt layer mass thickness of 1–2 nm, a nanoisland structure is shown to form. This thickness range is characterized by a local maximum of the magnetooptical Kerr effect and enhanced nonlinear optical and magnetic nonlinear optical responses at the second-harmonic frequency. This enhancement can be caused by the excitation of local surface plasmons and an increase in the local fields at the probing-radiation and second-harmonic frequencies in metallic nanoislands. The surface-sensitive nonlinear magnetooptical Kerr effect at the second-harmonic frequency is maximal at a cobalt layer thickness of about 2 nm, which corresponds to the characteristic scale of magnetization formation in the near-surface layer in cobalt.     

The extended magneto optic method to explore the Longitude Magneto Optic Kerr effect of the ultrathin magnetic film grown on optic uniaxial substrate

A general method to solve the Magneto optic effect of the multilayer ultrathin films grown on the optic uniaxial crystal substrate has been developed by using a new boundary matrix. Based on this method, we can apply the magneto optic to any magnetic ultrathin film grown on uniaxial substrate as long as we choose a proper coordinate system. The formula for longitude Magneto Optical Kerr effect is derived to find out the influence of the optic properties of the uniaxial crystal on the magneto optic characteristics of multilayer system. A numerical simulation was carried out to find out the relation between Kerr rotation and optic properties of substrate. The result can be used to select the best suitable substrate on which the sample grown.     

Magnetic-Field-Induced Optical Second-Harmonic Generation Study of Co/Pt and Co/Ta Interfaces

Magnetic properties of an interface between cobalt and platinum or tantalum nanolayers have been studied by the optical second-harmonic generation and nonlinear magneto-optical Kerr effect methods. It has been shown that a high sensitivity of the second-harmonic generation method makes it possible to determine the orientation of the easy magnetization axis in the plane of a polycrystalline structure without measurement of the magnetic field dependence of second-harmonic generation. The comparison of the field dependences of magnetic-field-induced second-harmonic generation with the linear magneto-optical effect indicates the difference in the processes of magnetization reversal in Co/Pt and Co/Ta interfaces and the bulk of the cobalt film. In particular, a new linear in magnetization effect has been observed in the second harmonic that is symmetry-forbidden for uniformly magnetized structures.     

Exploring magnetic properties of ultrathin epitaxial magnetic structures using magneto-optical techniques

We describe magneto-optic Kerr effect studies of ultrathin Fe and Ni films on single crystal surfaces of Ag and Cu. Monolayer Fe films on Ag(100) exhibit the theoretically predicted spin-orbit anisotropy, but also yield some interesting discrepancies between behavior predicted by Kerr effect and by spin-polarized photoemission experiments. Layer-dependent studies of the magnetic moment of Ni on Ag(111) and Ag(100) suggest sp-d hybridization effects quench the first layer magnetic moment on Ag(111) but not on Ag(100). Temperature dependent studies of thin film magnetization obtained from Kerr effect measurements yield thickness dependent Curie temperatures, and critical exponents for several thin film systems.     

Magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in silicon oxide

The magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in the amorphous silicon oxide matrix are investigated as a function of the implantation dose. The analysis of the field dependences of the magnetization and the magneto-optical Faraday and Kerr effects demonstrates that, as the ion implantation dose increases, the superparamagnetic behavior of an ensemble of cobalt nanoparticles at room temperature gives way to a ferromagnetic response with the anisotropy characteristic of a thin magnetic film. The magnetization curves for the superparamagnetic and ferromagnetic ensembles of cobalt nanoparticles are simulated to determine their average sizes and the filling density in the irradiated layer of the silicon dioxide matrix. It is revealed that the spectral dependences of the Faraday and Kerr effects for ion-synthesized cobalt nanoparticles differ substantially from those for continuous cobalt films due to the localized excitations of free electrons in the nanoparticles.     

Co/GaAs(100)界面形成以及Co超薄膜磁性质的研究

利用同步辐射光电发射和铁磁共振(FMR)研究了Co/GaAs(100)界面形成以及Co超薄膜的磁性质.结果表明,在低覆盖度(约为0.2nm)下,Co吸附原子与衬底发生强烈的界面反应,在覆盖度为0.9nm时,形成稳定的界面.从衬底扩散出的Ga原子与Co覆盖层合金化,而部分As原子与Co原子发生反应,形成稳定的键合,这些反应产物都停留在界面处很窄的区域(0.3—0.4nm)内.另一部分As原子偏析在Co覆盖层表面.结合理论模型,详细地讨论了界面结构及Ga，As原子的深度分布.FMR结果表明,生长的Co超薄膜具 关键词：     

Runaway "fingerlike" instability of magnetic walls in ultrathin layers

We show that smooth domain walls in ultrathin ferromagnetic films can develop jaggedness even in the absence of random defects when confronted with a sufficiently large tilt between the uniaxial anisotropy direction and the external field. From the Kerr imaging of 0.7 nm thin Co films and from numerical simulations we report a previously unseen runaway fingerlike instability in a magnetic wall that begins on nanoscales but grows to macroscopic lengths for sufficiently large tilt angles. A threshold for the instability is controlled by the ferromagnet's parameters and the applied field.     

Structure and the magnetic and magneto-optical properties of Co-Sm-O nanogranular films

The magnetic properties and magneto-optical effects in nanocomposites based on Co-Sm-O films prepared through pulsed plasma sputtering of a SmCo₅ target are investigated. It is shown that, depending on the technological conditions and regimes of subsequent annealing, the films can have different structures from cobalt nanoparticles distributed in the dielectric samarium oxide matrix with a magnetic phase volume of more than 60% to a continuous polycrystalline cobalt film with embedded samarium oxide nanoparticles. The evolution of the spectra of the magneto-optical Kerr effect and the field dependences of the magnetization is studied as a function of the film structure.     

Versatile UHV system for combined far- and near-field magneto-optical microscopy of thin films

We have developed a UHV system for in situ studies of magnetic domains and magnetization reversal of thin films in the presence of external magnetic fields and at variable temperature. The system comprises a setup for magneto-optical Kerr effect measurements of magnetization curves, a Kerr-microscope for far-field magnetic-domain imaging, and a magneto-optical scanning near-field microscope in combination with a Sagnac interferometer (Sagnac-SNOM) for high-resolution imaging on a sub-μm scale. All components have successfully been tested, and the feasibility of studying ultrathin films has been demonstrated.     

Magnetic shape anisotropy calculations of Fe nanostructures at the Si/Fe(1 1 1) interface

The influence of Si capping layers on the magnetic properties of thin Fe films grown on Si(1 1 1) has been studied by means of shape anisotropy calculations. Fe surface morphology simulations are realized using experimental STM data. Surface modifications induced by the interaction between the Si overlayer and the Fe surface are performed in agreement with the model proposed in a previous work by Stephan et al. [J. Magn. Mater. 293 (2005) 746]. Calculations of the uniaxial anisotropy energy constant K_u are then performed on the modified Fe surface morphology for different Si deposition geometries as proposed in the model. The relevant data deduced by this method such as anisotropy constants and their related easy axis direction, are directly compared to the experimental ones obtained by ex situ magneto-optical Kerr effect (MOKE) measurements at room temperature using the transverse bias initial inverse susceptibility and torque (TBIIST) method. We show that a very good agreement between those results leads to a confirmation of the proposed model.     

Scaling properties of magnetic domain walls in Pt/Co/Pt trilayers on MgO (1 1 1)

We present a scaling analysis of the time evolution of domain walls in ultrathin magnetic films that are subject to different forms of uncorrelated and correlated disorder caused by the microstructure of the underlying template. The study is performed on ultrafine modulated Pt/Co/Pt trilayers grown on as-supplied and structured MgO (1 1 1) substrates employing polar Kerr microscopy for the imaging of the magnetic domains.