Magneto Optic Kerr Effect

An array of small independent and quasimonodisperse nanodots of the dilute magnetic semiconductor ͑Ga,Mn͒As with out-of-plane easy axis has been patterned by electronic lithography and ion-beam etching from a strained epitaxial film. The thermal dependence ͑2 Ͻ T Ͻ 120 K͒ of the field-induced magnetic loops, coercivity, and anisotropy of the nanodots, have been measured by sensitive magneto-optical magnetometry. Below the superparamagnetic blocking temperature T B , all results are consistent with a quasicoherent thermally activated and field-induced spin-rotation process. In spite of the nonconventional nature of the ferromagnetism mediated by holes and of the high dilution in manganese ions, T B is well accounted for by the usual Néel-Brown model.

PbSe is an unusual semiconductor material with a direct band gap at the L point of 150 meV at 4 K. The band structure at this symmetry point is four-fold degenerate for both electrons and light holes, and conduction and valence bands possess similar effective masses and g-factors. Since both masses are relatively small, quantum confinement effects are easily achieved by reducing the nanostructure size to dimensions of the order of the large exciton Bohr radius, a B =46 nm. We synthesized high quality PbSe nanocrystals and characterized them using transmission electron microscopy and optical methods. We probed the g-factor and fine structure of excitons in undoped PbSe quantum dots using optically detected magnetic resonance (ODMR) at 24 GHz and polarized photoluminescence in a magnetic field. The ODMR reveals that the g-factor is large for electron and holes (g=7.6) compared to other semiconductor nanocrystal systems. The photoluminescence polarization increases linearly with increasing magnetic fields up to 6 T, indicating that the fine-structure splitting is rather small.

Fine and hyperfine splittings arising from electron, hole, and nuclear spin interactions in the magnetooptical spectra of individual localized excitons are studied. We explain the magnetic field dependence of the energy splitting through competition between Zeeman, exchange, and hyperfine interactions. An unexpectedly small hyperfine contribution to the splitting close to zero applied field is described well by the interplay between fluctuations of the hyperfine field experienced by the nuclear spin and nuclear dipole/dipole interactions.

A three-dimensional ultrasound (3D-US) system suitable for laparoscopic surgery that uses a novel magneto-optic hybrid tracker configuration. Our aim is to integrate 3D-US into a laparoscopic AR system. A 5D miniature magnetic tracker is combined with a 6D optical tracker outside the body to perform 6D tracking of a flexible US probe tip in the abdominal cavity. 6D tracking parameters at the tip are obtained by combining the 5D parameters at the tip inside the body, the 6D parameters at the US probe handle outside the body, and the restriction of the tip motion relative to the handle. The system was evaluated in comparison with a conventional 3D ultrasound system. Although the accuracy of the proposed system was somewhat inferior to that of the conventional one, both the accuracy and sweet spot area were found to be acceptable for clinical use.

The magneto-optical (MO) Kerr effects for ZnO and ZnO:Ni-doped nanolaminate structures prepared using atomic layer deposition (ALD) have been investigated. The chemical composition and corresponding structural and morphological properties were studied using XRD and XPS and compared for both nanostructures. The 2D array gradient maps of microscale variations of the Kerr angle polarization rotation were acquired by means of MO Kerr microscopy. The obtained data revealed complex behavior and broad statistical dispersion and showed distinct qualitative and quantitative differences between the undoped ZnO and ZnO:Ni-doped nanolaminates. The detected magneto-optical response is extensively inhomogeneous in ZnO:Ni films, and a giant Kerr polarization rotation angle reaching up to ~2° was established. This marks the prospects for further development of magneto-optical effects in ALD ZnO modified by transition metal oxide nanostructures.

In a recent paper , it has been shown from transport measurements that artificial reversible pinning can be created by the application of a magnetic tape on the surface of a thin superconducting film. We study the influence of a periodic array of magnetic stripes, generated from a signal pre-recorded on a magnetic tape, on the pinning of vortices. With our high resolution magneto-optical technique [2], we visualize in two dimensions the penetration of the flux in a thin YBa2Cu307.~ film partially covered by such a magnetic tape. In particular, we investigate the evolution of flux entry in the superconducting strip under and next to the magnetic tape. We present results obtained for various temperatures and various applied fields.

We report the magneto-optical observation of a surprising fourfold symmetry of the flux penetration in a superconducting YBa 2 Cu 3 O 7Ϫ␦ thin-film disk containing a square array of antidots, leading to an angular variation of the critical current by a factor of nearly 2. This behavior is explained using a vortex channeling model. Potential applications in superconducting devices are discussed

Artificial pinning sites have been fabricated for the magnetic domain pinning in perpendicular anisotropy magneto-optical (MO) thin film media. The pinning sites were radial hole array made by patterning a layer of radial gold grid on the silicon nitride (SiN) coated silicon (Si) substrate using a standard electron beam lithography. Various magnetization and demagnetization procedures were performed to investigate the magnetic domain pinning behavior. A polar Kerr microscope was used in situ to monitor the magnetic wall motion and a magnetic force microscope was employed to scan the magnetic domain structures. Magnetic domains were found to be pinned inside the hole array and resembled to the geometric shape of the holes. The coercivity in the patterned MO layer is much higher than in the unpatterned MO layer. Moreover, the coercivity in the larger pinning sites area is higher than in the smaller pinning sites area.

A novel method for pinning the magnetic domain in artificially pinning hole has been developed for magneto-optical (MO) thin film material Dy,(FeCo)l.,. The artificially pinning holes were fabricated using electron-beam lithography. Hole arrays with square, star, and circle shapes had been made in this study. However, the nanometer scale magnetic domains could be formed inside the hole arrays if the pinning hole geometry was not well defined, and the pinning domain may induce media noise. Magneto-optical, nanometer domain, patterned substrate, pinned domain

We have studied growth and properties of quaternary alloy magnetic semiconductor (InGaMn)As grown both on GaAs substrates and on InP substrates by low-temperature molecular-beam epitaxy (LT -MBE). (InGaMn)As thin films were ferromagnetic below ~30 K, exhibiting strong magneto-optical effect. The lattice constant of [(In y Ga 1-y ) 1-x Mn x ]As, whose Mn concentration x is below 4%, is slightly smaller than that of In y Ga 1-y As with the same In/Ga content ratio. We have also obtained very smooth surface morphology of nearly lattice matched (InGaMn)As thin films grown on InP substrates, which is important for application to thin-film type magneto-optical devices integrated with III-V opto-electronics.

We developed a 1.5-mm-band, transverse-magnetic-mode waveguide isolator based on the nonreciprocal-loss phenomenon. The device consists of an optical waveguide with an InGaAs/InGaAlAs multiple-quantum-well amplifier and a ferromagnetic MnAs layer attached to the waveguide. The combination of the optical waveguide and the magnetized MnAs layer produces a magneto-optic effect called the nonreciprocal loss-a phenomenon where the propagation loss of light is larger in backward than in forward propagation. We present the guiding principle of the design of the structure of the device. A prototype device with a MBE-grown epitaxial MnAs layer showed a nonreciprocity of 9.8 dB/mm at a wavelength of 1.54 mm. Our device can be monolithically integrated with waveguide-based optical devices on an InP substrate.

We developed a 1.5-m band TM-mode waveguide optical isolator that makes use of the nonreciprocalloss phenomenon. The device was designed to operate in a single mode and consists of an InGaAlAs͞InP ridge-waveguide optical amplifier covered with a ferromagnetic MnAs layer. The combination of the optical waveguide and the magnetized ferromagnetic metal layer produces a magneto-optic effect called the nonreciprocal-loss phenomenon-a phenomenon in which the propagation loss of light is larger in backward propagation than it is in forward propagation. We propose the guiding design principle for the structure of the device and determine the optimized structure with the aid of electromagnetic simulation using the finite-difference method. On the basis of the results, we fabricated a prototype device and evaluated its operation. The device showed an isolation ratio of 7.2 dB͞mm at a wavelength from 1.53 to 1.55 m. Our waveguide isolator can be monolithically integrated with other waveguide-based optical devices on an InP substrate.

ABSTRACTWe present a time-resolved magneto-optical (MO) imaging study of high-temperature superconductor (HTS) in high-frequency alternating current (AC) regime. The evolution of the magnetic flux density distribution in YBa2Cu3O7-d (YBCO) thin film samples is studied in small steps of the phase of the applied AC current. The flux distribution at 10 K exhibits instabilities including flux jumps and flux creep. A quantitative analysis of the data allows us to obtain the current density evolution. The current profile changes considerably with the phase differently from the prediction of the critical state model. These observations can be explained by the higher self-field at the sample edge and the effects of flux creep.

The linear and quadratic Zeeman effects have been studied for two different neutral- acceptorbound-exciton complexes, (Ag, X) and (Cu, X), in high-purity p-type CdTe. For both complexes, the results are consistent with a bound-exciton ground state J= -in Tq symmetry. The relevant electron g value is g, = -1.77+0.02 for the electron, and E=+0.61+0.04 and I. = -0.04+0.02 for the hole parameters describing the isotropic and anisotropic Zeeman effects, respectively. The diamagnetic shift observed for the neutral- acceptorbound-exciton complex is well explained in terms of the pseudodonor model.

The magnetization profile of iron oxide magnetic nanoparticles (MNPs) and the binding ability of MNPs with metal ions in aqueous solutions were investigated by means of the magnetic linear dichroism (MLD) and the magneto-optical Kerr effect (MOKE) measurements. The ultra-visible MLD spectra of the non-modified and surface modified MNPs with -COOH showed a typical magnetization curve for a superparamagnetic particles. Also, the MLD spectra were changed drastically by the addition of dysprosium(III) ion and showed that MLD spectra can be used for the evaluation of metal-MNPs binding ability. Furthermore, the magnetization of MNPs solution was measured sensitively by the transversal MOKE measurements, where a polarized beam was reflected at the interface of prism/solution of MNPs.

Fel13TaS2 is a ferromagnetic intercalation compound. Band structure calculations show various deviations from the rigid band model. We suggest that the measured Kerr spectrum is due to four transitions with paramagnetic line shape from states situated near the Fermi level to higher lying Ta-states.

It is shown by model calculations that the dispersion of the diagonal part of the dielectric constant near the plasma edge in a metallic crystal has a strong influence on the magneto-optical properties. The plasma edge leads to resonancelike peaks in the Kerr rotation and Kerr ellipticity spectra and to a strong enhancement of the magnitude of the Kerr effect. The sharp and very large peaks observed in the Kerr effect of several transition-metal and rare-earth compounds are not necessarily related to sharp magneto-optical transitions, but could be a result of the presence of the plasma edge at the same fre- quency.

The magneto-optic interaction of waveguide light (WL) with spin waves (SW) in nonuniformly magnetized yttrium iron garnet (YIG) films was investigated both experimentally and theoretically. The measurements were carried out on YIG film of thickness 3.8 m at the optical wavelength of 1.15 m and in the SW frequency band of 3-4 GHz. It is shown that for collinear WL-SW interaction, a spatial nonuniformity of the magnetizing field can provide SW beam focusing and improve WL-SW interaction efficiency by a factor of an order of magnitude. Field nonuniformity in the transverse direction results in a spatial separation of regions of WL interaction with SW of different frequencies. For orthogonal geometry of the WL-SW interaction the artificial field nonuniformity leads to an increase in the Bragg diffraction angles.

The infrared magnetorefractive effect (MRE) is used to compare the magnetoresistance (MR) in epitaxial thin films of Fe3O4 grown on MgO with (100) and (111) crystal orientations. The smaller MRE detected in the (111) film is shown to correlate with the smaller electrically measured MR, its behavior consistent with a lower density of antiphase boundaries in the (111) film

The presence of enhanced magnetic fields in active regions is known to suppress acoustic power and modify oscillation frequencies. Applying the ring diagram technique to data from three different spectral lines at different heights in the solar atmosphere, we analyze the variation of the acoustic power with height. The data sets include simultaneous Dopplergrams obtained with the Ni I 676.8 nm from Global Oscillation Network Group (GONG), K I 769.9 nm from Magneto-Optical Filters at Two Heights (MOTH) and Na I 589.0 nm from MOTH and Mount Wilson Observatory (MWO). It should be noted that the Ni and K lines are formed in the photosphere while Na line is formed in lower chromosphere. Preliminary results suggest a difference in power suppression with increasing height, which can be explained in terms of the expanding magnetic flux tubes.

Effect of magnetic field on interaction of non-polarized light with a one-dimensional magneto-optic resonator has been investigated. Attention has been given to resonators with isotropic zero-field magneto-optic medium inside them. It has been shown that, in the presence of multi-beam interference, the Faraday effect is also observed in non-polarized light. Faraday rotation is manifested in significant changes of transmission and reflection spectral characteristics of the resonator in magnetic field. It has been ascertained that magnetic field substantially changes the interferential pattern for transmission and reflection of non-polarized light. The results of investigations show the possibility to use the magneto-optical resonators and resonator structures for controlling external nonpolarized light passing through them.

A 1.5-m nonreciprocal-loss waveguide optical isolator having improved transverse-magnetic-mode (TM-mode) isolation ratio was developed. The device consisted of an InGaAlAs/InP semiconductor optical amplifier waveguide covered with a ferromagnetic epitaxial MnSb layer. Because of the high Curie temperature (T c ¼ 314 C) and strong magneto-optical effect of MnSb, the nonreciprocal propagation of 11-12 dB/mm has been obtained at least up to 70 C.

MgB2 is one of the most unstable superconducting materials, where flux jumps are commonly observed at low temperatures jeopardizing its potential for applications. We present a detailed MO imaging study of the jumps in MgB2 films, where we observe large dendritic flux patterns as well as much smaller jumps down to 50 flux quanta. The large jumps destroy the critical

The photo-induced modifications of the strong magneto-optic Kerr effect have been studied in a semimagnetic semiconductor microcavity operated in the strong coupling regime. These are traced to the saturation and many body interaction blue shift of the exciton transition frequency, which result in a photo-induced reduction of the effective exciton -cavity coupling. Its impact is most striking in the case of initially tuned microcavity, where a modification of the exciton-cavity coupling results in photo-induced polarization rotations of about 30 degrees for laser fluences as low as 1 mJ/cm 2 and magnetic field intensities of 0.2 T.

We present magneto-optical reflectivity results in the basal plane of the hexagonal MgB 2 . The data were collected on a mosaic of MgB 2 single crystals with T c 38 K from the ultraviolet down to the far infrared as a function of temperature and magnetic field oriented along the c axis. In the far infrared, there is a clear signature of the superconducting gap with a gap ratio 2=k B T c 1:2, well below the weakcoupling value. The gap is suppressed in an external magnetic field, which is a function of temperature. We extract the upper critical field H c2 along the c axis. The temperature dependence of H c2 is compatible with the Helfand-Werthamer behavior.

Yttrium iron garnet (YIG) film made as a magneto-optical medium suffers from the problem of crack formation, caused by the heating process. YIG thin film is deposited by radio frequency RF magnetron sputtering; the obtained layer is amorphous and it needs annealing to be crystallized. After heat-treatment at 740 o C of the sample realized on quartz substrate, we observe cracks on the entire film surface. This is due to the large difference between the thermal expansion coefficient (5.5 x 10 -7 K -1 for quartz and 10 x 10 - 6 K -1 for YIG). In this paper we present a new fabrication method to reduce this problem, we make a multilayer to obtain at the end a uniformly unique layer with excellent crystalline structure. Such films have the possibility to reach a thickness of 500 nm. YIG films have been studied by Rutherford Backscattering Spectrometry (RBS), optic Ellipsometry and the Scan Electron Microscope. The RBS spectra were collected in channelling geometry with incident particles energy 2 MeV and 3.5 MeV. The thickness and the stoichiometric value of the thin films have been evaluated. Simulation of all spectra indicates a constant composition. Ellipsometry method is well adapted to model the thin film structure layers, and to measure the thickness of the film and the complex index of refraction. The theoretical ellipsometric value of the index of refraction is (2.22) while the experimental value is ranging from 2.2 to 2.3 for a wavelength of 1550nm.

We present a magneto-optical system to study semiconductor heterostructures in the presence of an external biaxial tensile strain. The pressure cell is based on the deflection of a plate (the sample) placed between a sphere and a ring. This externally applied stress is easily controlled and can achieve a deformation of up to ∼0.25% for GaAs films. This device is very useful for band structure study and optical resonance experiments in heterostructures. We also present the application of the device to study the behavior of the magneto-excitons in InP epitaxial layer as a function of the biaxial strain. We observed that the diamagnetic and Zeeman effects in InP films are affected by the biaxial tensile strain.

In this paper we investigate the effect of a static magnetic field and of an optical pumping on the transmittance of a hybrid graphene-split ring resonator metasurface. Experimental evidence of a significant modulation of the transmitted spectra has been observed, both for what concerns the sole optical pumping, and for the combination of optical pumping and magnetostatic bias. The transmittance modulation traces retain peculiar spectral fingerprints which induces the interpretation of the phenomenon as a non-trivial interplay between the bare graphene response and the split ring resonance.

The magneto-optical effect of lyotropic liquid crystal at isotropic phase doped with different concentrations of ferrofluid (FF) is investigated. The samples are placed between crossed polarizers and submitted to a pulsed magnetic field. The experimental results are interpreted by means of Bernoulli's approach and a characteristic time is discussed.

In this paper we investigate the effect of a static magnetic field and of an optical pumping on the transmittance of a hybrid graphene-split ring resonator metasurface. Experimental evidence of a significant modulation of the transmitted spectra has been observed, both for what concerns the sole optical pumping, and for the combination of optical pumping and magnetostatic bias. The transmittance modulation traces retain peculiar spectral fingerprints which induces the interpretation of the phenomenon as a non-trivial interplay between the bare graphene response and the split ring resonance.

The asymmetric magnetization reversal in exchange biased Fe/MnF 2 involves coherent (Stoner-Wohlfarth) magnetization rotation into an intermediate, stable state perpendicular to the applied field. We provide here experimentally tested analytical conditions for the unambiguous observation of both longitudinal and transverse magnetization components using the magneto-optical Kerr effect. This provides a fast and powerful probe of coherent magnetization reversal as well as its chirality. Surprisingly, the sign and asymmetry of the transverse magnetization component of Fe/MnF 2 change with the angle between cooling and measurement fields.

Spin waves offer intriguing novel perspectives for computing and signal processing, since their damping can be lower than the Ohmic losses in conventional CMOS circuits. For controlling the spatial extent and propagation of spin waves on the actual chip, magnetic domain walls show considerable potential as magnonic waveguides. However, low-loss guidance of spin waves with nanoscale wavelengths, in particular around angled tracks, remains to be shown. Here we experimentally demonstrate that such advanced control of propagating spin waves can be obtained using natural features of magnetic order in an interlayer exchange-coupled, anisotropic ferromagnetic bilayer. Using Scanning Transmission X-Ray Microscopy, we image generation of spin waves and their propagation across distances exceeding multiple times the wavelength, in extended planar geometries as well as along one-dimensional domain walls, which can be straight and curved. The observed range of wavelengths is between 1 µm and 150 nm, at corresponding excitation frequencies from 250 MHz to 3 GHz. Our results show routes towards practical implementation of magnonic waveguides employing domain walls in future spin wave logic and computational circuits.

We present a computational method for the ab initio study of magneto-optical quantities like the optical conductivity and the magneto-optical Kerr rotation based on density-functional theory. This method is tested here on the ferromagnetic metals Fe and Ni. The results for Fe agree very well with experimental data. The magneto-optical polar Kerr rotation is predicted accurately. For Ni the results are in fair agreement with experiment. In those points where deviations from experimental data are found, they can be traced back to the well-known fact that the local-density approximation is of moderate success in describing some of the Ni 3d bands.

The vibrational distribution P͑y͒ of Na 2 1 ions created in ultracold collisions in a magneto-optical trap has been determined. Only two vibrational states with y 2 and 3 are populated and we find P͑2͒ 0.29 6 0.02 and P͑3͒ 0.71 6 0.02. The results provide conclusive evidence that the ionization mechanism is photoassociative autoionization, and not photoassociative photoionization, and will form a fundamental test for the theoretical description of the process. [S0031-9007(97)

We constructed a magneto-optical microspectroscopy apparatus in the infrared region using a synchrotron radiation, SPring-8. In the apparatus, an infrared microscope with the spatial resolution of B11 mm is combined with low temperatures ðX3:5 KÞ and high magnetic fields ðp14 TÞ: The purpose is to investigate the electronic structure under extreme conditions of tiny materials such as organic conductors and of small region and the spatial distribution of electronic structures. After the installation of high pressure cells, optical measurements under multiple-extreme conditions is available. The specification of the apparatus and recent results of an organic superconductor are presented.

We have observed the spatial inhomogeneity of the electronic structure of a single-crystalline electron-doped EuO thin film with ferromagnetic ordering by employing infrared magneto-optical imaging with synchrotron radiation. The uniform paramagnetic electronic structure changes to a uniform ferromagnetic structure via an inhomogeneous state with decreasing temperature and increasing magnetic field slightly above the ordering temperature. One possibility of the origin of the inhomogeneity is the appearance of magnetic polaron states.

Pyrochlore Tl 2 Mn 2 O 7 has been found to exhibit a colossal magneto-resistance (CMR) that is comparable to that for the perovskite manganites such as La 1Àx Sr x MnO 3 : In order to probe the microscopic electronic structures of Tl 2 Mn 2 O 7 ; we have measured its optical conductivity sðoÞ in wide ranges of photon energy, temperature (T), and external magnetic field (B). We have observed very strong variations of sðoÞ with T and B near the Curie temperature, where the CMR manifests itself. Analyses on the variations in sðoÞ show that both T-and B-induced evolutions of the electronic structures in Tl 2 Mn 2 O 7 are very similar to each other, and that they are universally related to the development of macroscopic magnetization. We have also observed a pronounced Kerr rotation at the plasma edge of the reflectivity.

We constructed a magneto-optical microspectroscopy apparatus in the infrared region using a synchrotron radiation, SPring-8. In the apparatus, an infrared microscope with the spatial resolution of B11 mm is combined with low temperatures ðX3:5 KÞ and high magnetic fields ðp14 TÞ: The purpose is to investigate the electronic structure under extreme conditions of tiny materials such as organic conductors and of small region and the spatial distribution of electronic structures. After the installation of high pressure cells, optical measurements under multiple-extreme conditions is available. The specification of the apparatus and recent results of an organic superconductor are presented.

PACS 78.47.jc -Time resolved spectroscopy PACS 78.20.Ls -Magnetooptical effects PACS 75.70.Ak -Magnetic properties of monolayers and thin films Abstract. -The time resolved Magnetooptical Kerr effect in the substrate-strain-induced insulating ferromagnetic phase in (Pr0.6Ca0.4)MnO3 thin films on two different substrates was measured in a magnetic field up to 1.1T. The photoinduced Kerr rotation and ellipticity show remarkably different magnetic-field dependence. From the comparison of the magnetic field dependencies of the photoinduced and static Kerr rotation and ellipticity we conclude that a transient ferromagnetic metallic phase, embedded within the insulating ferromagnetic phase, is created upon the photoexcitation at low temperatures. A comparison of temporal dependence of the photoinduced Kerr signals with the photoinduced reflectivity indicates the change of the fractions of the phases takes place on a timescale of ten picoseconds independent of the substrate.

Vortex avalanches are known to occur in MgB 2 films within a certain range of temperatures and magnetic fields. These events, resulting from a thermomagnetic instability, were first revealed by real-time magneto-optical imaging, which exposed dendritic paths of abrupt flux propagation. This very powerful technique has, however, a practical limitation, since sensors that are currently available cannot be used at high magnetic fields. This letter shows that results obtained using dc magnetometry are in good correspondence with those furnished by magneto-optical imaging, demonstrating that the two techniques can be efficiently used as complementary tools to map vortex avalanches in superconducting films.

We have employed magneto-optical imaging to visualize the occurrence of flux avalanches in a superconducting film of a-MoGe. The specimen was decorated with square antidots arranged in a square lattice. We observed avalanches with the anomalous habit of forming trees where the trunk is perpendicular to the main axis of the square lattice, whereas the branches form angles of 45 degrees. The overall features of the avalanches, and in particular the 45 degree direction of the branches, were confirmed by numerical simulations.

We have constructed a three-configurational surface magneto-optical Kerr effect system, which provides the simultaneous measurements of the “polar,” “longitudinal,” and “transverse” Kerr hysteresis loops at the position where deposition is carried out in an ultrahigh vacuum growth chamber. The present system enables in situ three-dimensional vectorial studies of ultrathin film magnetism with a submonolayer sensitivity. We present three-configurational hysteresis loops measured during the growth of Co films on Pd(111), glass, and Pd/glass substrates.

Two, lightweight diode laser frequency stabilization systems designed for experiments in the field are described. A significant reduction in size and weight in both models supports the further miniaturization of measurement devices in the field. Similar to a previous design, magnetic field lines are contained within a magnetic shield enclosing permanent magnets and a Rb cell, so that these dichroic atomic vapor laser lock (DAVLL) systems may be used for magnetically sensitive instruments. The mini-DAVLL system (49 mm long) uses a vapor cell (20 mm long) and does not require cell heaters. An even smaller micro-DAVLL system (9 mm long) uses a microfabricated cell (3 mm square) and requires heaters. These new systems show no degradation in performance with regard to previous designs while considerably reducing dimensions.

The possibility of the use of the nonlinear Faraday effect for optical limitation of the laser power is investigated in a resonant Faraday medium placed between two crossed polarizers. The results are comparable with those obtained at strong magnetic fields as a result of the linear Faraday effect. Advantages of the method are the narrow bandwidth and the wide field of view. The investigations are interesting from the viewpoint of applications for optical sensor protection and automation of the experiment. All measurements are performed at the F g ϭ 2 3 F e ϭ 1 hyperfine structure transition of the 87 Rb D1 line.

The magnetization reversal processes in Fe 20 Ni 80 dot arrays have been studied both experimentally and theoretically. The circular-shaped dots with thickness of 60 nm and variable diameters of 0.2-0.8 m were fabricated by using electron-beam lithography and lift-off technique. A size dependent vortex nucleation, annihilation and initial susceptibility were determined from magneto-optical hysteresis loops. With increasing dot diameter the nucleation and annihilation fields decrease, whereas the initial susceptibility exhibits a linear increase. The experimental data were compared to the results of analytical calculations taking into account magnetostatic interactions, exchange and Zeeman energies for a planar array of magnetically soft circular dots.

A magnetometric technique is demonstrated that may be suitable for precision measurements of fields ranging from the sub-microgauss level to above the Earth field. It is based on resonant nonlinear magneto-optical rotation caused by atoms contained in a vapor cell with anti-relaxation wall coating. Linearly polarized, frequency-modulated laser light is used for optical pumping and probing. If the time-dependent optical rotation is measured at the first harmonic of the modulation frequency, ultra-narrow (∼ a few Hz) resonances are observed at near-zero magnetic fields, and at fields where the Larmor frequency coincides with half the light modulation frequency. Upon optimization, the sensitivity of the technique is expected to exceed 10 -11 G/ √ Hz.