A. Maziewski

Magneto-optical anisometry of ultrathin cobalt films

The advantage of magneto‐optics to measure magnetic anisotropy constants in ultrathin films exhibiting perpendicular spin anisotropy is reported. This is illustrated for Au/Co/Au sandwiches with Co layer thickness ranging from 8 to 15 A. We stress the importance of preliminary measurements always necessary to define the (H∥,H⊥) region in which a homogeneous spin rotation occurs. These results confirm the existence of interface anisotropy and lead to its estimation Ks=0.56 erg/cm2 whereas the volumic term is shown to be Kv=7.5×106 erg/cm3.

Magnetic and magnetoresistive properties of NiFe/Au/Co/Au multilayers with perpendicular anisotropy of Co layers

The giant magnetoresistance (GMR), magnetization reversal, and domain structure of magnetron sputtered spin valve [NiFe/Au/Co/Au]N multilayers consisting of ferromagnetic layers with alternating in-plane (NiFe) and out-of-plane (Co) magnetic anisotropy has been investigated. For 0.4 3, the neighboring magnetic layers were observed to be coupled. This coupling is of magnetostatic origin. The effective coupling field, estimated from GMR dependencies, is of the order of 100 kA/m. Micromagnetic simulations confirm that the domain structure of Co layers influences the behavior of NiFe layers.

Direct imaging of the magnetization reversal in microwires using all-MOKE microscopy

We report a method of imaging of the magnetization reversal process using analysis of real-time images of magnetic domain structures in cylindrically shaped microwires. This method uses wide-field polarizing optical microscopy and is based on the magneto-optical Kerr effect (MOKE). The aperture diaphragm in MOKE microscope was used to control the incident angles of the light rays that reached the non-planar surface of the microwire and also determined the MOKE geometries. The movement of the non-central position of the hole in this diaphragm leads to a change in the orientation of the plane of incidence of the light along the perpendicular or the parallel direction to the axial direction of the wire. The visualization of the surface magnetic domain structures is obtained using polar and longitudinal MOKE geometries. The hysteresis loops were obtained by plotting the averaged image contrast as a function of the external magnetic field. The separation of the all-magnetization components is performed using different MOKE geometries in a microscope. We demonstrate the use of vector magnetometry to analyze the orientation of the magnetization in a cylindrically shaped microwire under the influence of an external magnetic field.

Spin reorientation transitions in Pt/Co/Pt films under low dose Ga+ ion irradiation

An elegant route for tuning the magnetic anisotropy of ultrathin Co films by Ga+ ion irradiation is presented. The magnetic anisotropy of a Pt/Co(2.6 nm)/Pt film is first changed from in-plane to out-of-plane by uniform low dose Ga+ ion irradiation at 30 keV. When increasing the dose, a second spin reorientation transition toward the sample plane is also evidenced. This could be a way to design magnetic nanowires with perpendicular anisotropy, embedded in an in-plane magnetized environment, either by irradiation through a mask or focused ion beam. Tentative explanations on the origin of these two successive spin reorientations are proposed.

Magnetic field induced transition from weak to strong ferromagnetic coupling in NiFe∕Au∕Co∕Au multilayers

We report on a specific magnetostatic coupling in sputter deposited (Ni80Fe20∕Au∕Co∕Au)10 multilayers of alternating in-plane and out-of-plane magnetic anisotropies. We demonstrate on the basis of complementary studies (magnetoresistance, conventional magnetometry, and element specific soft x-ray resonant magnetic scattering hysteresis measurements) that the magnetization reversal of the Ni–Fe layers is strongly influenced by a magnetostatic coupling originating from the out-of-plane stripe domain stray fields of the Co layers.

Unexpected magnetization processes in YIG + Co films

Abstract Unidirectional properties (shifts of BH loop) were observed in (YCa)3(FeCoGe)5O12 films grown on (100) GGG substrate. These shifts could be flipped by an external field (≈ 50 Oe) applied along the normal to the film or in the sample plane. The properties are similar to those of magnetic materials characterized by unidirectional anisotropy (e.g. exchange-coupled soft and hard magnetic system). The proposed domain structure model of a homogeneous sample with mixed magnetic anisotropy explains these peculiarities reasonably well. The formula for the estimation of a self-biasing field vector is given for a multi-easy axes magnet. The magnetization processes were investigated using the Faraday effect (domain structure image was analyzed visually and digitally), low frequency magnetic susceptibility technique and a vibrating sample magnetometer. The room temperature FMR spectra and the Faraday rotation spectra were analyzed, too. Microscopic theory and domain structure model are discussed for the explanation of the previously reported effects: (i) unexpectedly low and changeable domain wall velocity v (v, which depends on the width of the applied field pulses, is in the approximate range 1 sm/s-220 m/s); (ii) domain structure shape memory.

Null ellipsometer with phase modulation

A new null ellipsometer is described that uses photoelastic modulator (PEM). The phase modulation adds a good signal-to-noise ratio, high sensitivity, and linearity near null positions to the traditional high-precision nulling system. The ellipsometric angles Delta and psi are obtained by azimuth measurement of the analyzer and the polarizer-PEM system, for which the first and second harmonics of modulator frequency cross the zeros. We show that the null system is insensitive to ellipsometer misadjustment and component imperfections and modulator calibration is not needed. In addition, a fast ellipsometer mode for fine changes measurement of ellipsometric angles is proposed.

Single antidot as a passive way to create caustic spin-wave beams in yttrium iron garnet films

Single antidot as a passive point excitation source has been implemented to create caustic spin-wave beams in yttrium iron garnet film. Diffraction of surface magnetostatic spin waves from such antidot is investigated experimentally and theoretically. Our experimental results from Brillouin light scattering spectroscopy indicate that the diffraction beams, which manifest as reflection, extinction, and semicaustic lines, are tunable by the frequency and direction of the incident wave. Numerical calculations are in good agreement with the experimental findings and explain the directions of caustic beams caused by the diffraction.

Direct observation of giant Barkhausen jumps in magnetic microwires

Magnetization reversal induced by a circular magnetic field has been studied using the magneto-optical Kerr effect in magnetic microwires. The visualization of the classical effect of a giant Barkhausen jump is reported in a magnetic microwire. It was directly confirmed that the surface giant Barkhausen jump consists of the nucleation of a single circular domain followed by the long distance quick motion of the solitary circular domain walls.

Drastic changes of the domain size in an ultrathin magnetic film

A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is p...