Year of publication
- Direct observation of two-dimensional self-focusing of spin waves in magnetic films (1999)
- The first observation of self-focusing of dipolar spin waves in garnet film media is reported. In particular, we show that the quasi-stationary diraction of a nite-aperture spin wave beam in a focusing medium leads to the concentration of the wave power in one focal point rather than along a certain line(channel). The obtained results demonstrate the wide applicability of nonlinear spin wave media to study nonlinear wave phenomena using an advanced combined microwave-Brillouin light scattering technique for a two-dimensional mapping ofthe spin wave amplitudes.
- Brillouin light scattering from quantized spin waves in micron-size magnetic wires (1999)
- An experimental study of spin wave quantization in arrays of micron size magnetic Ni80Fe20 wires by means of Brillouin light scattering spectroscopy is reported. Dipolar-dominated Damon-Eshbach spin wave modes laterally quantized in a single wire with quantized wavevector values determined by the width of the wire are studied. The frequency splitting between quantized modes, which decreases with increasing mode number, depends on the wire sizes and is up to 1.5 GHz. The transferred wavevector interval, where each mode is observed, is calculated using a light scattering theory for confined geometries. The frequen-cies of the modes are calculated, taking into account finite size effects. The results of the calculations are in a good agreement with the experimental data.
- Collisions of Spin Wave Envelope Solitons and Self-Focused Spin Wave Packets in Magnetic Films (1999)
- Head-on collisions between two-dimensional self-focused spin wave packets and between quasi-one-dimensional spin wave envelope solitons have been directly observed for the first time in yttrium-iron garnet (YIG) films by means of a space- and time-resolved Brillouin light scattering technique. We show that quasi-one-dimensional envelope solitons formed in narrow film strips ("waveguides") retain their shapes after collision, while the two-dimensional self-focused spin wave packets formed in wide YIG films are destroyed in collision.
- Biased Switching of small magnetic particles (1999)
- High frequency switching of single domain, uniaxial magnetic particles is discussed in terms of transition rates controlled by a small transverse bias field. It is shown that fast switching times can be achieved using bias fields an order of magnitude smaller than the effective anisotropy field. Analytical expressions for the switching time are derived in special cases and general configurations of practical interest are examined using numerical simulations.
- Enhanced coercivity of exchange-biased Fe/MnPd bilayers (1999)
- We present detailed studies of the enhanced coercivity of exchange-bias bilayer Fe/MnPd, both experimentally and theoretically. We have demonstrated that the existence of large higher-order anisotropies due to exchange coupling between different Fe and MnPd layers can account for the large increase of coercivity in Fe/MnPd system. The linear dependence of coercivity on inverse Fe thickness are well explained by a phenomenological model by introducing higher-order anisotropy terms into the total free energy of the system.
- Arrays of Interacting Magnetic Dots and Wires: Static and Dynamic Properties (1999)
- Static and dynamic properties of patterned magnetic permalloy films are investigated. In square lattices of circular shaped permalloy dots an anisotropic coupling mechanism has been found, which is identified as being due to intrinsically unsaturated parts of the dots caused by spatial variations of demagnetizing field. In arrays of magnetic wires a quantization of the surface spin wave mode in several dispersionless modes is observed and quantitatively described. For large wavevectors the frequency separation between the modes becomes smaller and the frequencies converge to the dispersion of the dipole-exchange surface mode of a continuous film.
- Ferromagnetism above room temperature in Mn-Si-C alloy films (1999)
- Mn-Si-C alloy films are prepared by e-beam coevaporation onto a Si substrate held at 600 °C. Ferromagnetism is observed below T = (360 +/- 5) K with SQUID magnetometry and magneto-optical Kerr effect. This is the highest Curie temperature T yet observed for a Mn-based alloy. Although the composition determined by Auger depth profiling varies appreciably for different films, their T is the same indicating that ferromagnetism is caused by an alloy of well-defined composition independent of precipitations.
- Switching behavior of a Stoner particle beyond the relaxation time limit (1999)
- We report results of the switching properties of Stoner-like magnetic particles subject to short magnetic field pulses, obtained by numerical investigations. We discuss the switching properties as a function of the external field pulse strength and direction, the pulse length and the pulse shape. For field pulses long compared to the ferromagnetic resonance precession time the switching behavior is governed by the magnetic damping term, whereas in the limit of short field pulses the switching properties are dominated by the details of the precession of the magnetic moment. In the latter case, by choosing the right field pulse parameters, the magnetic damping term is of minor importance and ultrafast switching can be achieved. Switching can be obtained in an enlarged angular range of the direction of the applied field compared to the case of long pulses.
- Anisotropic magnetic coupling of permalloy micron dots forming a square lattice (1997)
- Static magnetic and spin wave properties of square lattices of permalloy micron dots with thicknesses of 500 Å and 1000 Å and with varying dot separations have been investigated. A magnetic fourfold anisotropy was found for the lattice with dot diameters of 1 micrometer and a dot separation of 0.1 micrometer. The anisotropy is attributed to an anisotropic dipole-dipole interaction between magnetically unsaturated parts of the dots. The anisotropy strength (order of 100000 erg/cm^3 ) decreases with increasing in-plane applied magnetic field.
- Brillouin light scattering investigations of structured permalloy films (1999)
- The static and spin wave properties of regular square lattices of magnetic dots of 0.5-2 microm dot diameter and 1-4 microm periodicity patterned in permalloy films have been investigated by Brillouin light scattering. The samples have been structured using x-ray lithography and ion beam etching. The Brillouin light scattering spectra reveal both surface and bulk spin wave modes. The spin wave frequencies can be well described taking into account the demagnetization factor of each single dot. For the samples with smallest dot separation of 0.1 microm a fourfold in-plane magnetic anisotropy with the easy axis directed along the pattern diagonal is observed, indicating anisotropic coupling between the dots.