V.E. Zubov

Influence of adsorption-desorption processes on dynamics of 180° domain wall in iron

Abstract Motion of a single 180-degree domain wall in perfect monocrystals of iron was investigated in a vacuum cell by a magnetooptic method with micron-resolution. It was found, that the relaxation frequency of the domain wall increased by more than one order with the decrease of the air pressure from 10 5 to 10 3 Pa.

Near-surface magnetic structures in iron borate

Abstract Surface magnetism on natural non-basal faces of iron borate monocrystals was found and analysed by means of the magneto-optical and Bitter methods. The surface magnetism here is represented by a macroscopical transition magnetic layer, the result of surface magnetic anisotropy. Anisotropy is caused by the change in surface magnetic ion environment symmetry. The erasure of surface magnetism at a face of the (10 1 4)-type takes place in a field of H c = 1.6 kOe, the same characteristic for faces of the (11 1 0) and (11 2 3)-types is ⪅ 100 Oe. By measuring the temperature-critical field relationship in the temperature range from 77 K upto the Neel point, it was found that H c is proportional to the crystals magnetization. Surface anisotropy energy and the structure of transition magnetic layers are calculated for the analyzed types of faces. The developed theory gives a correct description of surface magnetic anisotropys symmetry, yields the H c field value order which agrees with the experimentally determined one, and also explains the temperature-critical field relationship.

A new method of measuring hysteresis loops on local areas of the surface of a ferromagnet

Abstract We describe a new method of measuring hysteresis loops from local areas of the surface of a ferromagnet, based on the employment in a magneto-optical micromagnetometer of new linear magneto-optical effects in reflected light: the meridional and polar intensity magneto-optical effects. High-sensitivity measurements of magnetization curves are achieved using the modulation of the plane of light polarization.

Anomalous influence of physical adsorption on the magnetic properties of iron single crystals

Abstract An essential distinction between the surface and volume dynamic properties of 180° domain walls in iron whiskers that is not explained by the existent theory is determined. With the help of magneto-optical investigations in a vacuum cell, it is established that the reason for the abnormal behaviour of domain walls is the physical adsorption of molecules contained in the air on the whisker surface.

Effect of reversible adsorption on the magnetic properties of iron garnet films

The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.

Reversible-adsorption-induced variation of domain width in iron garnet films

It has been found using the Faraday-effect magneto-optic method that the width of magnetic domains of the labyrinth domain structure in bismuth-containing iron garnet films with perpendicular anisotropy changes considerably after the adsorption of methanol molecules. A maximum change in domain width of 50% has been observed in methanol saturated vapor. This effect is reversible. A decrease in domain width under adsorption has been attributed to a decrease in the effective constant of the perpendicular magnetic anisotropy of the film caused by the adsorption of methanol molecules.

Perpendicular surface magnetic anisotropy in an amorphous ferromagnet induced by adsorption occurring through the mechanism of the formation of hydrogen bonds

It has been found that the domain structures of amorphous magnetically soft iron-based ferromagnetic ribbons in an atmosphere of water vapor and methyl alcohol are significantly different. In the former case, several domains separated by domain walls oriented at an angle of 30°–40° to the long side of the sample are observed. In the latter case, two domains separated by one wall located in the middle of the sample in parallel to its long side are observed. In the former case, the normal component of the magnetization on the sample surface has been detected using the polar magnetooptical Kerr effect. In the latter case, the normal component of the magnetization is almost absent. The observed effects are reversible. The normal component of the magnetization is induced by the desorption of water and methyl alcohol molecules, which are absorbed through the mechanism of the formation of hydrogen bonds, from the sample surface. According to the performed estimate, the effective field of the perpendicular magnetic anisotropy reaches a value of 1.6 kA/m.

Anomalous surface deceleration of a domain wall in an amorphous ferromagnet

On soft magnetic amorphous specimens, a rapid decrease in the surface amplitude of 180° domain wall oscillations relative to the bulk amplitude is observed with increasing frequency of the magnetizing field. The dynamics of the domain wall is studied by a magnetooptical method at the specimen surface and by the induction method in the bulk. The results of the experiment disagree with the theory, which takes into account the effect of eddy currents and predicts that, with increasing frequency, the surface amplitude of the domain wall oscillations should decrease slower than the bulk amplitude. The observed behavior of the domain wall is explained by its interaction with macroscopic defects at the specimen surface. This interaction gives rise to unsteady chaotic surface wall displacements, which lead to an increase by several orders of magnitude in the effective surface damping parameter in the Landau-Lifshits equation.

Influence of Physisorbed Water Molecules on the Dynamics of Domain Wall in an Amorphous Ferromagnet

It was found that physisorbed water molecules affect the near-surface dynamics of a 180° domain wall in an amorphous FeCuNbSiB ferromagnet. In the range of water vapor pressures 400–1300 Pa, the oscillating domain walls suffer enhanced damping in the near-surface region and reduce their relaxation frequency from 10 to 4 kHz. This effect is explained by the influence of surface magnetic defects arising due to the pressure produced by the clusters of physisorbed water molecules on the walls of micropores at the magnet surface.

Effect of reversible adsorption of water molecules on the magnetic susceptibility of iron borate

A change in the quasistatic magnetic susceptibility in thin plates of iron borate (FeBO3), which is a weak ferromagnet, has been revealed at adsorption of water molecules. The measurements have been performed at room temperature with the use of the magneto-optical Faraday effect. The change of the susceptibility in saturated water vapors is about 30%. The observed effect is reversible. The time of establishing the susceptibility after the introduction of water vapors is 1.5 min, which is twice as large as the time of establishing the susceptibility after the evacuation. The effect is explained by the appearance of uniaxial surface magnetic anisotropy in the basal plane because of the adsorption of water molecules.