The Faraday effect in the rhombohedral weak ferromagnet FeBO 3 , which is due to the magnetization component parallel to the С 3 axis of the crystal, is predicted and experimentally observed for the first time. This magnetization component is almost three and a half orders of magnitude smaller than the magnetization in the basal plane. The measured effect is six orders of magnitude smaller than the Faraday effect caused by the magnetization in the basal plane. The origin of the significant difference in the magnitudes of the Faraday effect due to the magnetization in the basal plane and to the magnetization parallel to the С 3 axis is discussed.

The Faraday effect in the rhombohedral weak ferromagnet FeBO3, which is due to the magnetization component parallel to the С3 axis of the crystal, is predicted and experimentally observed for the first time. This magnetization component is almost three and a half orders of magnitude smaller than the magnetization in the basal plane. The measured effect is six orders of magnitude smaller than the Faraday effect caused by the magnetization in the basal plane. The origin of the significant difference in the magnitudes of the Faraday effect due to the magnetization in the basal plane and to the magnetization parallel to the С3 axis is discussed.

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.

With the use of magneto-optical Faraday effect effective field of perpendicular magnetic anisotropy of iron garnet films is measured in vacuum and in the atmosphere of water vapor. It is established that a decrease of the mentioned field takes place due to adsorption of the water molecules by 20% in comparison with the value of field in vacuum. This result is in accordance with the conclusion reached on the base of investigation of influence of water molecules adsorption on domain structure of iron garnet films earlier.

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.

Due to water molecules adsorption the reversible change of domains width and domain structure reconstruction in bismuth-doped ferrite-garnet thin films with perpendicular magnetic anisotropy was observed. The change of domains width was 15% in saturated water vapor at room temperature. The decrease of domains width is explained by the reduction of effective perpendicular magnetic anisotropy constant due to water molecules adsorption.

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.

A theory of the surface magnetism of iron borate, FeBO3, allowing for the non-ideality of the crystal structure of the near-surface layer is constructed. Since the magnetizing field of a near-surface layer appears to be inversely proportional to the tenth power of the crystal lattice parameter, the influence of the non-ideality on the surface magnetism should be substantial. The suggested models of reconstruction make it possible to describe experiments if the magnitude of the deformations is in agreement with literature data. The theoretical dependence of the value of the surface anisotropy on the concentration of point defects in a near-surface layer of the crystal is also established.

Influence of water molecules reversible adsorption on domain structure and domain wall structure in amorphous Fe-rich ferromagnet samples is investigated by magnetooptical method. Before investigation the samples were kept in the air. Domain structure of the samples significantly changes in wacuum: instead one 180-degree domain wall several domain walls appear which are oriented with angle 45o to the long side of the sample. This effect is completely reversible. Another new effect is found: domain wall width on the sample surface in vacuum is 35% bigger (13.5 µm) than in atmosphere of water vapor (10 µm).

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.

It was founded using the magneto-optical technique that the domain wall in the iron-based amorphous ferromagnet in its movement experienced enhanced deceleration on the surface compared to the volume. The surface deceleration of the wall intensifies under water molecules adsorption on the sample surface. This effect is explained by the domain wall interaction with magnetic micro-defects observed on the sample surface using a magnetic force microscope.

It is established that reversible adsorption of water and methyl alcohol molecules, occurring via formation of hydrogen bonds, changes the dynamic properties of domain walls in the surface region of soft ferromagnets, as well as their initial static magnetic susceptibility. A mechanism is proposed for the effects revealed.

Magnetic structure of inhomogeneously magnetized near-surface magnetic layer for non-basal faces of FeBO3 single crystals has been calculated. That layer has macroscopic thickness and can be observed in easy-plane weak ferromagnets. The calculation is based on our theory of Iron Borate surface magnetism.