Local Magnetic Vector Research Articles

Investigation of Co-rich amorphous microwires by help of magneto-optical method with micron resolution

Results on the magneto-optical investigation of near-surface micromagnetic structure of Co 69Fe 4Si 12B 15 amorphous wires 10–50 μm in diameter are presented. By scanning the light spot of 1-μm-diameter along the wire length, distributions of magnetization components and also local hysteresis characteristics of the wires were measured. It was experimentally established that the examined microwires have a circumferential magnetic anisotropy. In consequence, there are the near-surface alternate left- and right-handled circular domains in these samples. The dependencies of the circular domain width on the wire diameter and length were found. It was proved that the dominant mechanism of the wire magnetization reversal in the axial magnetic field is rotation of local magnetization vectors in circular domains.

57 Fe Mössbauer spectroscopy applied to the study of rare-earth iron permanent magnets

A survey of some important applications of 57Fe Mossbauer spectroscopy to the study of local magnetic and structural characteristics of the main phases in the rare-earth-transition metal (RE–TM) class of materials used in the development of the new generations of high performance permanent magnets is presented. A brief history of the hard magnets evolution in the last decades is followed by the description and interpretation of the main effects on the hyperfine interactions revealed by the Mossbauer technique. The contribution of the distinct crystallographic iron sites to the saturation magnetization of the rare-earth iron compounds is discussed in terms of the corresponding types of magnetic coupling, based mainly on the iron–iron distances, the number of iron neighbors and the respective hyperfine fields. These features are inferred from the energy of the resonant absorption by the iron sites 4e/4c/8j1/8j2/16k1/16k2 in the Nd2Fe14B, sites 6c/9d/18f/18h in the light RE2Fe17N3 and 8f/8i/8j in the RE(Fe12-xTMx) phases. The direction of the easy axis of magnetization is discussed taking into account the effects due to the interaction between the local magnetization vector and the electric field gradients. Some other characteristics such as the occupancy of the TM atoms in the 1 : 12 compounds as well as in some hybrid (Fe +TM) 2 : 17 structures are also discussed in terms of the changes in the relative subspectral areas. The effects regarding charge transfers and lattice expansions due to the incorporation of nitrogen and also of other different interstitial elements to the 2 : 17 rhombohedral structure are discussed considering the relative changes of the isomer shifts in comparison with the alterations in the parameter due exclusively to the respective volume expansions.

Magneto-optical investigation of micromagnetic structure of Fe-rich amorphous ribbons and wires

The results on the magneto-optical investigation of the magnetization processes and near-surface micromagnetic structure (MMS) of Fe-rich soft magnetic amorphous ribbons and wires are presented. The strong dispersion (in macro- and microscale) of magnetic anisotropy in the studied samples was discovered. In consequence of it, their local magnetic properties were very inhomogeneous. It was proved that magnetization processes of the samples realize by means of incoherent rotation of local magnetization vectors. The buckling and curling modes of the magnetization reversal were observed in ribbons and wires correspondingly. It was established that at a some value of magnetic field the blocking of magnetization processes exists. It was discovered that thermomagnetic annealing of the studied ribbons strongly influence on their local magnetic properties and MMS.

On the differentiation between the magnetic anomalies of cylinders and disks

The magnetic anomaly patterns due to thin lateral deposits of ore can be very similar to those due to deposits in extended magma root structures which potentially may be more important from a geophysical point of view. New forms of the solutions for the anomalous magnetic field due to vertical cylinders and to thin disks are given; these are suitable for fast computation. For various values of the local magnetization vector of the body, the measured anomaly patterns are obtained and features are identified which serve to differentiate the patterns due to a thin disk from those due to a semi-infinite vertical cylinder.

Incoherent rotations in thin films with in-plane anisotropy

The hard axis magnetization process in thin ferromagnetic films has been investigated by Lorentz electron microscopy. At the onset of an external magnetic field the local magnetization vectors of the individual domains rotate incoherently. To describe these rotations an internal field is introduced. The magnitude of this field and its evolution during the magnetization process are calculated in terms of experimentally measured directions of local magnetization. The internal field increases as the domains appear, attaining two extreme values and then gradually vanishes close to saturation. Its maximum value depends on the width of stripe domains arising when the film is magnetized along the hard axis. The internal field is the main factor determining the shape of the hysteresis loop.

Ferromagnetic resonance line dispersion in polycrystalline ferrites

Results of a theoretical and experimental investigation of the influence of pores and nonmagnetic inclusions on the ferromagnetic resonance line dispersion in polycrystalline ferrites are elucidated in this paper. The absorption line dispersion is computed with the deflection of the local magnetization vector from the magnetizing field direction taken into account, where the dispersion is described by linear terms in the generation and annihilation operators in the Hamiltonian of the interacting spin wave system. The theory and experiment are compared in a broad range of variation of the porosity in different ferrites. The field of anisotropy of the ferrites investigated is calculated from the second moment of the absorption line.

On the stability of certain magnetic modes in fine ferromagnetic particles

Conditions of stability of the magnetization curling mode in fine spherical and cylindrical particles and of the magnetization helicoid structure in fine cylindrical particles are derived, and magnetization reversal processes in such particles are considered. The application of Ritz's method for solving the variational problem of finding the local magnetization vectors in the volume of a particle provides a convenient way of finding the conditions mentioned above. It has been shown that the magnetization curling mode in a spherical fine particle with radius larger than a critical one is stable in a well-determined interval of the external magnetic field, provided the magnetocrystalline anisotropy constant is less than a certain value K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . In such a case the hysteresis loop of a spherical particle measured in an easy direction is no longer rectangular. The magnetization curling and helicoid modes are both unstable in fine cylindrical particles with positive or zero values of the magnetocrystalline anisotropy constant. The hysteresis loop of such particles magnetized along the axis of rotation is rectangular.

"Lorentz" microscopy of stripe domain films with protons

A new method is reported for observing the in-plane component of magnetic structure in stripe domain films. Stripe domain films act as a Faraday-effect diffraction grating, and deflect light beams in a way reminiscent of electrons being deflected by the Lorentz force in a magnetic thin film. The direction of the stripes is that of the local in-plane magnetization vector. Thus the angle of deflection is perpendicular to the local in-plane magnetization, as is the case for Lorentz deflection. Micrographs are presented demonstrating that with a displaced aperture one can perform with light the analogues of the two modes of Lorentz microscopy: light-field microscopy in the defocused mode and dark-field microscopy with light normal to the film plane. In the defocused mode, walls appear as either bright streaks or dark streaks; if one focuses on the opposite side of the film the bright walls become dark and vice-versa. In the dark-field mode the contrast of the dark regions and the bright regions can be reversed by moving the aperture.

On the Effective Field Retarding the Process of Incoherent Rotation

AbstractThe internal effective field He retarding the process of incoherent rotation during the switching of thin magnetic films was investigated. The principal results of the work are as follows. If the switching field Hs exceeds the incoherent threshold field, He increases rapidly with time t (from the value ≈︁ Hk), reaches (t ≦ 10 ns) the maximum value H close to (0.9 to 0.95)Hs, then falls off monotonically, tending in the limit to a value close to ‐Hk. The main contribution to the value of He is made by the effective anisotropy field and the stray fields formed as a result of the initial rotation of the local magnetization vectors.

Magnetic Vector Study of Regional and Local Geologic Structure in Principal Oil States

The local magnetic vectors at the United States Coast and Geodetic Survey stations in Louisiana, Texas, Arkansas, Oklahoma, Kansas, Mississippi, Alabama, and California have been computed by deducting the normal values of the earth's magnetic field from the absolute measurements, at each station, of the declination and of the vertical and horizontal magnetic intensities. The local magnetic vectors have been plotted as vector triangles at the respective stations on the vector maps of the different states. These vectors indicate the intensity and the direction in space of the magnetic lines of force, as due to local magnetic anomalies mainly within the first 15,000 feet of subsurface. As local magnetic anomalies are, with negligible exceptions, the result of geologic features, either of structural or petrographic character, a large amount of regional and local geologic information is obtained by a study of these maps. The main magnetic anomalies of the different states have been interpreted in terms of geology, though no attempt has been made to exhaustively interpret all vectors. The vector maps show at a glance which areas are of interest for magnetometer surveys, what size anomalies may be expected, how far a magnetometer survey has to be extended, or where it is best commenced to cover a certain area. As the vectors are of sufficient accuracy, they allow a checking and tying-in of scattered magnetometer surveys.