Complex Domain Patterns Research Articles

One- and two-dimensional magnetization processes in amorphous alloys

The hysteresis loop and loss properties of near-zero-magnetostrictive amorphous ribbons have been investigated as a function of the induced macroscopic magnetic anisotropy Ku from dc to 10 kHz. It is found that, following the evolution of Ku, imposed by means of sequential field annealings along the longitudinal (LD) and transverse (TD) directions, the hysteresis loop shape and area and the frequency dependence of energy losses suffer dramatic changes, dictated by the value of Ku and the local distributed anisotropies K. On passing from longitudinal to transverse macroscopic easy axis, coherent spin rotations come into play and, in association with the domain wall displacements, eventually provide a net magnetization reversal along both LD and TD. The hysteresis loss component Wh correspondingly increases and the energy loss at high frequencies decreases. It is concluded that: (1) optimal quasi-static magnetic behavior requires relatively high and positive Ku values (>50–100 J/m3), with longitudinal plane rigid walls and (2) the best high frequency properties are attained for Ku∼0, where flexible walls and complex domain patterns are created.

Surface magnetic microstructure of melt-spun magnetic ribbons

Scanning electron microscopy with polarization analysis (SEMPA) and photon-excited spin polarized secondary electron spectroscopy have been used to study respectively the lateral variations and depth profiles of the surface magnetic microstructure of as-cast amorphous melt-spun Fe80B20 ribbons. The 5 μm resolution SEMPA images showed very similar complex domain patterns for both remanent and field-on states, and spot mode hysteresis loops showed significant differences across the sample. These data are consistent with a very wide distribution of strain-induced anisotropy fields. Energy resolved hysteresis loops (ERHL) measured using photoemitted 1 and 20 eV secondary electrons showed clear differences in form, attributable to changes in probing depth. A unidirectional anisotropy found in the 20 eV ERHL is linked tentatively to the inhomogeneities revealed by SEMPA.

Perpendicular magnetic anisotropy, domains, and misfit strain in epitaxial Ni/Cu1-xNix/Cu/Si (001) thin films.

We have investigated the magnetic anisotropy in epitaxial Ni/${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$/Cu/Si (001) thin films (0x50%) as a function of Ni thickness h and alloy substrate composition. Also the average in-plane biaxial strain ${\mathit{e}}_{0}$(h) in Ni/Cu (001) (x=0) was measured ex situ versus Ni thickness using optical interferometry. We observed that the preferred direction of magnetization is perpendicular to the films over an exceptionally broad Ni thickness range for films kept under UHV: 10 \AA{}h60 \AA{} in Ni/Cu (001); 20 \AA{}h40 \AA{} in Ni/${\mathrm{Cu}}_{60}$${\mathrm{Ni}}_{40}$/Cu (001). We have also studied the perpendicular magnetic anisotropy by magnetic force microscopy and observed a complex domain pattern characterized by two length scales and very strong contrast. We have analyzed our results using a phenomenological model that includes the bulk magnetoelastic anisotropy energy (${\mathit{B}}^{\mathit{b}}$${\mathit{e}}_{0}$) and both the surface magnetocrystalline (${\mathit{K}}^{\mathit{s}}$/h) and the surface magnetoelastic (${\mathit{B}}^{\mathit{s}}$${\mathit{e}}_{0}$/h) anisotropy energies. Our analysis yields the magnetic surface energies ${\mathit{K}}^{\mathit{s}}$ and ${\mathit{B}}^{\mathit{s}}$ of the vacuum/Ni (001) and Ni/Cu (001) interfaces. The origin of the strong perpendicular magnetic anisotropy lies in the surface energy ${\mathit{K}}^{\mathit{s}}$ corresponding to the Ni/Cu (001) interface and the bulk magnetoelastic anisotropy energy. The surface magnetoelastic anisotropy energy ${\mathit{B}}^{\mathit{s}}$${\mathit{e}}_{0}$ favors an in-plane magnetization. The effective magnetoelastic coupling coefficient depends strongly on h for h\ensuremath{\le}150 \AA{} and changes sign near h\ensuremath{\approxeq}28 \AA{}. The two observed in-plane to out-of-plane magnetization easy-axis transition thicknesses are predicted by our pheomenological model. The lower magnetization easy-axis transition is not due to the onset of misfit dislocations at the Ni/Cu interface.

Complex ferroelastic domain patterns in Pb2CoWO6(=PCW) observed with the polarized-light microscope

Polarized-light microscopy of Pb2CoWO6in transmitted light reveals complex domain patterns in the transition range from the monoclinic/incommensurate phase to the orthorhombic one. As long as both phases coexist, a domain state with unique compensation properties appears.

High field, high frequency magnetic dynamics of narrow thin-film magnetic multilayer stripes

The dynamic surface magnetic response and flux propagation in arrays of multilayer magnetic thin-film stripes subject to high frequency magnetic fields has been studied using scanning Kerr imaging and a high frequency permeameter respectively. Scanning Kerr Images of the regions of surface response to a uniform oscillating magnetic field of up to 2 Oc between 1 and 50 MHz identify the domain state and surface permeability of the multilayer films. Transitions among the expected easy-axis laminated, hard axis, closure domain and a new complex domain state are observed as the total and magnetic layer thicknesses, stripe widths and field history are changed. As expected, the high frequency magnetic response of single layer films is dominated by magnetization rotation at low field, while closure domain wall motion becomes significant above the coercivity. Easy-axis domain state multilayer films, in narrow structures those films with magnetic layers a few hundredÅngströms thick or less, exhibit a uniform high permeability over the entire surface of the film. The dynamics of the new complex domain pattern seen in narrow multilayer films with thicker magnetic layers is complicated, with a blotchy, hysteretic magnetic response from the center of the strip and a immobile, mostly hard-axis oriented region along the edge.

High resolution electron microscopic study of the hexagonal bronze potassium niobium tungstate (PNT)

High-resolution electron microscopic studies are reported on the nature of the complex domain patterns which occur in the room temperature phase of the hexagonal bronze KWNb2O9. Two-dimensional lattice images reveal the domain wall configurations, with walls having virtually zero thickness, containing steps (kinks) of atomic dimensions. Wall rearrangements, following kink propagation under the influence of the electron beam, are also described. Symmetrical zone axis images, for extremely thin edges of the specimens, reveal directly the nature of the (W, Nb) atom displacements responsible for the hexagonal component of the superstructures occurring throughout five phases, which exhibit a series of structural phase transitions, including ferroelectric phases, in the temperature range 270-560°C.

Charged wall behavior in 1-µm bubble implanted structures

The domain wall pattern around a non-implanted disk and its coupling with an underlying 1-μm bubble are revealed by using colloid technique with Ferrofluid. The complex domain patterns are interpreted graphically from a three-vertex critical curve, similar to the process in uniaxial permalloy films by using the Stoner-Wohlfarth's four-vertex critical curve. The critical curve is also used to explain the charged wall's whip and flip motions during magnetization reversal around the disk.

Domains in Thin Magnetic Films Observed by Electron Microscopy

A new method for observing full domains in thin magnetic films by electron microscopy is described. Observations are made with standard transmission instruments utilizing an off-centered objective aperture diaphragm as a knife edge. The method has the high-resolution advantage that the microscope is focused on the specimen during domain observations. Limitations of the method and comparisons with the previously reported defocusing technique are presented. Applications to the interpretation of complex domain patterns and cross-tie walls are demonstrated. The observations were made with electrostatic-focusing microscopes, the AEG-Zeiss and Trüb-Täuber instruments, which allow the use of full objective power without influencing the magnetization distribution of low coercive force films. A second method using a knife edge is proposed that would potentially permit a simple measurement of the detailed magnetization distribution of a domain wall in a thin film.