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Domain wall mobility as a function of nonmagnetic interlayer thickness and temperature was studied in ultrathin exchange-coupled ferromagnetic layers using magneto-optic Kerr microscopy. The system under study is a Pt/Co/Pt/Co/Pt heterostructure having perpendicular magnetic anisotropy and a middle Pt layer with spatially variable thickness. The ferromagnetic interaction between the Co layers is observed when the Pt interlayer thickness varies from 5 to 6 nm in a temperature range of 200–300 K. There is a certain interval of Pt layer thickness where domain walls in both ferromagnetic layers move independently. Nonlinear dependence of the domain wall displacement on the applied field was measured. It is shown that an equilibrium position of the relaxed domain wall depends on field, temperature, and the nonmagnetic interlayer thickness. This position is determined by the energy balance: (i) domain wall displacement provided by the applied field, (ii) interlayer exchange interaction in the area swept by the domain wall, and (iii) domain wall coercivity. The mechanism of domain wall stabilization in terms of independent wall motion near critical thickness was considered. It is found that both the coercivity of the Co layer and the critical thickness decrease at higher temperature, while the interlayer exchange constant J is changed weakly. [ABSTRACT FROM AUTHOR]

A field theory is proposed to extend the standard piezoelectric framework for linear elastic solids by accounting for the presence and motion of dislocation fields and assessing their impact on the piezoelectric properties. The proposed theory describes the incompatible lattice distortion and residual piezoelectric polarization fields induced by dislocation ensembles, as well as the dynamic evolution of these fields through dislocation motion driven by coupled electro-mechanical loading. It is suggested that (i) dislocation mobility may be enhanced or inhibited by the electric field, depending on the polarity of the latter, (ii) plasticity mediated by dislocation motion allows capturing long-term time-dependent properties of piezoelectric polarization. Due to the continuity of the proposed electro-mechanical framework, the stress/strain and polarization fields are smooth even in the dislocation core regions. The theory is applied to gallium nitride layers for validation. The piezoelectric polarization fields associated with bulk screw/edge dislocations are retrieved and surface potential modulations are predicted. The results are extended to dislocation loops. [ABSTRACT FROM AUTHOR]

Domain structure and magnetization reversal process of exchange-coupled ferromagnet/antiferromagnet bilayers Co(x)/Ir¿Mn(10 nm) were studied as a function of both thickness of the Co layer and annealing temperature. The exchange bias field of the thinnest film and the coercive field of the thicker films show monotonic increase at annealing temperature above 250 °C. In every case the bilayers are remagnetized by domain nucleation and domain wall motion. Domain size decreases rapidly for high annealing temperatures, while x-ray diffraction study indicated that the crystallographic texture did not change significantly. The observed features are discussed taking into account the magnetic structure at the interface and its evolution during annealing. [ABSTRACT FROM AUTHOR]

The magnetization reversal processes in an epitaxial Fe/[Sm.sub.2][Co.sub.7] structure were investigated using the magneto-optical indicator film technique. The dependence of the magnitude and the orientation of the structure average magnetization have been studied on both cycling and rotating the external magnetic field. Magnetization reversal of the soft ferromagnet was found to proceed by the formation of exchange springs due to spin winding in both the thickness and perpendicular directions as adjacent subdomains with opposite chirality are created. Experimental data is compared with a theoretical estimation of the rotational hysteresis loop for a spin system containing a one-dimensional (single chirality) exchange spring. Index Terms--Exchange spring, magnetization reversal, permanent magnet, SmCo, thin film.

The hybrid exchange spring behavior in a bilayer consisting of an epitaxial film of Fe (500 A˚)/Sm[SUB2]Co[SUB7](350 A˚) deposited onto a Cr (200 A˚) buffered MgO(110) substrate was investigated using the magneto-optical indicator film technique. Two critical magnitudes of the remagnetizing magnetic field were found that dramatically change the bilayer remanent magnetization. One of them is determined by exchange spring penetration in the interface; another is determined by hybrid spin spiral transformation to domain walls in the hard ferromagnet layer. Unexpected dependence of the direction of average remanent magnetization on the external magnetic field direction and value is revealed. [ABSTRACT FROM AUTHOR]

Domain processes were observed at 300 K using the magneto-optic indicator film technique (MOIF) in an exchange-coupled ferromagnet (FM)/antiferromagnet (AF) bilayer Fe[SUB76]Mn[SUB6]C[SUB18] (150 Å)/FeMn (100 Å) deposited under the presence of a 0.4 mT magnetic field (H) applied in the plane of the sample. The hysteresis loop for this sample was comprised of two half-loops symmetrically shifted in opposite directions from the origin. At H = 0, MOIF observations showed the presence of domains in the FM with magnetization (M) vectors along the axis of the preparation field separated by 180° walls. Upon field application along that axis, saturation of the FM was achieved by the nucleation and growth of domains. In this state, at not very high fields, it was possible to observe an unusual MOIF contrast at the location of the original FM domain walls in the as-prepared ground state, associated with the intersection of domain walls in the AF with the FM. Upon field reduction M reversed only in regions which had reversed during the prior field application, so that at H = 0 the domain structure was the same as that in the original ground state. If H was off-axis, during the original field application domain growth occurred in that same direction; upon field reduction, the preferred domain growth direction was at an angle with reversed sign. These results prove the AF domain walls do not move during the motion of FM domain walls, and that an exchange spring is created parallel to the AF/FM interface as the ferromagnetic layer reverses. [ABSTRACT FROM AUTHOR]

The details of the magnetization reversal in coupled ferromagnetic Co/Ru/Co trilayers deposited on obliquely sputtered Ta underlayers were studied using the magneto-optical indicator film technique. The ground states of the sandwich are characterized by noncollinear magnetization orientations in the two Co layers, which can be remagnetized by the motion of 180° and non-180° domain walls. In the latter case, the angle between the magnetization vectors in the adjacent domains was revealed to be about ± 100°, and an anomalous magnetization reversal was observed. The canted magnetization states and their mutual transformations are discussed in terms of the competition between ferromagnetic coupling through pinholes and antiferromagnetic coupling across the Ru layer. [ABSTRACT FROM AUTHOR]

The magnetic domain structure, magnetic properties, and thermal stability of IrMn biased top spin valves containing Co and NiFe have been investigated. The magneto-optical indicator film pictures of Ni-Fe biased IrMn spin valve show the formation and motion of domain walls that separate large domains in the free film unlike the Co biased IrMn spin valve structure with many small microdomains. From the angular dependence of the ferromagnetic resonance linewidth (ΔH) and resonance field (H[sub res]) it was found that the IrMn biased Co film is very different from the behavior of a NiO biased Permalloy film which exhibits two-magnon scattering. To investigate the thermal stability two kinds of magnetoresistance measurements at anneal temperature (T [sub Anm]) and room temperature (T[sub RT]) following anneals were accomplished. [ABSTRACT FROM AUTHOR]

Macroscopic domain structures have been realized in wedged-permalloy (Py)/uniform-FeMn bilayers during magnetization reversal. When the exchange anisotropy is established perpendicular or parallel to the wedge direction, two macroscopic domains are observed. Separating these domains are a 180° wall in the perpendicular geometry and an intermediate band containing large density of stripe-type microdomains in the parallel geometry. While the exchange field remains practically the same in both geometries, the coercivity and squareness of the loop are much less in the parallel geometry. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study of the magnetization process of granular cobalt-silver films. Use of the magneto-optical indicator film technique and magnetic force microscopy in the study; Quality characterization of high-temperature superconductors; Analysis of magnetization domains.

We have studied FeMn/Ni81Fe19 bilayers using vectorial vibrating-sample magnetometry (VSM) and the magnetooptic-indicator-film (MOIF) technique and observed stationary antiferromagnetic (AF) domain walls throughout the hysteresis process. The FeMn/Ni81Fe19 bilayer was demagnetized at 450 K and then cooled to 300 K in a zero field. The resultant hysteresis loop at 300 K clearly shows two loops, one shifted to the left of the origin and the other, to the right. Moreover, one loop is slanted and the other is square, indicating that the two sets of ferromagnetic (FM) domains have noncollinear magnetizations. At the zero applied field, the MOIF images clearly reveal the FM domains and domain walls. These domain walls, however, are hybrid domain walls connecting both FM and AF domain walls. With the application of a magnetic field, the FM domain walls can be swept. But, regardless of the applied field, including the case where the FM layer has been made into a single domain, domain walls at the original locations are still visible. Of the two sets of the FM domains with different magnetic-anisotropy axes, one set becomes reversed by rotation during magnetization reversal, while the other set becomes reversed by domain-wall nucleations and propagations. [ABSTRACT FROM AUTHOR]

Presents a study which utilized the ferromagnetic layers in suitably structured bilayers to provide information on the underlying antiferromagnetic layer. Experiment; Memory effects of exchange bias; Conclusions.