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The stray field magnitude and distribution, at sensor level, have been investigated as a function of the thickness of the shield, the presence of a domain wall in the shield, the relative position of the vortex accompanying the wall and its proximity to the Air-Bearing-Surface (ABS). Using micromagnetics, the stray fields at the reader sensor have been simulated while a domain wall moves in a shield near the ABS in a magnetic head. For shield thicknesses from 640 nm to 1280 nm, a range of interest for head design, the domain wall shape is C-shaped with a vortex-like structure on either side of the domain wall that provides flux closure inside the film. For a 5 Oe incidental field, the wall exits at the ABS in less than 20 ns when the wall is between the ABS and the vortex. Average stray fields reached 60 Oe while 100 Oe localized stray fields are observed as the wall exits the ABS. The dynamics of wall motion change when the vortex is between the ABS and the domain wall. A 5 Oe incidental field in a 640 nm thick shield drove the wall toward the ABS, compressing the vortex and creating a blocking structure. An incidental 10 Oe field twisted the wall center magnetization enough to change wall chirality accelerating the wall exit, preventing the blocking structure, and flipping the vortex to the other side of the wall. Average stray fields are 55 Oe with a local maximum of 70 Oe. Similar results occur for a 1280 nm thick shield for a 50e field, with average stray fields of 60 Oe and a local maximum of 100 Oe. Index Terms--Blocking structure, chirality, domain wall, noise, stray field.

Magnitudes and distributions of stray magnetic fields from a single domain wall in a Permalloy film are calculated for film thickness from 10 nm to 2.5 [micro]m, using direct integration of the Landau--Lifshitz--Gilbert equation in a Cartesian lattice. This thickness range supports a Neel wall whose magnetization rotates in the plane of the film, a symmetric Bloch wall whose magnetization rotates out of the plane, and an asymmetric Bloch wall whose magnetization rotates simultaneously in and out of the plane of the film at the surfaces and inside the film, respectively. The stray field magnitude is largest for films with a Neel wall rather than film with a Bloch wall. The stray field magnitude varies linearly with thickness for films with Neel walls. The field distribution has a Neel-dominant character, i.e., it lies in a plane perpendicular to the plane of the wall, parallel to the plane of the film, and is dominated by the tranverse component of the field. For films with a Bloch-type component, the stray field is lower. The field distribution has a Bloch-dominant character, i.e., it lies in a plane perpendicular to the plane of the wall, normal to the plane of film, and is dominated by the normal component of the field. At thickness larger than 1 [micro]m, the stray field appears independent of thickness and is relatively constant at 15 Oe. Index Terms--Bloch domain wall, Neel caps, permalloy, stray field.

Cross-tie walls in permalloy films have been simulated as a function of thickness in the range 10-70 nm using direct integration of the Landau-Lifshitz-Gilbert equation in a Cartesian lattice with periodic boundary conditions along the length of the wall. A cross-tie wall is a Bloch-like transition along the wall for vertical Bloch line (VBL)] between Neel Walls of opposite chirality in a film with in-plane magnetization. This transition is a low-energy state, which allows the long tails of Neel walls to partially close their magnetic flux in the vicinity of the walls. The magnetization configuration of these transitions is either elliptical (vortex) or hyperbolic (antivortex). The pi-VBL transitions are 50 nm in diameter and the distance from each other increases with film thickness. The cross-tie wall energy per unit area was lower than that of a pure Neel or Bloch wall between 15 and 50 nm film thickness. Index Terms--Cross-tie wall, Neel caps, Neel wall, permalloy, symmetric and asymmetric Bloch wall, VBL, wall energy.

In this work we have studied the behavior of the bamboo domains under stress ([Sigma]), tension (+ [Sigma]) as well as compression (-[Sigma]), with the aim of making the domain model of the negatively magnetostrictive (-[[Lambda].sub.s]) CoSiB wire clear. It is observed that the growth of the surface bamboo domains due to [Sigma] has directivity depending on the orientation of the underlying core domain. In one orientation the black bamboo domain grows, while in the opposite orientation the white domain grows. From the stress behavior of the bamboo domains we have concluded that the domain model of -[[Lambda].sub.s], wire consists of two spiral domains of opposite rotation and proposed a new model. Index Terms - bamboo domains, domain model, spiral domains of opposite rotation, stress

The dynamics of a single three dimensional 2[Pi]vertical Bloch line (2[Pi]VBL) structure in a domain wall in garnet have been investigated using large scale numerical simulations. The domain wall distorts when a 2[Pi]-VBL is present at equilibrium. For a film thickness of 1.28 [[micro]meter], a maximum wall tilt of 400 [Angstrom] (2 [degrees]) was found at the 2[Pi]VBL. The 2[Pi]VBL longitudinal wall microdeformation is 1.22[[micro]meter], or almost twice the 2[Pi]VBL width. When fields normal to the film surface are applied, wall and 2[Pi]VBL velocities, along with VBL to wall velocity ratio, are calculated. At fields lower than 10 Oe, the velocity ratio at dynamic equilibrium is equal to 7.5. It is half the theoretical ratio [Pi][square root of Q]/2[Alpha] (Quality factor Q=4.0, damping constant [Alpha]=0.2) for a periodic chain of [Pi]VBLs. At fields between 10 to 12 Oe, saturation velocities of 10 m/s and 80 m/s are calculated for the wall and 2[Pi]VBL respectively. At higher fields, horizontal Bloch lines (HBLs) are nucleated on each side of the 2[Pi]VBL structure. Both the wall and 2[Pi]VBL velocities decrease along with the velocity ratio.

The dependence of the magnetic properties of amorphous wire on the diameter have been investigated. The anisotropy constant, hence the internal stress, of the wire increases with the wire diameter. The size of the pinned reverse domain at the wire end increases with the wire diameter. Domain observation shows that irrespective of the change in the wire diameter, the domain structure basically consists of chevron domain layer sandwiched between the surface maze domain and the inner core domain.

Co-Fe-Si-B films have been prepared using a roll coater and DC magnetron sputtering system onto a polyethylene terephthalate substrate. This thin film exhibited an excellent uniaxial anisotropy introduced by an asymmetric thermal shrinkage of the substrate. Reversal with a single large Barkhausen pulse has been observed in a thin film structure 1mm by 50mm by 0.65 [[micro]meter]. Closure domains have been clearly identified at the film ends. The threshold for the reversal is the coercive force. The reason for reversal with a single Barkhausen jump is that the long narrow film geometry has essentially zero demagnetizing field over most of the film. Once the walls start to move through the center portion of the film, there is nothing to stop them so the reversal proceeds with a single large Barkhausen pulse.

Domain observations were made on Fe and Co based amorphous magnetic wires that exhibit a large Barkhausen discontinuity during flux reversal. Domain patterns observed on the wire surface were compared with those found on a polished section through the center of the wire. It was confirmed that the Fe based wire consists of a shell and core region as previously proposed, however, there is a third region between them. This fairly thick transition region made up of domains at an angle of about 45 degrees to the wire axis clearly lacking the closure domains of the previous model. The Co based wire does not have a clear core and shell domain structure. The center of the wire had a classic domain structure expected of uniaxial anisotropy with the easy axis normal to the wire axis. When a model for the residual stress quenched-in during cooling of large Fe bars is applied to the wire, the expected anisotropy is consistent with the domain patterns in the Fe based wire, however, shape anisotropy still plays a dominant role in defining the wire core in the Co based wire.

The dynamic structure of a magnetic domain wall in a stripe compression experiment has been investigated by numerical integration of the Landau-Lifshitz-Gilbert equation. We consider domain walls of the type found in thin film materials with a large uniaxial anisotropy perpendicular to the plane of the material. We find that a single Horizontal Bloch Line (HBL) is formed in the domain wall and is responsible for wall overshoot and saturation of the wall velocity. These results compare favorably with experimental data.

The dynamics of a magnetic domain wall containing vertical Bloch line winding pairs (2Pi VBL) has been numerically investigated. The wall is of the kind found in thin film materials with a large anisotropy perpendicular to the plane of the film. The 2Pi VBLs are all of the same chirality and are periodically repeated along the wall at equal spacing. The wall is driven by an applied field perpendicular to the film plane and the VBLs move gyrotropically. Starting from an equilibrium shape, the 2Pi VBLs distort. If the field is low enough, a new dynamic shape is established that is quite stable. Above a threshold, the distortion pulls the 2Pi VBLs apart into a Pi VBL chain before the dynamic equilibrium structure is established. This breakup is accompanied by a discontinuous jump in both wall and VBL mobility.

The mechanism of re-entrant flux reversal in Fe-Si-B amorphous wires was investigated by domain observation and reverse domain detection focusing on the magnetic properties near the wire ends. It was found that the wire consists of shell and core domains and that the core region has the residual reversing domain due to demagnetizing field near wire ends in a remanent state. The residual domain was stabilized by forming a flux closure structure through the shell domain, which increases the threshold field for domain growth to a value much larger than the wall coercivity and results in predominantly re-entrant flux reversal.

A sampling optical microscope is integrated with computer controlled instrumentation and a digital image processor. The system is used to make quantitative measurements of magnetic domain wall motion. The system can measure the average stripe width, over an 8.7 micrometers length, with 0.003 micrometer precision and 2 ns temporal resolution. With this system, the threshold for horizontal Bloch line (HBL) nucleation and the coercivity of a vertical Bloch line (VBL) is measured in straight walls in bubble garnet material.

In magnetostrictive amorphous wires of composition (Fe77.5 Si7.5 B15) the process of domain collapse is an important ingredient of re-entrant reversal. During collapse, a narrow and high voltage pulse is generated due to the formation of an unstable domain. Experimental results showing the influence of an external magnetic field and an applied longitudinal tensile stress on the voltage pulse shape agree well with those calculated on the basis of an ellipsoidal domain model for the collapsing domain.

The dynamics of a magnetic domain wall containing vertical Bloch lines (VBL) has been investigated using numerical methods. The wall is of the kind found in thin film materials with a large anisotropy perpendicular to the plane of the film. The VBL's are all of the same chirality and are periodically repeated along the wall at equal spacing. The wall is driven by an applied field perpendicular to the film plane and the VBL's move gyrotropically. Both the wall and VBL's, starting from an equilibrium shape, soon attain a constant velocity. Distortion of the wall and structure from the equilibrium shape is evident and increases with field. The wall and VBL velocity both increase with field but neither are linear so that the ratio of VBL velocity to wall velocity decreases with applied field. For an applied field extrapolated to zero, the wall velocity agrees with the value predicted by the analytical rigid wall model and the ratio decreases by 50% for higher fields because of the distortion.

The effect of bias field upon stripe chopping margins in thin films with anisotropy perpendicular to the plane of the material has been investigated by numerical integration of the Landau-Lifshitz-Gilbert equation. The chopping margin increases with increasing bias field (corresponding to reduced initial wall-wall separation) when a uniform external field is applied. Horizontal Bloch line (HBL) formation is suppressed at large bias fields and this suppression is responsible for the large margin that is seen. When an external field typical of a conductor loop above the sample is used, the margins are significantly reduced. In this case, the structure of the wall is significantly more complex and multiple HBL's are frequently seen in the wall.