J. C. DeLuca

Effect of misorientation on growth anisotropy in [111]‐oriented garnet films

Phenomenological anisotropy constants have been measured in three garnet bubble films with their surface normal slightly misoriented from the crystallographic [111] direction. A tilted magnetic easy axis is found from measurements of homogeneous nucleation and bubble collapse in the presence of in‐plane fields. An in‐plane anisotropy is also found whose axes do not in general lie either normal to or in the easy‐axis tilt plane. These results are shown to be consistent with a phenomenological growth anisotropy model which includes the film plane misorientation.

Abstract: Bias field dependence of domain drag propagated bubble domains

Bubble propagation by the domain drag effect is studied as a function of bias field (Hb) in a GdCoAu amorphous film with pulse widths of 20, 40, and 50 ns and current densities in the 4×106 to 7×106 amp/cm2 range by pulsing currents directly through a stripline of amorphous material containing hexagonal arrays of bubbles. With 0<Hb<500 Oe the bubble velocity is largely independent of bias field remaining constant at a value of 65 m/sec; as the bias field is increased above 500 Oe the velocity decreases gradually through a minimum of 35 m/sec at 1100 Oe and then increases to 65 m/sec at Hb=1440 Oe.(AIP)

Laser annealing of epitaxial garnet films under controlled atmospheres

Epitaxial films with a composition of Eu0.54Y2.41Pb0.03Fe3.84Ga1.18O12 have been laser annealed in forming gas, nitrogen, air and oxygen. Annealed films were studied using bubble statics, ferromagnetic resonance and x‐ray techniques. Changes in the annealing ambient resulted in variations in the maximum saturation magnetization (4πMs) achieved, and in the laser power thresholds for film cracking and melting. In comparison with other atmospheres, oxygen allowed the use of greater laser power without film damage and yielded the highest saturation magnetization. The increase in 4πMs (above the as‐grown value) produced by annealing in oxygen was more than 30% larger than achieved in air and more than 50% larger than reached in forming gas or nitrogen. The influence of an ambient is interpreted in terms of its abbility to suppress the formation of oxygen vacancies during laser annealing.

Bias field dependence of domain drag propagation velocities in GdCoAu bubble films

The bias field dependence of the velocity of bubble propagation by the domain drag effect was studied in a GdCoAu amorphous film. Bubbles in close‐packed arrays were propagated by pulsing currents directly through a stripline of the material fabricated by photolithography and ion‐beam milling. As bias field is increased, at given current and pulse width, the velocity decreases, passes through a minimum, then increases again. The domain drag drive field at a given bias is derived both from the critical current at which motion begins and from the slope of velocity with current. A theory for the domain drag drive field Hd of a bubble raft with infinite length along the current direction is derived, giving the simple result Hd /βjD = 1/2(d0/D) −(π/4√3)(d0/D)3, where β is the Hall angle, j is the current density, d0 is the bubble diameter, and D is the nearest‐neighbor spacing. Experimental results from critical current agree approximately with the theory, but results from velocity slope with current are a fac...

The anisotropy dependence of bubble dynamics in EuGaYIG films

We have studied the dynamic properties of bubbles in a series of oxygen‐annealed EuGaYIG films which have similar magnetic properties except for decreasing uniaxial anisotropy as a function of anneal time. The translational saturation velocity and skew angle of bubbles translated in a pulsed gradient field experiment increase as the anisotropy decreases. These results are in agreement with theoretical predictions of a Ku−1/2 dependence. We also observe that for a given anisotropy and bubble state (S=1), the skew angle decreases as the drive increases, in agreement with theory which predicts that if the velocity is saturated, drive and angle are inversely related.

Dynamic properties of laser‐annealed, Ga‐substituted EuYIG bubble films

Laser annealing induced changes in Ga‐substituted EuYIG epitaxial bubble films were studied using FMR, bubble statics, SQUID magnetometry, and dynamic bubble translation experiments employing high speed photography. Comparing annealed to as‐grown films, domain wall mobility and saturation velocity were observed to increase up to 50% while static coercivity Hcs was reduced by as much as one‐third. Both an increase in exchange A and a decrease in damping α appear to contribute to enhanced mobility; we attribute the variations of both A and α to the interchange of Ga and Fe between crystal lattice sites brought about by laser annealing. The mechanism by which Hcs was reduced is less clear, but may follow from the reduction of stress during annealing.

Effect of large in‐plane fields on potential wells of bubbles under charged walls

At small values of in‐plane field Hp magnetic bubble domains can reside under charged walls at the edge of a nonimplanted disk. When Hp is increased along the charged wall and exceeds a critical value Hpcrit1, the stable bubble position moves many microns away from the disk. The maximum gradient of the well along this direction also goes to zero at this value, but the apparent field well depth Hw goes to zero at a lower value Hpcrit2. Between Hpcrit1 and Hpcrit2, Hw can actually be negative. A phenomenological theory is developed to show how this can occur. The maximum gradient of the well perpendicular to the charged wall is also studied. It is found to be asymmetric at low in‐plane fields, to decrease with increasing in‐plane field, and to be roughly a factor of two larger than the maximum gradient along the charged wall.

Elliptical distortion and bias compensation in the gradient propagation of bubble domains

Using high‐speed photography in a pulsed gradient field experiment we have studied the elliptical and radial distortion of bubble domains during propagation as a function of bias compensation, pulse width, and drive. We propose a theory which relates the gyrotropic forces exerted by the Bloch‐line pairs to the elliptical and radial distortion. As a function of bias compensation a peak appears in both the distortion and ballistic overshoot data at a point which closely coincides with the proper calculated value of bias compensation. The elliptical distortion and radial expansion at the peak are found to agree quite closely with theory at short pulse widths and low drives. At values of bias compensation different from the proper calculated value significant deviations from theory occur. In these cases the bubble losses its closely elliptical shape, becoming slightly asymmetrical, suggesting unequal generation of Bloch lines on its front and rear wall sections.

Size effects in Pb-alloy Josephson junctions

Five Pb‐alloy Josephson junctions of various sizes were fabricated together and variations in their electrical parameters were studied. The dependence of the excess current on the junction geometric dimensions is demonstrated. As the area to perimeter ratio of the junction is increased, there is a proportional decrease in excess current density. A simple analysis indicates that there is an insignificant contribution to excess current through the interior planar area of the junction with most of the excess current generated at the edges.