Dynamic Bubble Collapse Research Articles

Statics and dynamics of hard wall in a 1 mu m bubble material

The static and dynamic characteristics of the vertical Bloch lines (VBLs) and their stability are studied for a typical 1- mu m bubble material. The measured static bubble collapse fields H/sub c/ and the width of the bias pulse field necessary for dynamic bubble collapse are reasonably explained by assuming the critical hard wall energy of 1.1 erg/cm/sup 2/. The VBLs are found to be stable for the 10/sup 7/ applications of a series bias pulse field of 80 Oe amplitude at room temperature. >

Domain wall mobility in rare earth-transition metal alloys

The domain-wall mobility of amorphous alloys of rare-earth-transition-metal thin films has been measured at high temperatures (50 to 200 degrees C) by means of the dynamic bubble collapse method for TbCo, GdCo, GdTbCo, TbFeCo, GdTbFe, and GdTbFeCo. It is found that the domain-wall velocity is linearly proportional to the applied field if the field is significantly larger than the coercivity. The values of the mobilities range from 0.9 to 29 cm/s-Oe. The mobility increases slightly with temperature in the range of 50-200 degrees C. These data are in agreement with the fact that mobility is linearly related to the domain-wall width, which in turn increases in this temperature range because of the rapidly decreasing anisotropy. It is also found that mobility depends on the composition. Increasing the ratio of Gd to Tb significantly raises the value of the mobility.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer Simulation of Dynamic Magnetic Bubble Collapse

A computer simulation of magnetic domain wall motion was performed in order to study the dynamic bubble-collapse process under a wide range of drive fields. An unichiral bubble with a circular symmetry in a garnet film was assumed for simplifying the computation. The instantaneous bubble radius, horizontal Bloch line propagation, and wall overshoot effect were studied as well as the time-averaged wall velocity during the collapsing process. The time-averaged velocity of the bubble wall was compared with the results of the simulated velocity of a plane wall and the velocity measured in the dynamic bubble collapse experiment. There was a fair agreement among these velocities, but a slight difference in saturation velocity between bubble wall and plane wall was found. It originated from a difference in the surface stray in-plane field for these two geometries.

Nucleation and Punch-Through of a Horizontal Bloch Line Detected in Dynamic Bubble Collapse

The radial wall motion in an ion-implanted garnet film is investigated by using dynamic bubble collapse and chirality switching measurements. Experimental results at low drive fields are explained well in terms of the motion of a horizontal Bloch line (HBL). Chirality switching occurs during the punch-through of the HBL when ψ̄ reaches π. Two types of velocity peaks are detected in the dynamic bubble collapse experiments of x+ bubbles. As compared with the results of the chirality switching measurements, these two peaks are considered to correspond to the nucleation and the punch-through of a HBL, respectively.

Bubble states in a contiguous disk magnetic bubble device

Bubble states in a contiguous disk 2-μm bubble device have been studied using the dynamic bubble collapse method. We found at least three different bubble states, and two of them, soft and hard bubbles, showed 12.4 Oe of bias field margin for dynamic bubble collapse discrimination. The bubble state stability studied for a 100-Hz drive in-plane field appears fair, suggesting that the wall encoding scheme is also possible as in the conductor drive or Permalloy bubble devices. The wall structure of these three kinds of bubbles are discussed, and appears to be S = 1/2 (hard), S = (122) (soft), and S = 1H (intermediate), all having an umbrella cap.

Nondestructive sensing of wall-state transition and a dynamic bubble collapse experiment

The dynamic bubble collapse method was used to detect the oscillatory wall motion displacement versus pulsewidth or pulse field strength in low damping as-grown garnet film. It had been speculated that the nondestructive sensing of the bubble state after bias pulsing would provide important information about bubble dynamics. The method of nondestructive sensing for the χ bubble state is based on the principle of "in-plane automotion," and for the σ bubble states, on "automotion II." Because four kinds of bubbles having the same revolution number S = 1 move in different directions for a single combination of in-plane dc field and orthogonal in-plane pulse field having a fast rise-time and slow fall-time pulse shape, the strip line and the optical microscope TV system enable the observer to distinguish among four kinds of bubble states. The transition probability versus the bias pulse field experiment shows that the first transition is clearly demonstrated for the fast fall-time bias pulse, and that the transition process ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\chi+ \rightarrow \chi- \rightarrow \chi+ \rightarrow \chi-</tex> ) occurs in sequence for increasing bias pulse field and for increasing bias pulsewidth in the case of slow fall-time.

Discrimination of domain wall states by bubble collapse time

The discrimination of bubble states by dynamic bubble collapse was studied for 5 and 3 μm bubble films. We obtained bias field margin of 6 Oe for the 5 μm bubble film (S=1H and S=0), and about 10 Oe for 3 μm bubble films (S=1H and S= (120)). The discrimination was also tried for 3 μm bubble YY-propagation pattern chips, for which we got about 8 Oe of bias field margin. Demonstrated was this collapse discrimination for ’’1111...’’ ’’0000...’’, and ’’1010...’’ bubble patterns utilizing an on-chip bubble annihilator.

Discrimination of S = 1 and S = 0 bubbles by dynamic bubble collapse

The dynamic bubble collapse characteristics of S = 1 and S = 0 bubbles in ion-implanted films have been studied in the presence of a moderate in-plane field. The influence of the pulse shape and in-plane field has been measured in detail, and the results demonstrate that S = 1

Discrimination and state stability of S=1 and 0 bubbles in a field access racetrack

Discrimination of S=1 and 0 bubbles using dynamic bubble collapse and a state-stability test under quasistatic translation were tried for a YY-pattern racetrack on a 3-μm bubble film with a YIG capping layer. The bias-field margin for collapse discrimination was 5 Oe. These two states were stable for 140–160 Oe of bias field and for 25–50 Oe of rotating in-plane field.

Abstract: Detection of Walker oscillation by dynamic bubble collapse method in garnet material

Abstract: Detection of Walker oscillation by dynamic bubble collapse method in garnet material

New bubble materials with high peak velocity

Peak velocities higher than 40000 cm s-1and domain wall mobilities of the order of 1500 cm s-1Oe-1were measured by the dynamic bubble collapse method in garnet films having an orthorhombic anisotropy. The orthorhombic anisotropy was realized by growing garnet films with positive magnetostriction constants under strong compression on

Theory of saturation velocity and ballistic overshoot for interpreting domain wall oscillation and dynamic bubble collapse experiments in high mobility bubble films

A theory is presented for the interpretation of domain wall oscillation and dynamic bubble collapse experiments in high mobility bubble materials. The theory is based on Slonczewski's equations of motion for x, the normal wall coordinate, and ψ , the average procession angle of the wall spins. The wall velocity is assumed to be saturated at a constant value for all ψ > 0 , as proposed in an earlier treatment of bubble propagation experiments. The theory predicts oscillations of a wall in a potential well in response to a step or pulse of drive field. The oscillations are radically different from those of an underdamped h harmonic oscillator because they arise from a nonlinear ballistic overshoot effect. Oscillation periods are orders of magnitude larger than those predicted from Döring's classical theory. The periods increase with increasing drive and decrease with increasing period number. The oscillations are typically triangular as a function of time and the oscillation peak die away faster than linearly. These predictions are shown to be in reasonable quantitative agreement with data by Brown et al. and by de Leeuw and Robertson. Applied to the case of dynamic bubble collapse, the theory predicts multiple, sharp peaks in the apparent velocity versus drive curve. If πμ γ ⪢ χ c , where μ is the linear mobility, γ is the gyromagnetic ratio and x c is the distance the wall must go to reach the dynamic collapse radius, very large apparent velocities are shown to be possible, even though the actual saturation velocity may be small. Furthermore, dynamic penetration of the bubble's potential barrier is predicted, i.e. a bias field less than that required for quasistatic collapse can dynamically collapse the bubble. These characteristics are identified semiquantitatively in the earlier experimental data of the author.

Mobility of bubbles with small numbers of Bloch lines

The translational and radial mobilities of bubbles with small numbers of Bloch lines are investigated in a garnet film with moderately low damping. Depending on the number of Bloch lines, the bubbles propagate at different angles in an applied field gradient, in agreement with previous theory. However, the dependence of translational speed on Bloch line number, though weak, is an order of magnitude larger than predicted unless one attributes an additional coercivity or viscous damping to each Bloch line. Bubbles whose states have been identified by propagation in a gradient field are investigated by the dynamic bubble collapse technique; the ones which deflect at a particular nonzero angle show the largest dynamic collapse velocities. This experiment gives evidence that these bubbles, rather than those showing no deflection, are the ones without any Bloch lines. Such bubbles are investigated over a large range of radial drive fields; they show an initial high-mobility region culminating in a sharp peak, followed by a region of lower but appreciable mobility, followed by a velocity saturation. These features are compared to a theory by Slonczewski. In addition it is shown that the dynamic bubble collapse technique can be extended and its analysis simplified by working at very small threshold fields.