Mark H. Kryder

A High Speed Magneto-Optic Camera System

A 7 nsec exposure time magneto-optic camera system has been constructed for observation of dynamic magnetic phenomena such as occurs in magnetic bubble domain devices. The system employs a super-radiant nitrogen pulsed dye laser as a light source, a polarizing microscope to make the magnetic features visible, and a low light level T. V. system for recording the observed phenomena. The laser pulse is synchronized within 1 nsec to the dynamic magnetic process to be observed and the video system framing rate may be synchronized to the laser so that each recorded video picture is a record of one instant in one dynamic process. A coil assembly and drive electronics were constructed to permit optical access to the magnetic sample and simultaneous application of high frequency (to 1 MHz) rotating magnetic fields (to 60 Oe) required to drive a bubble memory. To make the magnetic domains, which may be smaller than one micron, visible, polarizing optics and the Kerr or Faraday magneto-optic effects are employed. Techniques for optimizing the visibility of magnetic domains in such a system are discussed in detail. The system has made possible the visual observation of high speed magnetic bubble domain phenomena and has contributed significantly to the understanding of bubble domain dynamics.

Dynamics of 1μm bubbles in ion‐implanted contiguous disk structures

The dynamic behaviour of 1μm bubble domains in double‐layer garnet films in which the driving mechanism is by charged walls at ion‐implanted pattern edges has been investigated using a 7 nsec pulsewidth stroboscopic laser system. Bubble propagation around circular and square‐shaped structures, and between adjacent cusps forming part of a propagation loop was studied at frequencies up to 500 kHz. The data show that the tri‐directional magnetocrystalline anisotropy of the driving layer has a strong influence on the dynamic behavior of the bubbles and is necessary to explain observed dependences of bubble velocity on propagation direction. The effective mobility μeff, of the charged wall coupled to a bubble was measured and found to be linearly related to the ion‐implanted layer thickness t2, in agreement with theory. For a typical garnet composite of EuTmYGaIG/GdTmYGaIG with t2=0.4 μm, μeff∼280 cm/sec⋅Oe in comparison with a bubble domain wall mobility of ∼730 cm/sec⋅Oe. Expansion of domains along straight ...

Dynamic properties of charged walls in ion implanted garnets

The dynamic behavior of the charged wall in the ion implanted layer of contiguous disk bubble devices is determined for the first time without the disturbing influence of a bubble domain being coupled to the charged wall. The charged wall was stabilized next to a nonimplanted region by an applied in‐plane field Hx and was oscillated along ŷ by an rf field hy  sin ωt. Oscillations in Faraday magneto‐optic contrast signals proportional to the wall oscillations were detected with a high‐speed photomultiplier (PMT) when a focused laser beam was obliquely incident on the region of the charged wall. The drive frequency ω was provided by an rf tracking generator which was phase locked to a spectrum analyzer set to detect the fundamental amplitude response of the PMT signals. Our measurements were made on the doped yttrium iron garnet (YIG) layers Gd, Tm, Ga:YIG and Eu, Tm, Ga: YIG typically used for driving 5‐ and 1‐μm bubbles, respectively. The charged wall amplitude rolloff with frequency interpreted in terms ...

Influence of NiFe quality on bubble devices

It is anticipated that as the period of bubble devices decreases, undesired effects due to loss of permeability of the NiFe overlay will become increasingly important, even for half‐disk elements. The failure mechanism of ’’I‐bar crossing ’’ in H‐I tracks, which leads to high values of the minimum drive field Hxy(min), was studied for both 8 and 20 μm bubble periods as a means of gaining insight into such effects. Direct Ferrofluid observations, along with measurements of the parameter Hbb1 which characterizes the coercivity of an individual H bar, confirmed that the I‐bar crossing phenomenon originated in high coercivity, and hence high remanence and low permeability of the NiFe. This interpretation was supported by a study of the effects on a sample of a series of annealing treatments at increasing temperatures, a process known to increase NiFe coercivity. The annealing studies demonstrated that for a given NiFe thickness Hbbl was better correlated with Hxy(min) than was the sheet‐film coercivity Hc, sh...

Abstract: Magnetic properties and domain structures in narrow NiFe stripes

A large increase in coercivity and a small increase in the magnetoresistive effect, accompanying narrowing of stripes of Ni‐Fe films and decreasing film thickness, may be due to magnetization buckling perpendicular to the stripe length. Undesirable magnetic behavior may accompany decrease in size of Ni‐Fe magnetic bubble and recording head devices. (AIP)