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X-ray speckle experiments on the per...

Pierce, Michael Scott.

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X-ray speckle experiments on the persistence and disintegration of magnetic memory.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	X-ray speckle experiments on the persistence and disintegration of magnetic memory./
作者:	Pierce, Michael Scott.
面頁冊數:	214 p.
附註:	Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3859.
Contained By:	Dissertation Abstracts International67-07B.
標題:	Physics, Electricity and Magnetism. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3224276
ISBN:	9780542772924

X-ray speckle experiments on the persistence and disintegration of magnetic memory.
Pierce, Michael Scott.

X-ray speckle experiments on the persistence and disintegration of magnetic memory. - 214 p.

Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3859.

Thesis (Ph.D.)--University of Washington, 2006.

Beautiful theories based on random microscopic disorder have been developed over the past ten years. My goal was to directly compare these theories with precise experiments. To do so, I first developed and then applied coherent x-ray speckle metrology to a series of thin multilayer perpendicular magnetic materials. To directly observe the effects of disorder, increasing degrees of disorder was deliberately introduced into a series of magnetic films. I used coherent x-rays, produced at the Advanced Light Source at Lawrence Berkeley National Laboratory, to generate highly speckled magnetic scattering patterns. The scattering patterns provided both the ensemble average characteristics of the magnetic domains, but were also directly sensitive to the microscopic magnetic domains. The apparently "random" arrangement of the speckles is due to the exact configuration of the magnetic domains in the sample. In effect, each speckle pattern acts as a unique fingerprint for the magnetic domain configuration. Small changes in the domain structure change the speckles, and comparison of the different speckle patterns provides a quantitative determination of how much the domain structure has changed. My experiments quickly answered one longstanding question: How is the magnetic domain configuration at one point on the major hysteresis loop related to the configurations at the same point on the loop during subsequent cycles? This is called microscopic return point memory (RPM). I found the RPM is partial and imperfect in the disordered samples, and completely absent when the disorder was not present. I also introduced and answered a second important, new question: How are the magnetic domains at one point on the major hysteresis loop related to the domains at the complementary point, the inversion symmetric point on the loop, during the same and during subsequent cycles? This is called microscopic complementary point memory (CPM). I found the CPM is also partial and imperfect in the disordered samples and completely absent when the disorder was not present. In addition, I found that the RPM is always a little larger than the CPM. I also studied the correlations between the domains within a single ascending or descending loop. This is called microscopic half-loop memory (HLM). I found an important relationship between disorder and the rate at which the domain configuration changes. Increasing disorder results in more rapid changes in the configuration along a single, half sweep from saturation to reversal. In addition to the coherent scattering results, I also studied the ensemble average behavior of the samples and how they are influenced by disorder. Disorder was found to greatly influence the ordering and length scales present in the domain configurations. At the time, no existing theory was capable of reproducing all these experimental results within one framework. Indeed, the RPM > CPM > 0 result was not predicted by any theory. So, working with theorists, we developed new theoretical models that do fit my experiment. These experimental and theoretical results have set new benchmarks for future work.

ISBN: 9780542772924Subjects--Topical Terms:

1019535
Physics, Electricity and Magnetism.

X-ray speckle experiments on the persistence and disintegration of magnetic memory.
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