Eylem Seç
An electron microscope investigation of domain structures in gadolinium and terbium foils
Başlık:
An electron microscope investigation of domain structures in gadolinium and terbium foils
Yazar:
McKendrick, William H., author.
ISBN:
9780438060456
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (240 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: J. N. Chapman.
Özet:
This thesis contains a description of an electron microscope investigation of ferromagnetic domain structures in gadolinium and terbium foils. Up till now such an investigation has been prevented by the difficulties incurred in preparing these reactive metals in thin foil form and domain structure examinations have been limited to observations in bulk materials using methods which do not have the resolution capabilities of electron microscopy. In the present work ion beam thinning has been used to prepare foils of basal gadolinium and terbium as well as non-basal terbium with regions thin enough to permit a satisfactory examination of magnetic domains to be made. The Fresnel mode of Lorentz electron microscopy was used to show the domain wall regions as light and dark lines in the image plane whose intensity distributions yielded information on how the magnetisation varied in the foil. Because gadolinium and terbium are ferromagnetic only below room temperature a liquid nitrogen cooled specimen stage was employed which could, after modification, maintain a specimen at any temperature above 160K, In basal gadolinium a periodic domain structure was observed to form ~ 5K below the Curie temperature with a domain width which increased as temperature decreased, typically from about 50 nm to 90 nm at 160K, and decreased as the specimen was warmed up. Comparison of the observed structure with computed wall profiles suggested that the magnetization in the domain regions was at an angle to the foil normal between 30° and 70° depending on temperature and that the domain wall widths were a significant fraction of the domain widths. The existence of this periodic structure could not be explained by magnetocrystalline anisotropy alone because in gadolinium its effect is small. Therefore an additional anisotropy contribution was postulated. Domain energy models, both analytical and numerical were developed to account for observation but these incorporated one-dimensional magnetization distributions and a large additional uniaxial anisotropy was necessary to form the arrays of 180° Bloch-type models which were predicted to be energetically favourable. It was thought that the introduction of a two-dimensional model to reduce the surface magnetostatic energy of the one-dimensional distributions could also reduce the magnitude of the additional terra, and possible raeans of developing such a model was considered. The additional anisotropy term was also considered and from the information available it was thought that it originated from stresses in the foil. Basal terbium was only briefly examined because it was thought that the complex domain structures observed could have been strongly influenced by the annealing process used to prepare foils for ion beam thinning. Non-basal terbium foils displayed an irregular small scale domain structure which was quasi-periodic. However, this structure was related to a surface anomaly which had a direction parallel to the domain walls and which could have been caused by selective ion beam thinning along a given direction in the foil plane. This suggested that the effects of ion beam thinning should be carefully investigated in non-basal hexagonal materials such as terbium and gadolinium.
Notlar:
School code: 0547
Konu Başlığı:
Tüzel Kişi Ek Girişi:
Mevcut:*
Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684814.1) | 684814-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
On Order
Liste seç
Bunu varsayılan liste yap.
Öğeler başarıyla eklendi
Öğeler eklenirken hata oldu. Lütfen tekrar deneyiniz.
:
Select An Item
Data usage warning: You will receive one text message for each title you selected.
Standard text messaging rates apply.