FRACTAL ANALYSIS OF THE MAZE-LIKE DOMAIN STRUCTURE OF FERRITE-GARNET FILMS IN THE PROCESS OF MAGNETIZATION

В данной работе с использованием комплекса экспериментальных методик и специализированного программного обеспечения исследуются магнитные висмутсодержащие феррит-гранатовые пленки, выращенные на подложках из гадолиний-галлиевого граната. Методом оптической магнитометрии получены предельные петли магнитного гистерезиса для дефектных и бездефектных участков висмутсодержащих феррит-гранатовых пленок. Установлено, что вдали от дефектов петля демонстрирует бескоэрцитивное поведение в пределах погрешности. Для случая перемагничивания вблизи дефекта появляется коэрцитивное состояние с H~1 Э. Для разных участков предельной петли магнитного гистерезиса определена фрактальная размерность. Полученные значения лежат в диапазоне D=1,35÷1,46 для произвольного участка пленки и D=1,37÷1,54 для участка с дефектами. Определены типичные морфологические характеристики поверхности висмутсодержащей ферритгранатовой пленки. Полученные результаты позволяют для эпитаксиальных висмутсодержащих магнитных пленок феррит-граната прогнозировать взаимосвязь между значением намагниченности и значением фрактальной размерности. In this work, using a set of experimental techniques and specialized software, magnetic bismuth-containing ferrite-garnet films grown on gadolinium-gallium garnet substrates are investigated. The limiting magnetic hysteresis loops are obtained by the method of optical magnetometry for defective and defect-free areas of bismuth-containing ferrite-garnet films. It was found that, far from defects, the loop exhibits a non-coercive behavior within the error limits. For the case of magnetization reversal, a coercive state with H ~1Oe appears near the defect. For different sections of the limiting magnetic hysteresis loop, the fractal dimension is determined. The obtained values are in the range of D=1,35÷1,46 for an arbitrary section of the film and D=1,37÷1,54 for a section with defects. Typical morphological characteristics of the surface of a bismuth-containing ferrite-garnet film have been determined. The results obtained make it possible to predict the relationship between the value of magnetization and the value of fractal dimension for epitaxial bismuth-containing magnetic films of iron garnet.

Crystallization of Bi-substituted iron garnet bi-layers

Magneto-optical (MO) structures are widely used for different application in the fields of magnetoplasmonics, magneto-optics, photonics e.t.c. Bi-substituted iron garnet (Bi:IG) is high-performance MO material. Integration of Bi:IG films to silicon semiconductor technology gives new opportunities to create nanoscale hight performance MO devices. Vacuum sputtering deposition allows to fabricate Bi:IG structures on different substrate types. Authors investigate crystallization process of Bi:IG bi-layers in a different process parameter (different layers composition and its thickness, temperature and time of annealing) using gadolinium gallium garnet GGG and fused quartz SiO2 substrates to determine dependences which impact on crystallization.

Crystallization Double-Layer Magneto-Active Films for Magnetophotonics

Magneto-optics, magnetophotonics and magnetoplasmonics stay at the edge of scientific interests last years due to their unique features to manage the light and electromagnet field. Bi-substituted iron garnet (Bi:IG) is one of most promising magneto-optical material for these applications in order to its high efficiency in visible and infrared spectra. The possibility to integrate Bi:IG films to silicon semiconductor process leads to creation nanoscale hight performance magneto-optical devices. Bi:IG structures of different composition might be deposited by vacuum deposition on different substrates. The investigation of crystallization process of Bi:IG double-layer films at a different process parameter on gadolinium gallium garnet and fused quartz substrates allowing to determine dependences and suggestions for integration Bi:IG to semiconductor process or multicomponent optical nanostructures.

Study of soft photon yield in pp and AA interactions at JINR

Over 30 years there has been no comprehensive understanding of the mechanism of soft photons (energy smaller than 50 MeV) formation. Experimental data indicate an excess of their yield in hadron and nuclear interactions in comparison with calculations performed in QED. For a more thorough study of this phenomenon at the Nuclotron (a superconducting accelerator in JINR), preliminary measurements have been carried out with using an electromagnetic calorimeter based on BGO crystals. These results are consistent with the world data. In JINR, in connection with the building of a future accelerator complex NICA, it has become possible to carry out such studies in pp, pA and AA interactions at energies up to 25 A GeV. Our group develops the conception of an heterogeneous electromagnetic calorimeter as “spaghetti” and “shashlik” types based on gadolinium gallium garnet (GaGG) crystals with a low threshold for registration of photons. The first tests of prototypes of them manufactured at JINR on the basis of the GaGG and a mixture of tungstate and copper as an absorber are reported.