Obiettivo The ability to grow epitaxial thin films and multilayers to an extremely high quality is a prerequisite for the observation and understanding of new magnetic phenomena. The control and characterization of growth mechanisms, the initial stage of growth (nucleation) and the final multilayer structure are critical steps in the achievement of this objective. Multilayers have been prepared which exhibit either extremely high quality or comprise entirely new (metastable) phases.Iron/chromium is found to be a system of almost perfect lattice registry where coherent expitaxial growth occurs to considerable chromium and iron layer thicknesses. Multilayers and sandwiches of considerable perfection have been grown on lattice matched substrates (gallium arsenide and geranium).A wide variety of cobalt containing multilayers and sandwich structures have been prepared using primarily molecular beam epitaxy (MBE) techniques. Substrates have varied from mica and magnesium oxide to metallic single crystals such as platinum (100) and palladium (111). Buffer layers between substrate and multilayer have frequently been used to improve further the sample quality.A wide variety of samples have been prepared by MBE techniques with one or more of the layers grown in the form of a wedge of varying thickness. Examples are chromium wedges prepared on galliumarsenide/iron substrates, chromium manganese and copper wedges prepared on iron (100) single crystalline whiskers, cobalt wedges prepared on copper (100)/cobalt substrates. Thickness dependencies of structural (and magnetic) properties can be directly obtained from a single sample by means of position sensitive measurements such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED).A variety of techniques have been used to obtain structural information concerning the samples.The internal energy of a ferromagnet depends on the direction of the magnetization. The term in the total energy describing this is called the magnetic anisotropy energy. In the case of an interface the surface atoms are in a very different environment than the bulk atoms. This can create a large anisotropy for these atoms which is called the surface or interface anistrophy. Because of the importance of magnetooptical (MO) recording, the largest effort of researchers has been to create ultrathin layers in which spin orbit type anisotropies overcome the strong in plane shape anisotropy. It is the interface term which in some systems can induce the magnetization to orientate perpendicular to the film plane, a situation which is essential for MO recording media.A series of cobalt/X multilayers has been investigated, with X (equal to palladium, platinum, gold, silver, copper, iridium, molybdenum) being metals with widely differing lattice constants. No simple correlation was found between the strains induced in the cobalt layer by the lattice mismatch and the anisotropy in the multilayers. This suggests that the magnetostructure origin of anisotrophy (due to stress) is not the likely cause of interface anisotropy. Neel type anisotrophy originating from broken symmetry is the probable origin of perpendicular interface anisotropy.Perpendicular anisotropy has been determined in cobalt/ruthenium, cobalt/osmium, cobalt/nickel, cobalt/platinum and iron/silver multilayers and in ultrathin epitaxial cobalt films on palladium (111) single crystals. In the latter system a very large weakly temperature dependent interface anisotrophy was measured in the absence of linear strain. The temperature dependence of the anisotropy, in the iron/silver system, was close to the third power of the magnetization.Several established (volume selective magnetism (VSM), ferromagnetic resonance (FMR), superconducting quantum interface device (SQUID)) and new (Kerr loops, modified VSM) measure ment techniques have been employed to determine the anisotropy in the samples. A modification of a Kerr effect apparatus has made it possible to obtain a local measurement of magnetic anisotropy. This technique has been applied to a wedge formed cobalt/palladium (111) sample, whereby both interface and volume contributions to the anisotropy have been obtained from a single sample.The mechanism of the coupling of ferromagnetic layers through nonmagnetic interlayers has been investigated. Of special interest are the system iron/silver for which no antiferromagnetic (AF) type coupling has been reported, the system iron/chromium for which AF coupling is well established and the systems iron/copper and cobalt/copper which show weak AF type coupling. For cobalt/copper, in addition, a strong magnetoresistance (MR) effect was found. In the case of iron/chromium the relation between antiferromagnetic coupling and the grant magnestoresistive effect has been clarified.More details of the interlayer coupling for the iron/chromium/iron system have been revealed by Brillouin light scattering experiments. It appears that the coupling not only oscillates in magnitude or in function of the chromium interlayer thickness (with a period of 20 Angstrom) but also changes sign (from antiferromagnetic to ferromagnetic). The Neel temperature of the chromium was determined, by conversion electron Mossbauer spectrometry (CEMS), to be below room temperature, suggesting that the coupling may be through a paramagnetic chromium film.Several samples with layers deposited in the form of wedges have revealed extremely fine details in the oscillatory AF coupling. Additional short (approximately 2 monolayers) oscillatory periods have been discovered in the iron/chromium, iron/manganese, iron/gold, iron/copper and cobalt/copper systems. The structure of the copper interlayers of the latter 2 samples (iron/bcc copper and cobalt/fcc copper) is seen to totally change the oscillatory coupling. Longer oscillatory coupling periods have been determined in iron/aluminium and cobalt/ruthenium samples.Giant oscillating MR has been measured in cobalt/copper (111) and iron/copper (111) multilayers. In both systems the oscillating period is seen to be about 12.5 Angstrom but the phase is opposite. A maximum MR in cobalt/copper corresponds to a minimum in iron/copper. An MR ration of 8 0% has been measured in cobalt/copper multilayers with 10 Angstrom copper layers. Changing the growth direction of the cobalt/copper multilayers to (100) modifies the oscillatory period of the grant MR, in agreement with that observed in the coupling studies.The long oscillating period in both the AF coupling and MR can be theoretically modelled by a rather simple modification of the Rudermann-Kittel Kasuya-Yosida (RKKY) theory. The short and multiple oscillatory periods discovered in iron/copper and cobalt/copper can also be described within the bounds of a straightforward physical theory.The focus of work has been the preparation and characterization of metallic multilayers with unusual and intriguing magnetic properties, and the detailed understanding of the underlying physical mechanisms.The ability to grow epitaxial thin films and multilayers of an extremely high quality was a prerequisite for this work. Considerable ingenuity was also shown in the structural characterization of the samples with many techniques being used.The key issues studied in the field of magnetic anisotropy in magnetic multilayers are the differing contributions of volume and interface terms to the total anisotropy, and the origin of the interface term. It is the interface term which, in some systems, can induce the magnetization to orientate perpendicular to the film plane, which is essential for magnetooptical recording media.Magnetic interlayer coupling and magnetoresistance has also been studied. Of special interest are the iron silver systems, for which no antiferromagnetic (AF) type coupling has been reported, the iron chromium system, for which AF coupling is well established, and the iron copper and cobalt copper systems, which show weak AF type coupling. For cobalt copper, in addition a strong magnetoresistance effect was reported. The relation between, in the iron chromium case, AF coupling and the giant magnetoresistance effect had to be clarified quantitatively.The project is concerned with the growth and the study of physical properties of metallic magnetic superlattices. Six systems of primary interest have been selected: Co -Pd, Pt, Au, Cr and Fe - Cr, Ag. A fundamental understanding of the properties is of great significance for emerging applications of multilayers in areas like magnetic field sensors and recording media. The consortium combines existing experience in advanced UHV depostion with in-situ and ex-situ assessment techniques. Besides growth and the assessment of physical properties, the objectives are to gain insight into both the micro-magnetic structure and the magnetic order and finally to explore the possibility of new systems and effects in corresponding material systems. Campo scientifico natural scienceschemical sciencesinorganic chemistrytransition metalsnatural scienceschemical sciencesinorganic chemistryalkaline earth metalsnatural scienceschemical sciencesinorganic chemistrypost-transition metalsengineering and technologymaterials engineeringcoating and filmsnatural sciencesphysical sciencesopticsspectroscopy Programma(i) FP2-SCIENCE - Programme plan (EEC) to stimulate the international cooperation and interchange needed by European research scientists (SCIENCE), 1988-1992 Argomento(i) Data not available Invito a presentare proposte Data not available Meccanismo di finanziamento CSC - Cost-sharing contracts Coordinatore Nederlandse Philips Bedrijven BV Contributo UE Nessun dato Indirizzo 5600 MD Eindhoven Paesi Bassi Mostra sulla mappa Costo totale Nessun dato Partecipanti (5) Classifica in ordine alfabetico Classifica per Contributo UE Espandi tutto Riduci tutto Eindhoven University of Technology Paesi Bassi Contributo UE Nessun dato Indirizzo 2,Den Dolech 2 5600 MB Eindhoven Mostra sulla mappa Costo totale Nessun dato FORSCHUNGSZENTRUM JUELICH GMBH Germania Contributo UE Nessun dato Indirizzo WILHELM JOHNEN STRASSE 52425 JUELICH Mostra sulla mappa Collegamenti Sito web Opens in new window Costo totale Nessun dato Thomson-CSF Francia Contributo UE Nessun dato Indirizzo 173,Boulevard Haussmann 173 75415 Paris Mostra sulla mappa Costo totale Nessun dato UNIVERSITE DE PARIS-SUD XI Francia Contributo UE Nessun dato Indirizzo RUE GEORGES CLEMENCEAU 15 91405 ORSAY Mostra sulla mappa Costo totale Nessun dato UNIVERSITE LOUIS PASTEUR, STRASBOURG 1 Francia Contributo UE Nessun dato Indirizzo Rue Blaise Pascal 4 67070 STRASBOURG Mostra sulla mappa Costo totale Nessun dato
