Al és Ti alapú tömbi amorf és nanoszerkezetű kompozitok előállítása és vizsgálata = Preparation and investigation of Al and Ti based amorphous and nanocrystalline bulk comopsites

A Ti-Al alapú ötvözetek magas hőmérsékleten is nagy szilárdágú és kis sűrűségű szerkezeti anyagok. Az eddig használatos technológiák helyett, mi két új technológiát alkalmaztunk: az olvadékból való gyorshűtést és a mechanikai ötvözést. Sajnálatos módon Al-Ti alapú fémüveget nem sikerült előállítani, mert hiányzik a mély eutektikum a fázisdiagramban. Ezért csak a mechanikai ötvözés maradt és ezzel a módszerrel állítottunk elő egy sor amorf ötvözetet: Al50Ti50, Al50Ti45Ni5, Al50Ti40Ni10, Al55Ti35Cr15 és Al45Ti40Cr15. Ezeket az amorf porokat kompaktáltuk és különböző vizsgálatoknak vetettük alá. Kísérletek vannak folyamatban, hogy az amorf porokat magas hőmérsékletű védőbevonatként alkalmazzuk. Külön – külön, mind Al, mind Ti alapon lehet fémüveg szalagokat előállítani gyorshűtéssel. Mi az Al alapú fémüvegekre koncentráltunk. Az irodalomból ismert volt az általában ternér összetételű (Al85-92RE2-12Ni0-12) fémüveg, ahol a ritkaföldfém az amorfizáló ötvöző elem. Kísérletileg bizonyítottuk, hogy vannak más amorfizáló elemek is melyek a RE elemektől balra (Ca és Sr), jobbra (Nb és Ta) valamint alatta (Urán) helyezkednek el. Egy fontos, elektronszámhoz kötődő szabályt állapítottunk meg, miszerint a maximális szilárdságot e/a = 6,5 értéknél érjük el az egyfázisú amorf ötvözetek esetében. Azt találtuk, hogy Al-Ti alapon csak akkor kapunk nagyentrópiás ötvözetet, ha a 3d elemekből közel 50 at. % -ot adunk hozzá. 3 diplomamunka és egy PhD dolgozat készült el. | The Ti-Al alloys offer higher temperature capability along with low density and high stiffness. Instead of the usual technology, we have proposed two different routes based on melt spinning and mechanical alloying. Amorphous phase can not be obtained by rapid quenching from the melt due to the lack of deep eutectic, which prevent the sufficient under-cooling by melt spinning technique. This is why mechanical alloying has been used to prepare a series of Al-Ti based amorphous compositions: Al50Ti50, Al50Ti45Ni5, Al50Ti40Ni10, Al55Ti35Cr15, Al45Ti40Cr15. This amorphous powder have been compacted and investigated. Experiments are continuing to use this powder as wear and high temperature resistant coating material. Separately, both Ti and Al based amorphous ribbons can be obtained by melt spinning supposing that appropriate amorphous forming element are added. We have focused on Al based amorphous alloys extending the compositional area known in the literature and based on RE amorphizing elements (Al85-92RE2-12Ni0-12). We have proved that elements situated in the periodic table at the left (Ca and Sr), at the right (Nb and Ta) and below (U) to the RE elements are also amorphizing elements. An important electronic rule was established: for the one-phase amorphous alloys the maximal strength is achieved around e/a = 6.5. Al-Ti based high entropy alloys could be prepared with addition of more then 50 at% 3d elements. 3 diploma work and 1 PhD dissertations have been prepared

Preparation, structure and giant magnetoresistance of electrodeposited Fe Co/Cu multilayers

No systematic studies have been carried out on the giant magnetoresistance (GMR) of electrodeposited (ED) Fe-Co/Cu multilayers since the elaboration of a method for the optimization of the Cu layer deposition potential. In this paper, we present results on the electrochemical optimization of the Cu layer deposition potential which was found to depend on the relative iron concentration in the bath. An X-ray diffraction study of ED Fe5Co95(1.5 nm)/Cu(dCu) multilayers with dCu ranging from 0.8 nm to 10 nm revealed an fcc structure. For most of the multilayers, weak superlattice satellite reflections could be identified. The room-temperature magnetoresistance was studied in detail as a function of the individual layer thicknesses. Multilayers with Cu layer thicknesses above about 1.5 nm were found to exhibit a GMR behavior with a maximum GMR of about 5 % and a typical saturation field of 1 kOe. The GMR magnitude decreased with increasing Fe-content in the magnetic layer. The spacer layer thickness evolution of the MR data was established in detail after separating the ferromagnetic and superparamagnetic GMR contributions and no oscillatory GMR was found. A comparison with literature data on both physically deposited and ED Fe-Co/Cu multilayers is also made

Composition, morphology and electrical transport properties of Co-Pb electrodeposits

Bath compositions were elaborated for the codeposition of Co and Pb by taking into account the chemical compatibility of Co2+ and Pb2+ with the appropriate anions. Electrolytes containing either acetate, chloride or nitrate anions were tested, but only the acetate bath proved to be appropriate for the preparation of compact Co-Pb films. Deposits were obtained with constant current, with constant potential or by using various current and potential pulses in order to investigate the possibility of multilayer formation. The variation in deposit composition as a function of the deposition parameters was elucidated by using cyclic voltammetry, current transient measurements and gravimetry. X-ray diffraction (XRD) patterns recorded for two-pulse plated deposits revealed a nanocrystalline structure with grain sizes in the range 5 to 20 nm. The XRD peaks could be well indexed to pure face-centered cubic Co and Pb, indicating that the Pb codeposited with Co is not dissolved in Co but is segregated. Both the d.c.-plated and the two-pulse plated deposits exhibited anisotropic magnetoresistance without an indication for a noticeable giant magnetoresistance contribution. This means that the observed magnetoresistance arises from spin-dependent electron scattering events dominantly within the sufficiently large Co regions and not along electron paths between two Co regions via the Pb regions. Low-temperature resistivity measurements revealed a superconducting transition slightly below that of pure Pb. This may be ascribed to a proximity effect: the ferromagnetic Co grains suppress somewhat the superconductivity of the Pb phase due to the nanoscale phase mixture of the two constituents

Electrodeposition of Ni from various non-aqueous media: the case of alcoholic solutions

Although electrodeposition from aqueous media has been widely used to obtain metallic deposits, there are cases where the application of non-aqueous solutions offers advantages over the traditional baths or even represents the only way to electrodeposit some metals. For this reason, a study of the electrodeposition of Ni from various alcoholic solutions was performed. Apart from a detailed cyclic voltammetry study of these solutions, the surface morphology, crystal structure and texture as well magnetic properties of the deposits have also been investigated. The best results were obtained with methanol as solvent, so results on Ni deposits prepared from this solution will be presented in more detail whereas the case of the other alcoholic solutions investigated will be summarized only briefly. Structural and magnetic properties of the deposits obtained have been compared to literature data on Ni samples obtained from various non-aqueous solvents

Structure and giant magnetoresistance of electrodeposited Co/Cu multilayers prepared by two-pulse (G/P) and three-pulse (G/P/G) plating

The giant magnetoresistance (GMR) was investigated for electrodeposited Co/Cu multilayers. In order to better understand the formation of individual layers and their influence on GMR, multilayers produced by two different deposition strategies were compared. One series of Co(2 nm)/Cu(tCu) multilayers with tCu ranging from 0.5 nm to 6 nm was produced with the conventional two-pulse plating by using a galvanostatic/potentiostatic (G/P) pulse combination for the magnetic/non-magnetic layer deposition, respectively, whereby the Cu layer deposition was carried out at the electrochemically optimized potential. Another Co(2 nm)/Cu(tCu) multilayer series with the same tCu range was prepared with the help of a G/P/G pulse combination. In this latter case, first a bilayer of Co(2 nm)/Cu(6 nm) was deposited in each cycle as in the G/P mode after which a third G pulse was applied with a small anodic current to dissolve part of the 6 nm thick Cu layer in order to ensure the targeted tCu value. The comparison of the two series revealed that the G/P/G pulse combination yields multilayers for which GMR can be obtained even at such low nominal Cu layer thicknesses where G/P multilayers already exhibit bulk-like anisotropic magnetoresistance only. Surface roughness measurements by atomic force microscopy revealed that the two kinds of pulse combination yield different surface roughness values which correlate with the structural quality of the multilayers as indicated by the absence or presence of multilayer satellite reflections in the X-ray diffraction patterns. A separation of the superparamagnetic (SPM) contribution from the total observed GMR provided useful hints at the understanding of differences in layer formation between samples prepared with the two kinds of pulse combination. The results of multilayer chemical analysis revealed that mainly an increased Cu content of the magnetic layer is responsible for the onset of SPM regions in the form of Co segregations in the G/P/G multilayers with small Cu layer thicknesses. Magnetization measurements provided coercive force and remanence data which gave further support for the above interpretation of the GMR data

Magnetoresistance and structural study of electrodeposited Ni-Cu/Cu multilayers

Electrodeposition was used to produce Ni Cu/Cu multilayers by two-pulse plating (galvanostatic/potentiostatic control) from a single sulfate/sulfamate electrolyte at an optimized Cu deposition potential for the first time. Magnetoresistance measurements were carried out at room temperature for the Ni Cu/Cu multilayers as a function of the Ni Cu and Cu layer thicknesses and the electrolyte Cu2+ ion concentration. Multilayers with Cu layer thicknesses above 2 nm exhibited a giant magnetoresistance (GMR) effect with a dominating ferromagnetic contribution and with low saturation fields (below 1 kOe). A significant contribution from superparamagnetic (SPM) regions with high saturation fields occurred only for very small nominal magnetic layer thicknesses (around 1 nm). The presence of SPM regions was concluded from the GMR data also for thick magnetic layers with high Cu contents. This hints at a significant phase-separation in Ni-Cu alloys at low-temperature processing, in agreement with previous theoretical modeling and experiments. Low-temperature measurements performed on a selected multilayer down to 18 K indicated a strong increase of the GMR as compared to the room-temperature GMR. Structural studies of some multilayer deposits exhibiting GMR were performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of Ni Cu/Cu multilayers exhibited in most cases clear satellite peaks, indicating a superlattice structure which was confirmed also by cross-sectional TEM. The deterioration of the multilayer structure revealed by XRD for high Cu-contents in the magnetic layer confirmed the phase-separation concluded from the GMR data

Influence of Ag additive to the spacer layer on the structure and giant magnetoresistance of electrodeposited Co/Cu multilayers

In order to explore the possible surfactant effect of Ag on the formation of electrodeposited multilayers, Co/Cu(Ag) multilayers were prepared by this technique and their structure and giant magnetoresistance (GMR) were investigated. The multilayers were deposited from a perchlorate bath with various amounts of Ag+ ions in the solution for incorporating Ag atoms into the multilayer stack. Without Ag addition, secondary neutral mass spectroscopy (SNMS) indicated a well-defined composition modulation of the undermost Co/Cu bilayers. However, already at an Ag content as low as 1.8 at.% incorporated, SNMS showed a deterioration of the periodic multilayer structure. In agreement with the SNMS results, superlattice satellites were visible in the X-ray diffraction (XRD) patterns of the multilayers with up to 0.3 at.% Ag. The satellites were, however, very faint even for multilayers without Ag addition, indicating that the multilayers have high interface roughness and/or poor periodicity. In the absence of Ag and at the smallest Ag content investigated by XRD, a strong central multilayer peak and the weak superlattice satellites were complemented by weak diffraction maxima from non-periodic Co and Cu domains. In the Co/Cu(Ag) multilayer containing about 25 at.% Ag, i.e., nearly as much as Cu, XRD found a separate Ag(Cu) phase. In spite of the imperfect layered structure, a multilayer-type GMR behavior was observed in all samples up to about 10 at.% Ag incorporated in the multilayer stack. The GMR magnitude increased for Ag contents up to about 1 at.%, which implies that a small amount of Ag may have a beneficial effect through a slight modification of the layer growth and/or interface formation. However, for higher Ag contents beyond this level, the GMR was reduced in line with the structural degradation revealed by XRD and SNMS. For the highest Ag contents (above about 10 at.%), the GMR exhibited a behavior characteristic of a granular magnetic alloy, in agreement with the results of the structural study

Kontrollált precíziós elektrokémiai leválasztással készült bevonatok és nanostruktúrák vizsgálata = Investigation of deposits and nanostructures prepared by high-precision controlled electroplating

Elektrokémiai leválasztással Ni-Co és Ni-Cr ötvözeteket, Co-Cu/Cu és Co-Ni-Cu/Cu rétegpárokból álló multirétegeket, valamint Co-Cu(d1)/Cu(dCu)/Co-Cu(d2)/Cu(dCu) pszeudo-spinszelep szerkezeteket hoztunk létre. Vizsgáltuk a fenti struktúrák mágneses és magnetotranszport sajátságait. Részletesen elemeztük a Co-Cu/Cu multirétegek szerkezete és mágneses ellenállása közötti korrelációt a rézréteg vastagságának függvényében. A pszeudo-spinszelepek esetén a két mágneses réteg sajátságait külön-külön nem észleltük, hanem az átlagnak megfelelő mágnetotranszport viselkedést kaptunk. Elektrokémiai leválasztással kapott Ni-Co-Cu/Cu multirétegekben kimutattuk, hogy a bruttó Co:Ni arány változik a rétegvastagsággal. Ebből egyenetlen mélységi komonens-eloszlásra következtettünk, amit mélységprofil analízissel ki is mutattunk. A mélységprofil vizsgálatokat multirétegekben kb. 5 nm-es rétegvastagság-határig tudtuk kiterjeszteni. Bevezettük egy új, „reverz” mélységprofil-analízis technikát az elektrokémiai leválasztással kapott ötvözetek méységi komponens-eloszlásának méréséhez. Ezzel bizonyítottuk, hogy a mélységprofilok multirétegek esetén az összetételi moduláció és a felületi durvaság vastagsággal való növekedése miatt egyaránt változnak. A felületi érdesség figyelembe vételére számítási eljárást javasoltunk. A reverz mélységprofil technikával hordozó közeli oszcillációs jelenséget fedetünk fel Fe-Co-Ni ötvözetek egyenáramú leválasztása során. | Ni-Co and Ni-Cr alloys, Co-Cu/Cu and Co-Ni-Cu/Cu multilayers and Co-Cu(d1)/Cu(dCu)/Co-Cu(d2)/Cu(dCu) pseudo-spin valve structures were prepared by electrochemical deposition. Magnetic and magnetotransport properties of these structures were studied. The correlation between structural and magnetotransport properties of Co-Cu/Cu multilayers was analyzed in detail. For pseudo-spin valve structures, the properties corresponding to the layers of various thicknesses were not observed, but a magnetotransport behaviour for the average thickness was found. It was detected for electrodeposited Ni-Co-Cu/Cu multilayers that the overall Co:Ni ratio changes with the layer thickness. This led to the conclusion that the component distribution along the growth direction is uneven, which was directly detected by depth measurements. The depth profile analysis of the multilayers could be extended down to 5 nm layer thickness. We introduced the „reverse” depth profile analysis technique for the measurement of the in-depth component distribution in electrodeposited alloys. This helped to prove that the experimental depth profile data for multilayers depends on both the modulation of the components and the increase in surface roughness. A new calculation method was suggested to account for the change in deposit surface roughness in the calculation of depth profile data. We discovered the near-substrate composition oscillation in Fe-Co-Ni alloys electrodeposited with constant current

Óriás mágneses ellenállás (GMR) elektrolitikus multirétegekben = Giant magnetoresistance (GMR) in electrodeposited multilayers

Teljesültek a projekt fő célkitűzései az elektrokémiailag előállított (ED) és óriás mágneses ellenállást (GMR) mutató mágneses/nemmágneses multirétegek gócképződési és rétegnövekedési folyamatainak tanulmányozására vonatkozólag. Eddig kilenc folyóirat közlemény jelent meg, köztük egy összefoglaló cikk a Progress in Materials Science-ben, egy beküldött cikk elbírálás alatt van, további 5 cikk pedig előkészületben van. Az ED Co/Cu multirétegek nemmágneses rétegéhez adalékolt Pb, Bi és Ag elemek közül a Pb esetén találtunk javulást a GMR-ben. A fürdő hőmérsékletének nem volt jelentős hatása a GMR-re ED Co(-Ni)/Cu multirétegek esetén. Atomerő mikroszkópiával (AFM) vizsgáltuk a felületi durvaság és a GMR korrelációját ED Co/Cu mulitrétegeknél, különösen a rétegnövekedés kezdeti szakaszában, valamint különböző körülmények között készült ED Ni-Co/Cu multirétegekben. A korábban alig vizsgált ED Fe-Co/Cu multiréteg rendszerre részletesen meghatároztuk a GMR jelenség megfigyeléséhez szükséges előállítási körülményeket. Megmutattuk, hogy ED Co/Cu, Ni-Co/Cu and Fe-Co/Cu multirétegek esetén nincs oszcilláló viselkedése a GMR-nek a nemmágneses réteg függvényében. Mélységprofil analízissel megállapítottuk, hogy ED Fe-Co-Ni and Ni-Fe rétegekben spontán összetételfluktuáció alakul ki leválásnál a hordozó közelében. Modelleztük a GMR változását a mágneses tér függvényében, hogy jobban megérthessük a kísérletileg megfigyelt GMR görbéket. | The major planned tasks of the project aimed mainly at studying the nucleation and growth processes of electrodeposited (ED) magnetic/non-magnetic multilayers with giant magnetoresistance (GMR) behavior were accomplished. A total of 9 papers including a review in Progress in Materials Science have already been published, 1 paper is under review and 5 more papers are under preparation. As to the influence non-magnetic elements (Pb, Ag and Bi) in the spacer layer on GMR in ED Co/Cu multilayers, a beneficial effect was found in the case of Ag. No significant influence of bath temperature on GMR could be demonstrated for ED Co(-Ni)/Cu multilayers. Atomic force microscopy (AFM) was used to investigate the surface roughness and its correlation with GMR in ED Co/Cu multilayers especially in the early stages of multilayer formation and in ED Ni-Co/Cu multilayers prepared under various conditions. The electrochemical preparation conditions for observing GMR were elaborated in detail for ED Fe-Co/Cu multilayers rarely investigated before. It could be shown that the GMR does not exhibit an oscillatory behavior as a function of the spacer layer thickness for ED Co/Cu, Ni-Co/Cu and Fe-Co/Cu multilayers. Depth profiling studies revealed a spontaneous composition vairation in the near substrate zone of ED Fe-Co-Ni and Ni-Fe layers. The magnetic field dependence of the GMR was modelled in order to better understand the experimentally observed GMR curves in multilayers

Influence of Pb additive to the spacer layer on the structure and giant magnetoresistance of electrodeposited Co/Cu multilayers

In an effort to see the possible surfactant effect of Pb on the formation of electrodeposited multilayers, Co/Cu(Pb) multilayers were prepared by this technique and their structure and giant magnetoresistance (GMR) were investigated. The multilayers were deposited from a perchlorate bath with various amounts of Pb2+ ions in the solution. The composition analysis by energy dispersive X-ray spectroscopy revealed that the Pb mole fraction in the deposit varies in a non-monotonous manner with Pb2+ ion concentration. By fitting the measured X-ray diffraction patterns, superlattice satellites could be identified in some of these multilayers. A ferromagnetic-type GMR behavior was observed for Co/Cu(Pb) deposits prepared from baths with small Pb2+ ion concentration, corresponding to the formation of a layered structure. The GMR magnitude decreased from 8 to 10 % with increasing Pb concentration and, also, changed to a superparamagnetic-type GMR; finally, for high Pb2+ ion concentrations, the magnetoresistance behavior turned over to anisotropic magnetoresistance characteristic of bulk materials