Buffer influence on magnetic dead layer, critical current and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

We present a thorough research on Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of MTJs, such as critical switching current and thermal stability. We investigate devices consisting of buffer/FeCoB/MgO/FeCoB/Ta/Ru multilayers for three different buffers: Ta 5 / Ru 10 / Ta 3, Ta 5 / Ru 10 / Ta 10 and Ta 5 / Ru 20 / Ta 5 (all thicknesses in nm). In addition, we study systems with a single FeCoB layer deposited above as well as below the MgO barrier. The crystallographic texture and the roughness of the buffers are determined by means of XRD and atomic force microscopy measurements. Furthermore, we examine the magnetic domain pattern, the magnetic dead layer thickness and the perpendicular magnetic anisotropy fields for each sample. Finally, we investigate the effect of the current induced magnetization switching for nanopillar junctions with lateral dimensions ranging from 1 {\mu}m down to 140 nm. Buffer Ta 5 / Ru 10 / Ta 3, which has the thickest dead layer, exhibits a large increase in the thermal stability factor while featuring a slightly lower critical current density value when compared to the buffer with the thinnest dead layer Ta 5 / Ru 20 / Ta 5

Study of Spin-Orbit Interactions and Interlayer Ferromagnetic Coupling in Co/Pt/Co Trilayers in Wide Range of Heavy Metal Thickness

The spin-orbit torque, a torque induced by a charge current flowing through the heavy-metal conducting layer with strong spin-orbit interactions, provides an efficient way to control the magnetization direction in heavy-metal/ferromagnet nanostructures, required for applications in the emergent magnetic technologies like random access memories, high-frequency nano oscillators, or bio-inspired neuromorphic computations. We study the interface properties, magnetization dynamics, magnetostatic features and spin-orbit interactions within the multilayer system Ti(2)/Co(1)/Pt(0-4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by optical lithography on micrometer-sized bars. In the investigated devices, Pt is used as a source of the spin current and as a non-magnetic spacer with variable thickness, which enables the magnitude of the interlayer ferromagnetic exchange coupling to be effectively tuned. We also find the Pt thickness-dependent changes in magnetic anisotropies, magnetoresistance, effective Hall angle and, eventually, spin-orbit torque fields at interfaces. The experimental findings are supported by the relevant interface structure-related simulations, micromagnetic, macrospin, as well as the spin drift-diffusion models. Finally, the contribution of the spin-orbital Edelstein-Rashba interfacial fields is also briefly discussed in the analysis.Comment: 39 pages, 14 figure

Dyfrakcja rentgenowska na układach wielowarstwowych : metody pomiaru i modele : praca doktorska /

Recenzenci pracy: Grzegorz Gładyszewski, Wojciech Łużny.Praca doktorska. Akademia Górniczo-Hutnicza im. Stanisława Staszica (Kraków), 2006.Bibliogr. k. 114-118.Dyfrakcja rentgenowska na cienkich warstwach, dyfraktometr X’Pert MPD, geometrie pomiarów, pomiary w geometrii Bragga-Brentana, wiązki równoległej, układy szczelin formujące wiązkę pierwotną, wtórną, rodzaje pomiarów dyfrakcyjnych w badaniach cienkich warstw, pomiar 0-20, 20, ω, figury biegunowe, reflektometria, podstawy teoretyczne dyfrakcji, wytwarzanie próbek, etapy wytwarzania złącza tunelowego, nanoszenie warstw metodą rozpylania jonowego, utlenianie bariery, wygrzewanie, litografia optyczna, wytrawianie jonowe, metody pomiaru własności magnetycznych, elektrycznych, topografii powierzchni, magnetorezystancji tunelowej, pętli magnetycznych, magnetometr Kerra, pomiar topografii powierzchni, mikroskop sił atomowych, periodyczne układy wielowarstwowe typu supersieci, dyfrakcja na periodycznej strukturze wielowarstwowej, modele teoretyczne, analityczny, symulacyjny, na układzie (Fen/Aun)xN, struktura warstwowa próbek, model układu periodycznego o niecałkowitym zapełnieniu warstw, porównanie wyników modelu z rzeczywistym układem Fe/Au, nieperiodycznych układów wielowarstwowych, struktury wielowarstwowej, obliczanie profilu 0-20, przykładowe symulacje, złącze tunelowe typu zawór spinowy, zawór spinowy, magnetyczne złącze tunelowe, sprzężenia magnetyczne w złączu, pola przełączeń, sprzężenie międzywarstwowe FP-S-FF, kontaktowe AF-FP, wpływ warstw buforowych na mikrostrukturę, własności złącz tunelowych, struktura złącza tunelowego typu zawór spinowy, badanych złącz, pomiary dyfrakcyjne, symulacja profili 0-20 złącz tunelowych z różnymi buforami, wpływ tekstury, szorstkości na własności magnetyczne, elektryczne, magnetorezystancja tunelowa, złącza tunelowe ze zmienną grubością warstwy swobodnej, programy napisane w ramach pracy doktorskie

Surface-Step-Induced Magnetic Anisotropy in Epitaxial LSMO Deposited on Engineered STO Surfaces

Changes in stoichiometry, temperature, strain and other parameters dramatically alter properties of LSMO perovskite. Thus, the sensitivity of LSMO may enable control of the magnetic properties of the film. This work demonstrates the capabilities of interface engineering to achieve the desired effects. Three methods of preparing STO substrates were conducted, i.e., using acid, buffer solution, and deionized water. The occurrence of terraces and their morphology depend on the preparation treatment. Terraces propagate on deposited layers and influence LSMO properties. The measurements show that anisotropy depends on the roughness of the substrate, the method of preparing the substrate, and oxygen treatment. The collected results suggest that the dipolar mechanism may be the source of LSMO anisotropy

Investigation of Dye Dopant Influence on Electrooptical and Morphology Properties of Polymeric Acceptor Matrix Dedicated for Ternary Organic Solar Cells

The publication presents the results of investigations of the influence of dye dopant on the electrooptical and morphology properties of a polymeric donor:acceptor mixture. Ternary thin films (polymer:dye:fullerene) were investigated for potential application as an active layer in organic solar cells. The aim of the research is to determine the effect of selected dye materials (dye D131, dye D149, dye D205, dye D358) on the three-component layer and their potential usefulness as an additional donor in ternary cells, based on P3HT donor and PC71BM acceptor. UV–vis spectroscopy studies were performed, and absorption and luminescence spectra were determined. Ellipsometry parameters for single dye and ternary layers have been measured. The analyses were performed using the Raman spectroscopy method, and the Raman spectra of the mixtures and single components have been determined. Organic layers were prepared and studied using scanning electron microscope and atomic force microscope. For dyes, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy studies were carried out and the ternary system was presented and analyzed in terms of energy bands

Nitrogen Dioxide Sensing Using Multilayer Structure of Reduced Graphene Oxide and α-Fe₂O₃

Multilayers consisting of graphene oxide (GO) and α-Fe2O3 thin layers were deposited on the ceramic substrates by the spray LbL (layer by layer) coating technique. Graphene oxide was prepared from graphite using the modified Hummers method. Obtained GO flakes reached up to 6 nanometers in thickness and 10 micrometers in lateral size. Iron oxide Fe2O3 was obtained by the wet chemical method from FeCl3 and NH4OH solution. Manufactured samples were deposited as 3 LbL (GO and Fe2O3 layers deposited sequentially) and 6 LbL structures with GO as a bottom layer. Electrical measurements show the decrease of multilayer resistance after the introduction of the oxidizing NO2 gas to the ambient air atmosphere. The concentration of NO2 was changed from 1 ppm to 20 ppm. The samples changed their resistance even at temperatures close to room temperature, however, the sensitivity increased with temperature. Fe2O3 is known as an n-type semiconductor, but the rGO/Fe2O3 hybrid structure behaved similarly to rGO, which is p-type. Both chemisorbed O2 and NO2 act as electron traps decreasing the concentration of electrons and increasing the effective multilayer conductivity. An explanation of the observed variations of multilayer structure resistance also the possibility of heterojunctions formation was taken into account