Study of techniques for the reduction of creep in plated wire memories Final report, 28 Jun. 1967 - 28 Aug. 1968

Magnetization reversal in thin films of plated wire memory element

Dynamique d'aimantation dans les jonctions tunnels magnétiques à anisotropie perpendiculaire

Epitaxial (MgO barrier) magnetic tunnel junctions (MTJs) are the most promising systems for applications ranging from high performance recording heads to magnetic random access memories (MRAM). Besides, such junctions also involves new and fascinating physics, such as the physics of electronic transport across epitaxial barriers, or the physics of magnetic coupling across a thin barrier. We described results obtained on MTJs perpendicular FePt/MgO/FePt magnetization. Far less studied, systems with perpendicular magnetization may have the highest potential for use at the highest recording densities in MRAM. We demonstrated that high magnetic anisotropy - L10 phase FePt layers can be grown in FePt/MgO/FePt trilayers, spontaneously with one soft and one hard layer. In addition, full magnetic decoupling is obtained in spite of the large magnetization of both layers. The manuscript then focuses on two studies. First, we observe the domain wall propagation speed on FePt single layers, as a function of both the applied field and of the layer thickness (from 2 to 6 nm), thereby extending the studies previously limited to ultrathin Pt/Co/Pt films to non-zero thicknesses. Second, we observed in details the magnetic coupling phenomena between the two FePt layers in full MTJs. By combining magneto-optical (macroscopic) studies and Magnetic Force Microscopy imaging, we gained a detailed understanding of the origin of the coupling, and of the process by which the cycling of the soft layer can induce a progressive demagnetization of the hard one.Les jonctions tunnel magnétiques (JTM) épitaxiées à barrière MgO constituent probablement le système le plus prometteur pour des applications allant depuis les têtes de lecture des disques durs jusqu'aux mémoires magnétiques à accès aléatoire. De plus, de telles jonctions mettent en jeu une physique nouvelle et fascinante, celle de la physique du transport électronique au travers de barrières épitaxiées, ou du couplage magnétique entre électrodes au travers d'une fine barrière. Nous présentons des travaux conduits sur des jonctions à perpendiculaire (FePt/MgO/FePt). Très peu étudiés, les systèmes à aimantation perpendiculaire semblent présenter le potentiel le plus élevé aux très hautes densités dans les mémoires MRAM. Nous avons montré que des jonctions FePt/MgO/FePt peuvent être obtenues avec des couches de FePt chimiquement ordonnées dans la phase L10 de très forte anisotropie magnétocristalline. Ces jonctions présentent spontanément une couche dure et une couche douce, et un découplage magnétique en dépit de la forte aimantation volumique de l'alliage FePt. La thèse porte alors principalement sur deux études : - la propagation de parois dans des films minces de FePt, en fonction du champ appliqué et de l'épaisseur de la couche mince (entre 2 et 6 nm). Nous étendons ici les études auparavant réalisées dans la limite de films ultra-minces (Pt/Co/Pt)/ - les phénomènes de couplage magnétique entre électrodes à aimantation perpendiculaire dans la jonction complète. En combinant études macroscopiques (magnéto-optiques) et locales, nous proposons une description détaillée de l'origine du couplage magnétique, et du processus qui peut conduire à la démagnétisation progressive de la couche dure lors du cyclage de la couche douce

Computer-aided electronic circuit design, part I. Conduction processes in thin films, part II Status report, 1 Jun. - 30 Nov. 1965

Computer-aided electronic circuit design, and conduction processes in thin film

Spin wave propagation in structures with locally modified magnetic anisotropy

Zařízení založená na spinových vlnách mají potenciál být využita ve výpočetní technice s nízkou spotřebou energie. Pro úspěšné využití je samozřejmě potřeba spojit více takových zařízení na jednom čipu, součástí čehož musí být zatáčení spinových vln zahnutými vlnovody. Problém zatáčení spinových vln v dipolárně výměnném režimu zatím nebyl uspokojivě vyřešen, vyzkoušené přístupy vedly ke ztrátě intenzity a fázové koherence. V této diplomové práci jsme zkoumali dva systémy, které by mohly být využity k zatáčení spinových vln. Prvním z nich jsou tenké metastabilní vrstvy slitiny železa a niklu. Paramagnetická metastabilní fcc vrstva, která byla epitaxně narostena na substrátu z mědi, může být transformována do stabilní ferromagnetické bcc fáze pomocí fokusovaného iontového svazku. Tato technika nám dává prostorovou kontrolu nad transformačním procesem a strategie skenování svazkem nám dokonce umožňuje určit směr mangetické anisotropie. Magnetické vlastnosti struktur vytvořených touto metodou a lom spinových vln mezi doménami s odlišným směrem magnetické anisotropie byly změřeny pomocí mikroskopie Brillouinova rozptylu světla. Druhým zkoumaným systémem jsou zvlněné vlnovody, jejichž zvlnění indukuje magnetickou anisotropii. Zvlnění magnetické vrstvy je vytvořeno depozicí nemagnetických vlnek na substrátu indukovanou fokusovaným elektronovým svazkem a následnou depozicí magnetického materiálu. Byly vyrobeny různé návrhy zatočených zvlněných vlnovodů a změřili jsme šíření spinových vln jejich zatáčkami pomocí mikroskopie Brillouinova rozptylu světla. Využili jsme také mikromagnetické simulace pro získání hlubšího porozumění zkoumané problematiky a pro hledání vhodných návrhů experimentů.Devices based on spin waves have the potential to be used in low-power data processing. Naturally, a successful application would require many of those devices to be interconnected on a chip. Such a chip would have to include steering of spin waves through turned waveguides. The issue of steering dipole-exchange spin waves through waveguides has not been sufficiently solved so far, as the tested designs lead to a loss of intensity and phase coherence. In the presented thesis, we have studied two systems, which could be exploited for spin-wave steering. First, we dealt with metastable iron-nickel thin films. The paramagnetic metastable fcc layer epitaxially grown on a Cu substrate can be transformed into a stable ferromagnetic bcc phase by a focused ion beam. This technique gives us spatial control over the transformation process, and the scanning strategy even allows us to determine the direction of magnetic anisotropy. Magnetic properties of structures prepared by this technique, together with spin-wave refraction between domains with different anisotropy directions, were characterized by Brillouin light scattering microscopy. Moreover, we have studied spin-wave propagation in a system with corrugation induced magnetic anisotropy. The corrugated magnetic film is created by focused electron beam-induced deposition of nonmagnetic ridges on a substrate and subsequent deposition of the magnetic material. Turned corrugated waveguides of different designs were prepared and we have measured spin-wave propagation through them by Brillouin light scattering microscopy. Micromagnetic simulations were also employed to provide further insight and to help us identify good experimental designs.

Interaction of stress and magnetic properties in patterned copper-nickel-copper thin films

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 135-137).In recent years, the epitaxial Cu/Ni/Cu thin film system has been extensively studied, due to its wide range of perpendicular magnetization. It has proved to be a model system to explore the interactions of strain, surface energies and magnetic properties. For that reason, is also an ideal system to explore the effects of patterning. It is expected that the miniaturization of patterned magnetic devices will be accompanied by a transition from polycrystalline to epitaxial films. This transition will require a detailed theoretical understanding of the interaction of strain and magnetic properties in patterned epitaxial magnetic thin films. The Cu/Ni/Cu film system is used in this work to explore a triaxial model for an orthorhombic symmetry of strain. By patterning the Cu/Ni into nanolines and measuring the resulting magnetic anisotropy, the validity of the model has been tested. It has been shown that upon patterning certain thicknesses of nickel into nanolines, the easy axis of magnetization shifts from out of the film plane to in-plane, transverse to the line direction, an observation at odds with the direction of magnetization predicted by shape considerations alone. This transition is explained by the dominant magnetoelastic energy for the Cu/Ni/Cu nanoline system.(cont.) The resulting anisotropy values are consistent with strain relief values predicted by finite element modeling. In addition, the low temperature properties of the Cu/Ni/Cu epitaxial film system have been explored. The variation of the overall magnetic anisotropy as a function of temperature is found to be proportional to the cube of the reduced magnetization. In addition, the easy axis of magnetization for certain thicknesses of nickel has been found to shift from in-plane to perpendicular with the reduction of temperature.by Elizabeth Friend.Ph.D

Epitaxial Growth and Intrinsic Magnetic Properties of Magnetic Thin Films on Semiconductor Materials

Spin electronics, or spintronics, is an emergent interdisciplinary area whereby the spin degree of freedom in electronic devices is employed. One of the most important topics of spintronics is to develop magnetic/semiconductor hybrid materials for the next generation spin devices such as Spin-FET. This dissertation investigates the magnetic properties of magnetic thin films deposited on semiconductor substrate. Fe and Ni films have been deposited onto GaAs substrate with different substrate treatment. Both single and poly crystalline samples were developed during the process, and the magnetic properties were compared to explore the differences. The origin of a uniaxial magnetic anisotropy (UMA) from the crystal symmetry of the bcc Fe, observed in Fe/GaAs (100) has been investigated. Another major work for this thesis is the Artemis TR-ARPES (time resolved – angular resolved photoemission spectroscopy) project in Rutherford Appleton Laboratory. Successful MBE growth was achieved for the first time during the Artemis TR-ARPES project, followed by static and time-resolved MOKE, and time-resolved photoemission measurements. Preliminary time-resolved photoemission spectroscopy measurements has been performed on the single crystal Fe samples, which is the world first result in term of the study of the time-dependent valence band structures using direct photoemission technique from a metallic material. The research finally extended to the CoFeB film on GaAs substrate. The discovery of uniaxial magnetic anisotropy of this amorphous film make it one of the hottest topic in research. XMCD measurements were conducted and the results went through a series of calculations gives an indication of the relation between magnetic moment to the anisotropy. TEM inspections offers a clear look at the interface of the samples

Spin currents and ferromagnetic resonance in magnetic thin films

2017 Summer.Includes bibliographical references.Spin currents represent a new and exciting phenomenon. There is both a wealth of new physics to be discovered and understood, and many appealing devices which may result from this area of research. To fully realize the potential of this discipline it is necessary to develop new methods for realizing spin currents and explore new materials which may be suitable for spin current applications. Spin currents are an inherently dynamic phenomenon involving the transfer of angular momentum within and between different thin films. In order to understand and optimize such devices the dynamics of magnetization must be determined. This dissertation reports on novel approaches for spin current generation utilizing the magnetic insulators yttrium iron garnet (YIG) and M-type barium hexagonal ferrite (BaM). First, the light-induced spin Seebeck effect is reported for the first time in YIG. Additionally, the first measurement of the spin Seebeck effect without an external magnetic field is demonstrated. To accomplish this the self-biased BaM thin films are utilized. Second, a new method for the generation of spin currents is presented: the photo-spin-voltaic effect. In this new phenomenon, a spin current may be generated by photons in a non-magnetic metal that is in close proximity to a magnetic insulator. On exposure to light, there occurs a light induced, spin-dependent excitation of electrons in a few platinum layers near the metal/magnetic insulator interface. This excitation gives rise to a pure spin current which flows in the metal. This new effect is explored in detail and extensive measurements are carried out to confirm the photonic origin of the photo-spin-voltaic effect and exclude competing effects. In addition to the spin current measurements, magnetization dynamics were probed in thin films using ferromagnetic resonance (FMR). In order to determine the optimal material configuration for magnetic recording write heads, FMR measurements were used to perform damping studies on a set of FeCo samples with different numbers of lamination layers. The use of lamination layers has the potential to tune the damping in such films, while leaving the other magnetic properties unchanged. Finally, the sensitivity of the vector network analyzer FMR technique was improved. The use of field modulation and lock-in detection, along with the background subtraction of a Mach-Zehnder microwave interferometer working as a notch filter, is able to increase the sensitivity and lower the background noise of this measurement technique. This improved system opens the possibility of probing previously difficult samples with extremely low signals

Fabrication and application of patterned magnetic media

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006."September 2006."Includes bibliographical references (leaves 66-70).In order to overcome the superparamagnetism in thin film magnetic recording media, a novel magnetic medium, called patterned medium, is studied here as a potential candidate for the future hard disk storage application. Within the patterned medium, one bit is stored in one magnetic unit, which has to be prepared "to-precision" along the track at uniform periodicity. A variety of magnetic recording media will be introduced and compared first. Detailed discussion will be focused on the potential techniques for patterned media fabrication. IP environment, market competition and business models will be given at the end.by Guhua Yao.M.Eng

DMI Interaction and Domain Evolution in Magnetic Heterostructures with Perpendicular Magnetic Anisotropy

My thesis is dedicated to the study of the magnetic interactions and magnetization reversal dynamics in ferromagnetic heterostructures with perpendicular magnetic anisotropy (PMA). Two related projects will be included: 1) investigating interfacial Dzyaloshinskii-Moriya interaction (DMI) in multilayer structures; 2) controlled stripe domain growth in PMA heterostructures. Magneto Optic Kerr Effect microscopy and magnetometry techniques along with vibrating sample magnetometry were used to investigate these phenomena. The CoPt bi-layer system is a well-known PMA material system exhibiting DMI. However, films with many CoPt bi-layers are known as having zero effective DMI due to its inversion symmetry. I focused my research on CoNiPt tri-layer heterostructures with broken inversion symmetry. In my project, the interfacial DMI as a function of the number of CoNiPt tri-layers in multilayered films was investigated and non-zero DMI in this constructed “bulk” magnetic materials were observed. For the project of stripe domain manipulation, the CoNi bi-layer system with PMA was studied. CoNi “bulk” multilayered materials with PMA allow for controlled direction of stripe domain growth. The formation of variable angle domain intersection segments is comprised of the stripe domains