Antiferromagnetic Material

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Hiroshi Naganuma - One of the best experts on this subject based on the ideXlab platform.

  • field free spin hall effect driven magnetization switching in pd co irmn exchange coupling system
    Applied Physics Letters, 2016
    Co-Authors: W J Kong, Yang Ji, Xuan Zhang, Hao Wu, Quande Zhang, Z H Yuan, Tian Yu, Kenji Fukuda, Hiroshi Naganuma
    Abstract:

    All electrical manipulation of magnetization is crucial and of great important for spintronics devices for the sake of high speed, reliable operation, and low power consumption. Recently, widespread interests have been aroused to manipulate perpendicular magnetization of a ferromagnetic layer using spin-orbit torque (SOT) without field. We report that a commonly used Antiferromagnetic Material IrMn can be a promising candidate as a functional layer to realize field-free magnetization switching driven by SOT in which IrMn is employed to act as both the source of effective exchange bias field and SOT source. The critical switching current density within our study is Jc = 2.2 × 107 A/cm2, which is the same magnitude as similar Materials such as PtMn. A series of measurements based on anomalous Hall effect was systematically implemented to determine the magnetization switching mechanism. This study offers a possible route for IrMn application in similar structures.

Michael A Seigler - One of the best experts on this subject based on the ideXlab platform.

  • Current-in-plane giant magnetoresistance sensor using a thin Cu spacer and dual nano-oxide layers with a DR greater than 20 Ohms/sq
    IEEE Transactions on Magnetics, 2007
    Co-Authors: Michael A Seigler
    Abstract:

    The magnetoresistance (MR) of the current-in-plane spin-valve, which is currently utilized as the readback sensor in the majority of hard disk drives, has reached a maximum MR of DR/Rmin. ∼ 20% and DRsheet ∼ 4 Ω/sq. A new sensor film stack will be introduced here that utilizes a trilayer (CoFe\Cu\CoFe), where the Cu interlayer is very thin (∼10 Å) to enhance the MR and where the Cu thickness is chosen such that the ferromagnetic Neel coupling and the Antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between the CoFe layers partially cancel one another, to maximize the sensitivity. By changing the Cu interlayer thickness, the overall interlayer coupling was adjusted from about -0.05 erg/cm² to -0.4 erg/cm² while keeping the MR large. Nano-oxide layers (NOLs) are also incorporated below and above the trilayer sensor to enhance the MR. An example of this sensor is NiFeCr 20 Å/CoFeO 10 Å/CoFe 15 Å/Cu 10.5 Å/CoFe 15 Å/AIO 30 Å and will be referred to as CIP-3L. With the combination of the thin Cu spacer, the NOLs and minimal additional layers to shunt the current around the trilayer sensor (no Antiferromagnetic Material and no pinned layers), as deposited sheet films with an MR of DR/R > 25 % and DR/sq. > 20 Ω/sq. were achieved. This paper shows the optimization of the sensor stack, such as film thicknesses, NOL Material, and oxidation process, the adjustability of the interlayer exchange coupling between the CoFe layers and also shows the repeatability of the sensor deposition. [ABSTRACT FROM AUTHOR]

  • Current-in-Plane Giant Magnetoresistance Sensor Using a Thin Cu Spacer and Dual Nano-Oxide Layers With a ${\rm DR}$ Greater Than $20$ Ohms/sq.
    IEEE Transactions on Magnetics, 2007
    Co-Authors: Michael A Seigler
    Abstract:

    The magnetoresistance (MR) of the current-in-plane spin-valve, which is currently utilized as the readback sensor in the majority of hard disk drives, has reached a maximum MR of DR/Rmin.~20% and DRsheet~4 Omega/sq. A new sensor film stack will be introduced here that utilizes a trilayer (CoFe\Cu\CoFe) where the Cu interlayer is very thin (~10 Aring) to enhance the MR and where the Cu thickness is chosen such that the ferromagnetic Neel coupling and the Antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between the CoFe layers partially cancel one another, to maximize the sensitivity. By changing the Cu interlayer thickness, the overall interlayer coupling was adjusted from about -0.05 erg/cm2 to -0.4 erg/cm2 while keeping the MR large. Nano-oxide layers (NOLs) are also incorporated below and above the trilayer sensor to enhance the MR. An example of this sensor is NiFeCr 20 Aring/CoFeO 10 Aring/CoFe 15 Aring/Cu 10.5 Aring/CoFe 15 Aring/AlO 30 Aring and will be referred to as CIP-3L. With the combination of the thin Cu spacer, the NOLs and minimal additional layers to shunt the current around the trilayer sensor (no Antiferromagnetic Material and no pinned layers), as deposited sheet films with an MR of DR/R >25% and DR/sq. >20 Omega/sq. were achieved. This paper shows the optimization of the sensor stack, such as film thicknesses, NOL Material, and oxidation process, the adjustability of the interlayer exchange coupling between the CoFe layers and also shows the repeatability of the sensor deposition

A. Schuhl - One of the best experts on this subject based on the ideXlab platform.

Andrea Migliorini - One of the best experts on this subject based on the ideXlab platform.

  • spontaneous exchange bias formation driven by a structural phase transition in the Antiferromagnetic Material
    Nature Materials, 2018
    Co-Authors: Andrea Migliorini
    Abstract:

    Un gran numero de dispositivos magneticos en la electronica moderna se basan en el exchange bias, una interaccion magnetica que acopla un Material ferromagnetico y uno Antiferromagnetico, dando origen a un desplazamiento unidireccional del ciclo de histeresis ferromagnetico en una cantidad llamada exchange bias field. Establecer y optimizar el exchange bias implica un tratamiento termico en presencia de un campo magnetico externo, que permite controlar el grado de orden magnetico en el Material Antiferromagnetico. En esta tesis, demostramos un proceso alternativo para la generacion del exchange bias. Nuestro estudio se centra en uno de los sistemas mas comunes para aplicaciones tecnologicas basado en el exchange bias, el FeCo ferromagnetico acoplado al IrMn Antiferromagnetico en forma de peliculas delgadas depositada por magnetron sputtering. Hemos encontrado las condiciones de deposicion que dejan la capa IrMn en una fase amorfa/nanocristalina metaestable. El estado desordenado del IrMn previene el establecimiento del exchange bias en la capa de FeCo adyacente, la cual muestra un ciclo de histeresis centrado y con baja coercitividad tipico de las peliculas delgadas ferromagneticas blandas. Durante los dias sucesivos a la deposicion, una transicion de fase estructural se desarrolla espontaneamente a temperatura ambiente en la capa de IrMn y se expande siguiendo un proceso de nucleacion y crecimiento bidimensional. A medida que la transicion de fase se propaga, el exchange bias se forma progresivamente en el FeCo segun la direccion de su imanacion remanente. La caracterizacion estructural de las bicapas de IrMn/FeCo revela que el IrMn, inicialmente amorfo/nanocristalino, experimenta una cristalizacion espontanea que conduce a una fase quimicamente desordenada de tipo γ, altamente cristalina. Una vez completada la transicion de fase, la capa de IrMn contiene granos cristalinos muy grandes, del orden de unos cientos de nanometros, con una gran densidad de defectos estructurales que se extienden a traves de su espesor. Las imagenes tomadas por microscopia electronica de transmision indican que el origen de estos defectos puede residir en la naturaleza policristalina de la capa de FeCo adyacente. La caracterizacion magnetica de las muestras cristalizadas revela un exchange bias moderadamente fuerte con buena estabilidad a temperatura ambiente. Las medidas muestran tambien unas respuestas magneticas y termicas inesperadas que no se pueden explicar con el modelo granular del exchange bias, generalmente utilizado para Materiales policristalinos. Con el fin de justificar como cambian las propiedades de las muestras cristalizadas durante el recocido a varias temperaturas, analizamos los resultados a la luz de un modelo de fuerte fijacion de paredes Antiferromagnetica, que indica que los defectos estructurales en la capa de IrMn juegan un papel importante tanto en la estabilidad como en la resistencia del exchange bias. Ademas, proponemos un posible mecanismo para el establecimiento inicial del exchange bias, lo que explicaria el aumento progresivo del exchange bias field durante su formacion espontanea, a medida que la fase cristalina se propaga. Finalmente, abordamos la interesante posibilidad de controlar la direccion del exchange bias, simplemente cambiando la imanacion de la capa de FeCo a medida que se propaga la transicion de fase. Esto permite el modelado microscopico de la direccion del exchange bias, lo que generalmente no es posible a menos que la muestra se trate localmente con laser o radiacion ionica. El estudio de este mecanismo para establecer y modelar el exchange bias en los sistemas de IrMn/FeCo puede contribuir a aclarar aspectos fundamentales de este fenomeno, asi como a nuevos desarrollos en el campo de la espintronica. ----------ABSTRACT---------- Most magnetic devices in advanced electronics rely on the exchange bias effect, a magnetic interaction that couples a ferromagnetic and an Antiferromagnetic Material, resulting in a unidirectional displacement of the ferromagnetic hysteresis loop by an amount called the “exchange bias field”. Setting and optimizing the exchange bias involves a thermal treatment in presence of an external magnetic field, which allows to control the degree of magnetic order in the Antiferromagnetic Material. In this thesis we demonstrate an alternative process for the generation of exchange bias. Our study focuses on one of the most common systems for technological applications based on exchange bias, which is the ferromagnetic FeCo coupled to the Antiferromagnetic IrMn in the form of a multilayered thin film deposited by magnetron sputtering. We have found the deposition conditions which leave the IrMn layer in a metastable amorphous/nanocrystalline phase. The disordered state of the IrMn prevents the setting of the exchange bias in the adjacent FeCo layer, which shows a centered hysteresis loop with low coercivity, typical of soft ferromagnetic thin films. During the days after deposition, a structural phase transition in the IrMn layer develops spontaneously at room temperature and spreads according to a two-dimensional nucleation and growth process. As the phase transition propagates, the FeCo gets progressively exchange-biased according to the direction of its remanent magnetization. The structural characterization of the IrMn/FeCo bilayers reveals that the as-deposited amorphous/nanocrystalline IrMn undergoes a spontaneous crystallization which leads to a highly crystalline, chemically-disordered γ-phase. Once the phase transition is completed, the IrMn layer consists of very large single-crystal grains, of the order of few hundred nanometers, with a large density of structural defects which extend through its thickness. The images taken by transmission electron microscopy indicate that the origin of these defects may lie in the polycrystalline nature of the adjacent FeCo layer. The magnetic characterization of the crystallized samples shows a moderately strong exchange bias with good stability at room temperature. It also reveals some unexpected magnetic and thermal responses which cannot be explained with the granular model for the exchange bias, generally used for polycrystalline Materials. In order to justify the properties of the crystallized samples upon field annealing, we analyze the results in light of a strong Antiferromagnetic domain walls pinning model, which indicates that the structural defects in the IrMn layer may play an important role in both the stability and the strength of the exchange bias. Furthermore, we propose a possible mechanism for the initial setting of the exchange bias, which would explain the progressive increase of the exchange bias field during its spontaneous formation, as the crystalline phase propagates. Finally, we report the interesting possibility of controlling the direction of the exchange bias, simply by switching the magnetization of the FeCo layer as the phase transition propagates. This allows microscopic patterning of the direction of the exchange bias, which is generally not possible unless the sample is locally treated with laser or ion radiation. The study of this mechanism for establishing and tailoring the exchange bias in IrMn/FeCo systems can contribute toward the clarification of fundamental aspects of this phenomenon, as well as toward further developments in the field of spintronics.

Leslie M Schoop - One of the best experts on this subject based on the ideXlab platform.

  • soft chemical synthesis of hxcrs2 an Antiferromagnetic Material with alternating amorphous and crystalline layers
    Journal of the American Chemical Society, 2019
    Co-Authors: Xiaoyu Song, Guangming Cheng, Daniel Weber, Florian Pielnhofer, Sebastian Klemenz, Kai A Filsinger, Craig B Arnold, Leslie M Schoop
    Abstract:

    We report a new HxCrS2-based crystalline/amorphous layered Material synthesized by soft chemical methods. We study the structural nature and composition of this Material with atomic resolution scanning transmission electron microscopy (STEM), revealing a complex structure consisting of alternating layers of amorphous and crystalline lamellae. Furthermore, the magnetic properties show evidence for increased magnetic frustration compared to the parent compound NaCrS2. Finally, we show that this Material can be exfoliated, thus providing a facile synthesis method for chromium-sulfide-based ultrathin layers. The Material reported herein can not only be a source of new thin TMD-related sheets for potential application in catalysis but also be of interest for realizing new 2D magnetic Materials.