Positive exchange bias in epitaxial permalloy/MgO integrated with Si (1 0 0) |
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| Affiliation: | 1. Materials Science Division, Army Research Office, Research Triangle Park, NC 27709, USA;2. Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA;3. Center for Advanced Materials and Smart Structures, North Carolina A&T University, Greensboro, NC 27411, USA;4. Department of Physics, University of Nebraska, Lincoln, NE 68588, USA;1. Division of Functional Materials, Central Iron and Steel Research Institute, Beijing 100081, China;2. Key Laboratory of National Education Ministry for Electromagnetic Processing of Materials, Northeastern University, Shenyang 110819, China;3. School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China;1. PetroChina Dalian Lubricating Oil R&D Institute, Dalian 116023, China;2. State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China;1. Université de Tours, CNRS, GREMAN, UMR 7347, 37200 Tours, France;2. Université de Strasbourg, CNRS, IPCMS, UMR 7504, 67000 Strasbourg, France |
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| Abstract: | In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni82.5Fe17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0). |
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| Keywords: | Positive exchange bias Permalloy islands Epitaxial integration Pulsed laser deposition Domain matching epitaxy |
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