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Epitaxial growth, structural characterization, and exchange bias of noncollinear antiferromagnetic Mn3Ir thin films

James M. Taylor, Edouard Lesne, Anastasios Markou, Fasil Kidane Dejene, Benedikt Ernst, Adel Kalache, Kumari Gaurav Rana, Neeraj Kumar, Peter Werner, Claudia Felser, and Stuart S. P. Parkin
Phys. Rev. Materials 3, 074409 – Published 30 July 2019
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  • INTRODUCTION
  • EXPERIMENTAL METHODS
  • FILM GROWTH AND STRUCTURAL…
  • EXCHANGE BIAS
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    Antiferromagnetic materials are of great interest for spintronics. Here we present a comprehensive study of the growth, structural characterization, and resulting magnetic properties of thin films of the noncollinear antiferromagnet Mn3Ir. Using epitaxial engineering on MgO (001) and Al2O3 (0001) single-crystal substrates, we control the growth of cubic γ-Mn3Ir in both (001) and (111) crystal orientations, and discuss the optimization of growth conditions to achieve high-quality crystal structures with low surface roughness. Exchange bias is studied in bilayers, with exchange bias fields as large as −29 mT (equivalent to a unidirectional anisotropy constant of 0.115ergcm−2 or 11.5nJcm−2) measured in Mn3Ir (111)/Permalloy heterostructures at room temperature. In addition, a distinct dependence of blocking temperature on in-plane crystallographic direction in Mn3Ir (001)/Permalloy bilayers is observed. These findings are discussed in the context of antiferromagnetic domain structures, and will inform progress towards chiral antiferromagnetic spintronic devices.

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    • Received 13 March 2019

    DOI:https://doi.org/10.1103/PhysRevMaterials.3.074409

    ©2019 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    AntiferromagnetismExchange biasMagnetismSpintronics
    1. Physical Systems
    AntiferromagnetsThin filmsTopological materials
    1. Techniques
    EpitaxyFilm depositionSputtering
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    James M. Taylor1,*, Edouard Lesne1, Anastasios Markou2, Fasil Kidane Dejene1, Benedikt Ernst2, Adel Kalache2, Kumari Gaurav Rana1, Neeraj Kumar1, Peter Werner1, Claudia Felser2, and Stuart S. P. Parkin1,†

    • 1Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany
    • 2Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany

    • *james.taylor@mpi-halle.mpg.de
    • †stuart.parkin@mpi-halle.mpg.de

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    Vol. 3, Iss. 7 — July 2019

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    Images

    • Figure 1
      Figure 1

      (a) Measured x-ray reflectivity data from a 10-nm Mn3Ir (001) film, with fit to determine layer thicknesses. (b) XRD 2θ-θ scans measured for 10-nm Mn3Ir (001) films grown at different temperatures (inset shows rms roughness measured by AFM for each of these samples).

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    • Figure 2
      Figure 2

      (a) Dependence of grain size and OP lattice parameter on growth temperature. AFM topography maps of 3-nm Mn3Ir films with (b) (001) and (c) (111) orientation.

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    • Figure 3
      Figure 3

      (a) Crystal and magnetic structure of L12 ordered Mn3Ir with [001] axis directed out-of-plane, demonstrating cube-on-cube epitaxy with a (001)-oriented MgO substrate. (b) XRD χ-ϕ pole figure measuring ⟨111⟩ peaks in a 10-nm Mn3Ir film with (001) orientation, aligned such that the [100] and [010] axes of the MgO substrate are directed along ϕ=0∘ and ϕ=90∘, respectively.

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    • Figure 4
      Figure 4

      (a) XRD off-specular scan map measuring (111) reflections from a 10-nm Mn3Ir film with (001) orientation and the MgO (001) substrate upon which it is grown. (b) Plane-view TEM image of a 3-nm Mn3Ir (001) thin film, prepared using ion-beam backside thinning.

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    • Figure 5
      Figure 5

      (a) XRD 2θ-θ patterns measured for 10-nm Mn3Ir (111) films grown using different buffer layers (scans are offset for clarity). (b) XRD ω rocking curve for a 10-nm Mn3Ir (111) film grown on a TaN buffer layer, with fit to determine FWHM.

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    • Figure 6
      Figure 6

      (a) Crystal and magnetic structure of (111) planes in L12 ordered Mn3Ir, of (111) planes in TaN and of (0001) planes in Al2O3, showing the epitaxial relation between them as viewed along the OP axis. (b) XRD χ-ϕ pole figure measuring ⟨002⟩ peaks in a 10-nm Mn3Ir film with (111) orientation and a 5-nm TaN (111) buffer layer, aligned such that the [112¯0] axis of the Al2O3 substrate is directed along ϕ=0∘.

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    • Figure 7
      Figure 7

      (a) Cross-sectional HAADF-STEM image of a 10-nm Mn3Ir (111) film, grown on an Al2O3 substrate with (0001) orientation using a 5-nm (111) textured TaN buffer layer, viewed along the [11¯0] zone axis. (b) Diffractogram (fast Fourier transform) of the above experimental image. The epitaxial correlation between the Mn3Ir and TaN lattices is demonstrated by the corresponding indexed reflections.

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    • Figure 8
      Figure 8

      (a) Magnetization hysteresis loops at 300 K for an as-deposited 10-nm Mn3Ir (001)/Py bilayer, and for the same sample after 1-T IP field annealing at 550 K (with μ0HFA∥[100]), with IP measurement field directed parallel and perpendicular to μ0HFA. (b) Magnetization hysteresis loops at 300 K for a 10-nm Mn3Ir (111)/Py bilayer after 1-T IP field annealing at different temperatures (with μ0HFA∥[1¯1¯2]) (inset shows variation of μ0HEB with annealing temperature).

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    • Figure 9
      Figure 9

      (a) μ0HEB measured at different temperatures after 1-T IP field cooling from 400 K for a 3-nm Mn3Ir (001)/Py bilayer, with μ0HFC∥[100] and [110] crystal axes (inset shows normalized magnetization hysteresis loops recorded at 5 K after different field-cooling protocols with μ0HFC∥[100]). (b) μ0HEB measured at different temperatures after 1-T IP field cooling from 400 K for a 3-nm Mn3Ir (111)/Py bilayer, with μ0HFC∥[1¯1¯2], [01¯1], and [12¯1] crystal axes (inset shows normalized magnetization hysteresis loops recorded at 5 K after different field-cooling protocols with μ0HFC∥[1¯1¯2]).

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    • Figure 10
      Figure 10

      (a) Exchange-bias training effect showing variation of μ0HEB and μ0HC with successive measurement field cycles at different temperatures after 1-T IP field cooling from 300 K for a 3-nm Mn3Ir (001)/Py bilayer (with μ0HFC∥[100]). (b) Blocking temperature distribution showing μ0HEB and μ0HC measured at 5 K after 1-T IP FC from different starting temperatures for a 3-nm Mn3Ir (111)/Py bilayer (with μ0HFC∥[1¯1¯2]).

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