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Competing magnetic interactions in exchange-bias-modulated films

Christine Hamann, Jeffrey McCord, Ludwig Schultz, Boris P. Toperverg, Katharina Theis-Bröhl, Maximilian Wolff, Rainer Kaltofen, and Ingolf Mönch
Phys. Rev. B 81, 024420 – Published 22 January 2010
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  • INTRODUCTION
  • EXPERIMENTAL
  • RESULTS
  • CONCLUSIONS
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    The magnetization reversal in stripelike exchange-bias-patterned Ni81Fe19/IrMn thin films was investigated by complementary inductive and high-resolution magneto-optical magnetometry, magneto-optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange-bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange-bias direction. Due to the interaction of interfacial coupling, exchange, and magnetostatic energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micropatterned exchange-bias films.

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    • Received 29 October 2009

    DOI:https://doi.org/10.1103/PhysRevB.81.024420

    ©2010 American Physical Society

    Authors & Affiliations

    Christine Hamann, Jeffrey McCord, and Ludwig Schultz

    • Institute for Metallic Materials, IFW Dresden, Postfach 270116, D-01171 Dresden, Germany

    Boris P. Toperverg*

    • Department of Physics and Astronomy, Institute for Solid State Physics, Ruhr-University Bochum, D-44780 Bochum, Germany

    Katharina Theis-Bröhl

    • University of Applied Sciences Bremerhaven, An der Karlstadt 8, D-27568 Bremerhaven, Germany

    Maximilian Wolff

    • Department of Physics, Uppsala University, P.O. Box 530, 751 21 Uppsala, Sweden

    Rainer Kaltofen and Ingolf Mönch

    • Institute for Integrative Nanosciences, IFW Dresden, Postfach 270116, D-01171 Dresden, Germany

    • *Also at Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188300, Russia; Institute Laue-Langevin, Grenoble, France.

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    Vol. 81, Iss. 2 — 1 January 2010

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    Images

    • Figure 1
      Figure 1
      (Color online) Schematics of the thin-film geometry with Dst being the stripe period. The magnetic and structural properties modulated over the stripe structure are shown.Reuse & Permissions
    • Figure 2
      Figure 2
      Scattering geometry for polarized neutron experiments.Reuse & Permissions
    • Figure 3
      Figure 3
      (Color online) Magnetic hysteresis loop of (a) NiFe(20 nm)/IrMn-IrMnO/Ta-IrMnO exchange-bias-patterned film with Dst=4 μm. The symbols represent the magnetic field for the PNR measurements (Fig. 4). Corresponding longitudinal Kerr images along the magnetization loop are depicted in (b)–(e). The external magnetic field values are indicated. The total magnetization direction for antiparallel stripe alignment in (c)-(d) is sketched as bold (yellow/dotted) arrow.Reuse & Permissions
    • Figure 4
      Figure 4
      (Color online) PNR specular reflectivity data (symbols) of NiFe(20 nm)/IrMn-IrMnO/Ta-IrMnO with Dst=4 μm and according fits (lines). The external magnetic field is aligned along the stripe axis and opposite to the unidirectional anisotropy. The magnetic field values and positions along the magnetization loop marked with the circle, square, triangle, and star correspond to those in Fig. 3.Reuse & Permissions
    • Figure 5
      Figure 5
      (Color online) Sketch of the alignment of mean total magnetization Mtot of NiFe(20 nm)/IrMn-IrMnO/Ta-IrMnO with Dst=4 μm derived from PNR fits (cf. Fig. 4). The different stripe properties are marked by different colors with the exchange-biased stripes in hatched red. The free NiFe stripes are labeled by dark gray bars. The applied field and direction of the unidirectional anisotropy Kud of the exchange-biased stripes are indicated.Reuse & Permissions
    • Figure 6
      Figure 6
      (Color online) Experimental (left column) and simulated (right column) polarized neutron-scattering intensity maps of NiFe(20 nm)/IrMn-IrMnO/Ta-IrMnO, Dst=4 μm. The intensities of R+ and R− are plotted as function of the incident and scattering angle αi and αf, respectively. The intensity is plotted in logarithmic scale.Reuse & Permissions
    • Figure 7
      Figure 7
      (Color online) Magnetization loops in longitudinal sensitivity in the left column (a)–(c) with the indicated magnetic field at the step and representative Kerr image. The bold (yellow/dotted) arrow indicates the total magnetization direction. The according experimental specular reflectivity measurements (symbols) and fits to the data (lines) are displayed in the right column (d)–(f). In the top row the data for the structures with NiFe of tF=20 nm and below the results for tF=30 nm are displayed. The magnetic field values and stripe periods of 4 and 12 μm are indicated. Note the different scales for the data of the two different ferromagnetic thicknesses tF of 20 and 30 nm.Reuse & Permissions
    • Figure 8
      Figure 8
      (Color online) Direction of the net total magnetization Mtot and opening angle Δγ at the partial antiparallel state calculated from the fit to the specular PNR data in Figs. 7d, 7e, 7f. With decreasing tF at constant stripe period the opening angle increases. Likewise, at constant tF=30 nm, with increasing stripe period, i.e., reduced F stripe interface volume Vif, the angle increases. The corresponding stripe-magnetization directions are marked by different colors with the EB stripes in red (pointing down) and the free F (NiFe) fraction in dark gray (pointing up) (cf. Fig. 5).Reuse & Permissions
    • Figure 9
      Figure 9
      (Color online) Longitudinal (∥) and transversal (⊥) magneto-optical magnetization loops of NiFe(20 nm)/IrMn-IrMnO/Ta-IrMnO the stripe period Dst=4 μm. The mean Kerr signal averaged over several stripes (F/AF-F) is shown in (a). Local measurements for the F and exchange-biased (AF-F) stripes are plotted in (b) and (c). The symbols represent the experimental data whereas the lines are introduced as guide to the eye.Reuse & Permissions
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