Towards a multi-level antiferromagnetic bit cell

  • Authors

    Kriegner,1 K. Výborný,2 K. Olejníık,2 H. Reichlová,2 V. Novák,2 X. Marti,2 J. Gazquez,3 V. Saidl,1 P. Nemec,1 V.V. Volobuev,4,5 G. Springholz,4 V. Holý,1 T. Jungwirth2,6

  • Publication

    Multiple-stable anisotropic magnetoresistance memory in antiferromagnetic MnTe
    Nature Communications, 7, 11623, 2016
  • Figure

    (a) Cross-sectional HAADF image xis resolving the individual atomic columns of Mn (magenta) and Te (green). The inset shows the atomic positions including the Mn magnetic moments in the ordered antiferromagnetic state.

    (b,c) Transverse (red) and longitudinal (blue) AMR measurements. Arrow in b indicates the initial angle and the direction of rotation.

    (d) Transverse AMR measured after cooling in a magnetic field (BFC=2T) applied at an angle 𝜑B,FC and with the field kept on. The dashed line is a guide to the eye.

    (e) Zero-field transverse AMR obtained after field-cooling (BFC=2 T) down to 5 K then removing the field and taking zero-field resistance measurements at 200 K. The grey line is a ∼ sin2𝜑B,FC least squares fit which fails to describe the details of the angular variation in the experimental data. On the other hand, the red line shows the least square fit of the multi-domain model calculations, which accurately reproduce the angular variation of the experimental data.

In contrast to most commercial memories which rely on the bi-stability of ordered spin states, in this work it has been shown that multiple stable resistance states can be realized in antiferromagnets, which may lead to higher memory capacity. The multiple stability of the memory is a result of different magnetic domain distributions. The zero-magnetic moment intrinsic to antiferromagnets lead to considerable robustness against strong magnetic field perturbations.

It has been used 𝛼-MnTe thin films grown epitaxially on single crystalline InP substrates with (111) oriented surface by molecular beam epitaxy. Below the Néel temperature, which is 310 K in bulk 𝛼-MnTe, the magnetic structure consists of ferromagnetically ordered Mn-planes which are antiferromagnetically stacked along the c-direction. It has been demonstrated a smoothly varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic angular dependence on the writing magnetic field angle, analogous to ferromagnets. The continuously varying AMR provides means for the electrical read-out of multiple-stable antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by changing the writing field direction. The multiple stability in our memory is ascribed to different distributions of domains with the Ne ́el vector aligned along one of the three magnetic easy axes. These multiple-stable states are not erased by even strong magnetic-field perturbations.

1 Charles University in Prague, Czech Republic
2 Institute of Physics, Academy of Science of the Czech Republic, Czech Republic
3 Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
4 Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Austria
5 National Technical University, Kharkiv Polytechnic Institute, Ukraine
6 School of Physics and Astronomy, University of Nottingham, UK

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