Spin Hall magnetoresistance in a canted ferrimagnet

Kathrin Ganzhorn, Joseph Barker, Richard Schlitz, Benjamin A. Piot, Katharina Ollefs, Francois Guillou, Fabrice Wilhelm, Andrei Rogalev, Matthias Opel, Matthias Althammer, Stephan Geprägs, Hans Huebl, Rudolf Gross, Gerrit E. W. Bauer, and Sebastian T. B. Goennenwein

Phys. Rev. B 94, 094401 – Published 1 September 2016

Abstract

We study the spin Hall magnetoresistance effect in ferrimagnet/normal metal bilayers, comparing the response in collinear and canted magnetic phases. In the collinear magnetic phase, in which the sublattice magnetic moments are all aligned along the same axis, we observe the conventional spin Hall magnetoresistance. In contrast, in the canted phase, the magnetoresistance changes sign. Using atomistic spin simulations and x-ray absorption experiments, we can understand these observations in terms of the magnetic field and temperature dependent orientation of magnetic moments on different magnetic sublattices. This enables a magnetotransport based investigation of noncollinear magnetic textures.

Received 24 May 2016

DOI:https://doi.org/10.1103/PhysRevB.94.094401

Physics Subject Headings (PhySH)

Cellular bilayers Spin Hall magnetoresistance

Ferrimagnets Magnetic insulators Noncollinear magnets

Hall bar Molecular dynamics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Kathrin Ganzhorn^1,2, Joseph Barker³, Richard Schlitz^1,2, Benjamin A. Piot⁴, Katharina Ollefs^5,6, Francois Guillou⁵, Fabrice Wilhelm⁵, Andrei Rogalev⁵, Matthias Opel¹, Matthias Althammer^1,2, Stephan Geprägs¹, Hans Huebl^1,2,7, Rudolf Gross^1,2,7, Gerrit E. W. Bauer^3,8,9, and Sebastian T. B. Goennenwein^1,2,7,*

¹Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany
²Physik-Department, Technische Universität München, 85748 Garching, Germany
³Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan
⁴Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS-UGA-UPS-INSA-EMFL, F-38042 Grenoble, France
⁵European Synchrotron Radiation Facility (ESRF), 38043 Grenoble Cedex 9, France
⁶Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, D-47057 Duisburg, Germany
⁷Nanosystems Initiative Munich (NIM), 80799 München, Germany
⁸Kavli Institute of NanoScience, Delft University of Technology, 2628 CJ Delft, The Netherlands
⁹WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

^*Present address: Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany; goennenwein@wmi.badw.de

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Vol. 94, Iss. 9 — 1 September 2016

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Images

Figure 1
Spin Hall magnetoresistance (SMR) response of a magnetic insulator/metal bilayer. (a) When the spin current $J_{s}$ in the metal is absorbed by the magnet, the resistivity $ρ$ of the metal is large. (b) When $J_{s}$ is reflected at the interface, $ρ$ is small owing to the inverse spin Hall effect. (c) and (d) In a collinear magnet, the spin transfer across the interface and thus $ρ$ is largest for $μ ⊥ s$ (c), while spin transfer and $ρ$ are minimal for $μ | | s$ (d). (e) and (f) In a noncollinear magnet in which, e.g., the orientation of the $μ_{FeA}$ moments dominate the spin transfer across the interface, large viz. small $ρ$ arises for the corresponding orientations of $μ_{FeA}$ with respect to $s$ . An externally applied magnetic field $H$ (larger than the weak anisotropy but smaller than the interspin exchange fields) determines the orientation of $μ_{net}$ . Comparing (c)–(f), the $H$ orientations for maximum viz. minimum $ρ$ in the canted viz. collinear magnet are interchanged—the SMR inverts sign.
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Figure 2
Magnetic phase diagram of GdIG calculated by atomistic spin simulations (see text). The main panel depicts the orientation of the FeA sublattice moment orientation $ξ_{FeA}$ encoded in color, the inset shows $ξ_{Gd}$ of the Gd sublattice moments. Due to the strong antiferromagnetic exchange coupling, the FeD sublattice moments are always antiparallel to the FeA ones. The black lines indicate the temperature dependence of the upper $(μ_{0} H_{c 2})$ and lower $(μ_{0} H_{c 1})$ critical fields which delimit the antiparallel, parallel, and spin canting phase [23, 24]. The orientation of the sublattice moments in each phase are represented by arrows.
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Figure 3
(a) Normalized XANES recorded at the Fe $K$ edge in the InYGdIG/Pt sample at 50 K and 17 T. The pre-edge marked by a black arrow arises mainly from the tetrahedrally ordered FeD moments. The blue curve represents the corresponding XMCD signal, which is dominated by the signal at the pre-edge. (b) XMCD amplitude, i.e., the projection of the FeD moments onto the external field axis, measured as a function of field strength at various temperatures around $T_{comp}$ .
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Figure 4
Measured evolution of the magnetoresistance in YIG/Pt (a)–(c) and InYGdIG/Pt (d)–(f). The data were recorded at $T = 10$ , 85, and 300 K as a function of the angle $α_{H}$ between the current direction $J_{c}$ and the orientation of the external, in-plane magnetic field $μ_{0} H = 7$ T. The SMR in InYGdIG/Pt inverts sign around the magnetization compensation temperature $T_{comp} \approx 85$ K (e), but the extrema stay at the same $α_{H}$ for all temperatures.
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Figure 5
SMR amplitude Eq. (3) as a function of temperature and magnetic field, as measured for InYGdIG (main figure), and calculated for GdIG (inset) only taking the iron moments into account. In the blue regions the SMR is positive, i.e., has the same sign and $α_{H}$ dependence as for a single-sublattice ferromagnet [cf. Fig. 1]. The red regions indicate negative SMR [as in Fig. 4]. No data has been taken in the regions shaded in gray.
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