Giant Anomalous Hall Conductivity at the $\mathrm{Pt}/\mathrm{Cr}$2O3 Interface

Giant Anomalous Hall Conductivity at the $Pt / Cr$ ₂O₃ Interface

Takahiro Moriyama, Yu Shiratsuchi, Tatsuya Iino, Hikaru Aono, Motohiro Suzuki, Tetsuya Nakamura, Yoshinori Kotani, Ryoichi Nakatani, Kohji Nakamura, and Teruo Ono

Phys. Rev. Applied 13, 034052 – Published 20 March 2020

Abstract

The interface between a magnetic material and a heavy metal that has a large spin-orbit interaction is at the root of various spin-related phenomena. In this paper, we address the peculiar spin-dependent transport at a $Pt / {Cr}_{2} O_{3}$ interface by exploring the origin of the nonlinear anomalous Hall effect (AHE) in $Pt / {Cr}_{2} O_{3}$ bilayers. X-ray magnetic circular dichroism (XMCD) measurements show no appreciable magnetic moment at the interface originating from $Cr$ 3d and $Pt$ 5d orbitals, which could be associated with the AHE response. A possible interfacial magnetic moment M at the $Pt / {Cr}_{2} O_{3}$ interface, assumed from the detection limit of the XMCD measurements, yields an anomalous Hall conductivity ( $σ AHE$ ) per unit net magnetic moment (M), − $σ_{AHE}$ /M, of 0.57 $V^{- 1}$ , which is extraordinary large compared with that for general magnetic materials. Together with first-principles calculations, the results suggest the possibility of an intrinsic AHE in the $Pt / {Cr}_{2} O_{3}$ interface that does not rely on the net magnetic moment.

Received 29 August 2019
Revised 26 January 2020
Accepted 3 March 2020

DOI:https://doi.org/10.1103/PhysRevApplied.13.034052

Physics Subject Headings (PhySH)

Anomalous Hall effect Spin-orbit coupling Spintronics Surface & interfacial phenomena Topological Hall effect

Antiferromagnets Chiral magnets Magnetic multilayers

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Takahiro Moriyama ^1,*,‡, Yu Shiratsuchi ^2,†,‡, Tatsuya Iino¹, Hikaru Aono², Motohiro Suzuki³, Tetsuya Nakamura³, Yoshinori Kotani³, Ryoichi Nakatani², Kohji Nakamura⁴, and Teruo Ono¹

¹Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
²Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
³Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo 679-5198, Japan
⁴Department of Physics Engineering, Mie University, Tsu, Mie 514-8507, Japan

^*mtaka@scl.kyoto-u.ac.jp
^†shiratsuchi@mat.eng.osaka-u.ac.jp
^‡These authors contributed equally to this work.

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Vol. 13, Iss. 3 — March 2020

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Figure 1
RHEED patterns of (a) ${Cr}_{2} O_{3}$ surface, with a corresponding key diagram, and (b) 1-nm-thick $Pt$ and (c) 2-nm-thick $Pt$ layers on ${Cr}_{2} O_{3}$ . The electron azimuth is [ $11 \bar{2} 0$ ] of the α- ${Al}_{2} O_{3} (0001)$ substrate. (d) Key diagram for the ${Cr}_{2} O_{3}$ RHEED pattern.
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Figure 2
(a) ΔR_xx and (b) R_xy as a function of the external field for $Pt$ (1 nm)/ ${Cr}_{2} O_{3}$ (20 nm), with definition of ΔR_xy. The insets of (a) show an optical-microscope image of the fabricated Hall-cross pattern with a measurement diagram, and ρ_xx as a function of t_Pt. Anomalous Hall conductivity σ_AHE as a function of temperature (c) and as a function of 1/t_Pt (d). Δρ_xy/ρ_xx as a function of temperature (e) and as a function of t_Pt (f). The inset of (f) shows G_i, estimated from curve fitting with Eq. (1), as a function of temperature.
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Figure 3
(a) XAS and XMCD spectra at the $Pt$ L₃ edge for the $Pt$ (1 nm)/ ${Cr}_{2} O_{3}$ (20 nm) film. The measurement temperature is 350 K. The applied out-of-plane magnetic field during the measurements is 1.3 T. (b) XMCD spectrum at the $Pt$ L₃ edge after MEFC, measured using $Pt$ (1 nm)/ ${Cr}_{2} O_{3}$ (200 nm) prepared on a 0.5-wt % $Nb$ -doped ${Sr Ti O}_{3} (111)$ substrate. The magnetic field and voltage during the MEFC are +1.3 T and +1.2 V, respectively. The measurement temperature is 28 K. The x-ray absorption intensity and the XMCD intensity are normalized by the XAS edge jump. (c) XAS and XMCD spectra at the $Cr$ L_2,3 edges for the $Pt$ (1 nm)/ ${Cr}_{2} O_{3}$ (20 nm) film. The measurement temperature is 300 K. The applied magnetic field during the measurements is 1.9 T in the direction perpendicular to the film. (d) Magnetic field dependence of the XMCD intensity. The difference between the XMCD signals measured at the photon energies labeled A and B in (c) is taken and plotted as a function of the external field. The XMCD intensity in (d) is normalized by the total absorption intensity, (µ₊ − µ₋)/(µ₊ + µ₋).
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Figure 4
(a),(b) Top and side views of calculated interface structure of $Pt / {Cr}_{2} O_{3}$ . (c) Relation between σ′_AHE and the spin magnetic moments of $Pt$ at the interface in $Pt / {Cr}_{2} O_{3}$ , where the red and blue solid circles represent results for the fully optimized interface structure and when the interlayer distance between the $Pt$ and ${Cr}_{2} O_{3}$ films is changed by 1 Å [ $Pt$ (/+1 Å)/ ${Cr}_{2} O_{3}$ ]. The open circles show the AHE as a function of the spin magnetic moment in a freestanding $Pt$ film consisting of two atomic (111) layers. (d) Band structure and (e) variation of σ′_AHE along the high-symmetry k directions. The inset of (d) shows two constant-energy contours around the K-point in the two-dimensional Brillouin zone, at 7 meV above (yellow) and 3 meV below (green) E_F, where arrows indicate the in-plane components of the spin magnetic moments.
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Physical Review Applied

Giant Anomalous Hall Conductivity at the Pt/Cr2O3 Interface

Takahiro Moriyama, Yu Shiratsuchi, Tatsuya Iino, Hikaru Aono, Motohiro Suzuki, Tetsuya Nakamura, Yoshinori Kotani, Ryoichi Nakatani, Kohji Nakamura, and Teruo Ono

Phys. Rev. Applied 13, 034052 – Published 20 March 2020

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Giant Anomalous Hall Conductivity at the $Pt / Cr$ ₂O₃ Interface