Unveiling the role of Co-O-Mg bond in magnetic anisotropy of $\mathrm{Pt}/\mathrm{Co}/\mathrm{MgO}$ using atomically controlled deposition and in situ electrical measurement

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of $Pt / Co / MgO$ using atomically controlled deposition and in situ electrical measurement

Yumeng Yang, Jiaren Yuan, Long Qi, Ying Wang, Yanjun Xu, Xiaowei Wang, Yuanping Feng, Baoxi Xu, Lei Shen, and Yihong Wu

Phys. Rev. B 95, 094417 – Published 13 March 2017

Abstract

Despite the crucial role of interfacial perpendicular magnetic anisotropy in a Co(Fe)/MgO-based magnetic tunnel junction, the underlying mechanism is still being debated. Here, we report an anatomical study of the oxygen and Mg effect on $Pt / Co$ bilayers through repeated in situ anomalous Hall effect measurements, controlled oxygen exposure, and Mg deposition in an ultrahigh vacuum system. We found that chemisorbed oxygen not only quenches the effective magnetic moment of the Co surface layer, but also softens its magnetic anisotropy. However, a subsequent Mg dusting on the oxygen preexposed $Pt / Co$ surface can recover the magnetic anisotropy. The ab initio calculations on the exchange splitting and orbital hybridization near the Fermi level give a clear physical explanation of the experimental observations. Our results suggest that the Co(Fe)-O- $M$ bond plays a more important role than the widely perceived Co(Fe)-O bond does in realizing interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.

Received 13 December 2016
Revised 20 February 2017

DOI:https://doi.org/10.1103/PhysRevB.95.094417

Physics Subject Headings (PhySH)

Magnetic anisotropy Spintronics

Ab initio calculations

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Yumeng Yang¹, Jiaren Yuan^2,3, Long Qi¹, Ying Wang¹, Yanjun Xu^1,4, Xiaowei Wang¹, Yuanping Feng³, Baoxi Xu⁴, Lei Shen^5,*, and Yihong Wu^1,†

¹Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583, Singapore
²College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, People's Republic of China
³Department of Physics, Centre for Advanced Two-dimensional Materials, National University of Singapore, Singapore 117542, Singapore
⁴Data Storage Institute, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, 08-01 Innovis, Singapore 138634, Singapore
⁵Department of Mechanical Engineering, Engineering Science Programme, Faculty of Engineering, National University of Singapore, Singapore 117575, Singapore

^*shenlei@nus.edu.sg
^†elewuyh@nus.edu.sg

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 95, Iss. 9 — 1 March 2017

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a)–(c) AHE loops for $Ta (1.5) / Pt (3) / Co (t_{Co})$ with $t_{Co} = 0.2 - 1.9 nm$ . Note that the curves in (a)–(c) are vertically shifted for clarify.
Reuse & Permissions
Figure 2
(a) Schematic of the coordinate system adopted for deriving Eq. (1); (b) plot of $- H M_{s} / (2 cos θ)$ against $2 {sin}^{2} θ$ from AHE loops of the $t_{Co} = 1.9$ -nm (circle) and $t_{Co} = 1.8$ -nm (triangle) samples and the linear fitting (solid line); (c) summary of the estimated $K_{eff}$ values with $t_{Co} = 1.6 - 1.9 nm$ ; (d) and (e) fitting of AHE loops for $Ta (1.5) / Pt (3) / Co (t_{Co})$ with $t_{Co} = 1.7 - 1.9 nm$ using the normal distribution; (f) fitting of the AHE loops with $t_{Co} = 1.2 - 1.6 nm$ without consideration of the normal distribution (open square: experimental data; solid line: fitting results). Note that the curves in (d)–(f) are vertically shifted for clarify.
Reuse & Permissions
Figure 3
(a) and (b) AHE loops for $Ta (1.5) / Pt (3) / Co (0.6)$ with different oxygen preexposure doses; (c) AHE loops for $Ta (1.5) / Pt (3) / Co (1.9)$ with different oxygen preexposure doses. The topmost curves in (a) and (c) are obtained after annealing. Note that the curves in (a)–(c) are shifted vertically for clarity.
Reuse & Permissions
Figure 4
(a) Comparison of the AHE loops for pristine samples with $t_{Co} = 0.4$ and 1.8 nm and O exposed samples with $t_{Co} = 0.6$ and $t_{Co} = 1.9 nm$ ; (b) oxygen dose dependence of the $M_{r} / M_{s}$ ratio for the $t_{Co} = 0.6$ -nm sample; (c) oxygen dose dependence of the $M_{r} / M_{s}$ ratio for the $t_{Co} = 1.9$ -nm sample; (d) comparison of the AHE loops for $Ta (1.5) / Pt (3) / Co (0.8)$ at pristine, preexposed, Mg dusting, and reexposed states; (e) comparison of the AHE loops for $Ta (1.5) / Pt (3) / Co (0.6)$ at pristine, Mg dusting, and reexposed states. Note that the $M_{r} / M_{s}$ ratio of the $t_{Co} = 0.4$ , 1.7, 1.8-nm pristine samples is added in (b) and (c) as a reference, and the curves in (a), (d), and (e) are shifted vertically for clarity.
Reuse & Permissions
Figure 5
Schematics for optimized structures used in ab initio calculations of (a) oxygen-exposed $Pt / Co / O$ ; (b) Mg dusted preexposed $Pt / Co / O / Mg$ . Note that Pt, Co, O, and Mg are represented by blue, pink, red, and green balls, respectively. The charge-density difference (top view) plotted using an isovalue of $0.012 e Å^{- 3}$ for (c) $Pt / Co / O$ and (d) $Pt / Co / O / Mg$ . The red (blue) region indicates an accumulation (depletion) of electrons. Majority spin (positive) and minority spin (negative) PDOS on the $p$ orbitals of O and $d$ orbitals of Co in (e) and (f) for $Pt / Co / O$ and in (g) and (h) for $Pt / Co / O / Mg$ , respectively. The zero of energy is set at the Fermi level, and a dashed line is added as a guidance to the eye. The inset in (h) is PDOS on the $d$ orbitals of Co in $Pt / Co$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of $Pt / Co / MgO$ using atomically controlled deposition and in situ electrical measurement

Yumeng Yang, Jiaren Yuan, Long Qi, Ying Wang, Yanjun Xu, Xiaowei Wang, Yuanping Feng, Baoxi Xu, Lei Shen, and Yihong Wu

Phys. Rev. B 95, 094417 – Published 13 March 2017

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in situ electrical measurement

Yumeng Yang, Jiaren Yuan, Long Qi, Ying Wang, Yanjun Xu, Xiaowei Wang, Yuanping Feng, Baoxi Xu, Lei Shen, and Yihong Wu

Phys. Rev. B 95, 094417 – Published 13 March 2017

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Unveiling the role of Co-O-Mg bond in magnetic anisotropy of $Pt / Co / MgO$ using atomically controlled deposition and in situ electrical measurement