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Title: Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

Abstract

Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.

Authors:
; ; ; ; ; ;  [1]; ;  [2]; ; ;  [3];  [4];  [5]
  1. State Key Laboratory of Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)
  2. Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom)
  3. Department of Materials Engineering and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel)
  4. Department of Physics and Quantum Theory Project, University of Florida, Gainesville, Florida 32611 (United States)
  5. (United States)
Publication Date:
OSTI Identifier:
22413156
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; COMPARATIVE EVALUATIONS; DIFFUSION BARRIERS; ELECTRODES; INTERFACES; INTERMETALLIC COMPOUNDS; IRON; MAGNESIUM OXIDES; MAGNETORESISTANCE; MOLECULAR BEAM EPITAXY; PHOTOELECTRON SPECTROSCOPY; PLATINUM; SPIN; TEMPERATURE DEPENDENCE; TRANSMISSION ELECTRON MICROSCOPY; TUNNEL EFFECT

Citation Formats

Yang, G., Li, D. L., Wang, S. G., E-mail: Sgwang@iphy.ac.cn, Ma, Q. L., Liang, S. H., Wei, H. X., Han, X. F., Hesjedal, T., Ward, R. C. C., Kohn, A., Elkayam, A., Tal, N., Zhang, X.-G., and Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions. United States: N. p., 2015. Web. doi:10.1063/1.4913265.
Yang, G., Li, D. L., Wang, S. G., E-mail: Sgwang@iphy.ac.cn, Ma, Q. L., Liang, S. H., Wei, H. X., Han, X. F., Hesjedal, T., Ward, R. C. C., Kohn, A., Elkayam, A., Tal, N., Zhang, X.-G., & Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions. United States. doi:10.1063/1.4913265.
Yang, G., Li, D. L., Wang, S. G., E-mail: Sgwang@iphy.ac.cn, Ma, Q. L., Liang, S. H., Wei, H. X., Han, X. F., Hesjedal, T., Ward, R. C. C., Kohn, A., Elkayam, A., Tal, N., Zhang, X.-G., and Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493. Sat . "Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions". United States. doi:10.1063/1.4913265.
@article{osti_22413156,
title = {Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions},
author = {Yang, G. and Li, D. L. and Wang, S. G., E-mail: Sgwang@iphy.ac.cn and Ma, Q. L. and Liang, S. H. and Wei, H. X. and Han, X. F. and Hesjedal, T. and Ward, R. C. C. and Kohn, A. and Elkayam, A. and Tal, N. and Zhang, X.-G. and Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6493},
abstractNote = {Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.},
doi = {10.1063/1.4913265},
journal = {Journal of Applied Physics},
number = 8,
volume = 117,
place = {United States},
year = {Sat Feb 28 00:00:00 EST 2015},
month = {Sat Feb 28 00:00:00 EST 2015}
}
  • The plasma treatment with O{sub 2}/Ar mixture was applied to reduce the surface roughness of the L1{sub 0}-FePt electrode in perpendicular magnetic tunnel junctions. The surface roughness (R{sub rms}) of the L1{sub 0}-FePt layer was decreased from 1.2 nm at the as-deposited state to 0.52 nm after the plasma treatment with the ratio of O{sub 2} to Ar equal to 0.5. The low surface roughness accompanying the formation of an oxide layer led to magnetic decoupling between free and reference layers after the plasma treatment on the surface of FePt layer. The existence of the oxide layer was confirmed bymore » using transmission electron microscopy and x-ray photoelectron spectroscopy. The interfacial Pt-oxide layer plays a significant role in the magnetic decoupling.« less
  • Magnetic tunnel junctions (MTJs) using L1{sub 0}-ordered CoPt electrodes with perpendicular magnetic anisotropy were fabricated. Full-epitaxial CoPt/MgO/CoPt-MTJs were prepared onto single crystal MgO-(001) substrate by sputtering method. X-ray diffraction analyses revealed that both bottom and top CoPt electrodes were epitaxially grown with (001)-orientation. The L1{sub 0}-chemical order parameter of 0.82 was obtained for the bottom CoPt electrode deposited at substrate temperature of 600 deg. C. The transport measurements with applying magnetic field perpendicular to the film plane showed a tunnel magnetoresistance ratio of 6% at room temperature and 13% at 10 K.
  • Low-voltage spin-dependent tunneling spectroscopy of an epitaxial Fe/MgO/Fe magnetic tunnel junction is measured and compared to first-principles calculation of the tunneling conductance. The measured dynamic conductance ($dI/dV$) in the parallel configuration shows distinct asymmetric features as a function of the bias voltage $V$. The peaks are independent of barrier thickness, magnetic field, and temperature. From the first-principles calculation, we identify the positive and negative bias spectra corresponding to different types of Fe/MgO interfaces. Tunneling spectroscopy thus can be used as a powerful tool for interface characterization.
  • Perpendicular anisotropy L1{sub 0}-FePt/Ag/[Co/Pd]{sub 30} pseudo spin valves (PSVs) with ultra-thin L1{sub 0}-FePt alloy free layer possessing high anisotropy and thermal stability have been fabricated and studied. The thickness of the L1{sub 0}-FePt layer was varied between 2 and 4 nm. The PSV became increasingly decoupled with reduced L1{sub 0}-FePt thickness due to the larger difference between the coercivity of the L1{sub 0}-FePt and [Co/Pd]{sub 30} films. The PSV with an ultra-thin L1{sub 0}-FePt free layer of 2 nm displayed a high K{sub u} of 2.21 × 10{sup 7} ergs/cm{sup 3}, high thermal stability of 84 and a largest giant magnetoresistance of 0.54%.
  • We investigated the thickness and composition dependence of perpendicular magnetic anisotropy (PMA) in L1{sub 0} Fe{sub 1-x}Pt{sub x} (x = 0.4, 0.5, and 0.55) films. The FePt films with different thicknesses of 35 and 70 A were grown at the substrate temperature T{sub s} = 300 deg. C by molecular beam epitaxy coevaporation technique. A (001)-oriented epitaxial L1{sub 0} FePt film was grown on the thin (001)-oriented fcc Pt layer, while a poorly crystallized FePt film was formed on the (111)-textured Pt layer. Our results showed that, at a fixed thickness of 70 A, the PMA of FePt alloy filmsmore » is enhanced as Pt content increases from 40% to 55%.« less