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Title: Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode

Abstract

Spinel MgAl{sub 2}O{sub 4} thin films were deposited on MgO single-crystal substrates and epitaxial Fe (or Fe{sub 4}N) thin films by RF-sputtering from a ceramic target. Epitaxial relationship was confirmed by X-ray diffraction analysis between the crystalline spinel MgAl{sub 2}O{sub 4} films and the respective substrate and underlayers, while no diffraction peak was observed from the films deposited on amorphous substrates. Spin-valve type magnetic tunnel junctions (MTJs) with a stacking structure of Fe [Fe{sub 4}N]/MgAl{sub 2}O{sub 4}/CoFeB/Ru/Fe/MnIr exhibited normal [inverse] tunnel magnetoresistance (TMR) effect, reflecting the sign of spin polarization of Fe [Fe{sub 4}N]. The maximum magnitude of the TMR ratio obtained for the Fe-based and Fe{sub 4}N-based MTJs was 67% and 18%, respectively. The resistance area product values of the MTJs were significantly larger than the reported values for the MTJs with a post-oxidized spinel MgAl{sub 2}O{sub 4} barrier.

Authors:
; ;  [1]
  1. Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, 6-6-05 Aobayama, Sendai 980-8579 (Japan)
Publication Date:
OSTI Identifier:
22410090
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 17; 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; ALUMINATES; CERAMICS; EPITAXY; INTERFACES; IRON NITRIDES; MAGNESIUM OXIDES; MAGNETORESISTANCE; MONOCRYSTALS; RADIOWAVE RADIATION; SPIN ORIENTATION; SPINELS; SPUTTERING; SUBSTRATES; THIN FILMS; TUNNEL EFFECT; X-RAY DIFFRACTION

Citation Formats

Tsunoda, Masakiyo, Chiba, Ryoichi, and Kabara, Kazuki. Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode. United States: N. p., 2015. Web. doi:10.1063/1.4906762.
Tsunoda, Masakiyo, Chiba, Ryoichi, & Kabara, Kazuki. Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode. United States. doi:10.1063/1.4906762.
Tsunoda, Masakiyo, Chiba, Ryoichi, and Kabara, Kazuki. Thu . "Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode". United States. doi:10.1063/1.4906762.
@article{osti_22410090,
title = {Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode},
author = {Tsunoda, Masakiyo and Chiba, Ryoichi and Kabara, Kazuki},
abstractNote = {Spinel MgAl{sub 2}O{sub 4} thin films were deposited on MgO single-crystal substrates and epitaxial Fe (or Fe{sub 4}N) thin films by RF-sputtering from a ceramic target. Epitaxial relationship was confirmed by X-ray diffraction analysis between the crystalline spinel MgAl{sub 2}O{sub 4} films and the respective substrate and underlayers, while no diffraction peak was observed from the films deposited on amorphous substrates. Spin-valve type magnetic tunnel junctions (MTJs) with a stacking structure of Fe [Fe{sub 4}N]/MgAl{sub 2}O{sub 4}/CoFeB/Ru/Fe/MnIr exhibited normal [inverse] tunnel magnetoresistance (TMR) effect, reflecting the sign of spin polarization of Fe [Fe{sub 4}N]. The maximum magnitude of the TMR ratio obtained for the Fe-based and Fe{sub 4}N-based MTJs was 67% and 18%, respectively. The resistance area product values of the MTJs were significantly larger than the reported values for the MTJs with a post-oxidized spinel MgAl{sub 2}O{sub 4} barrier.},
doi = {10.1063/1.4906762},
journal = {Journal of Applied Physics},
number = 17,
volume = 117,
place = {United States},
year = {Thu May 07 00:00:00 EDT 2015},
month = {Thu May 07 00:00:00 EDT 2015}
}
  • Magnetic properties of Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) thin films sandwiched between Ta and MgAl{sub 2}O{sub 4} layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl{sub 2}O{sub 4} structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy K{sub i} = 1.22 erg/cm{sup 2}, which further increases to 1.30 erg/cm{sup 2} after annealing, while MgAl{sub 2}O{sub 4}/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a coremore » structure of CoFeB/MgAl{sub 2}O{sub 4}/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.« less
  • We developed a fabrication process of an epitaxial MgAl{sub 2}O{sub 4} barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl{sub 2}O{sub 4} spinel sintered target. Annealing the sputter-deposited MgAl{sub 2}O{sub 4} layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl{sub 2}O{sub 4}/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative methodmore » for the realization of high performance MTJs with a spinel-based tunnel barrier.« less
  • The first microporous solids incorporating two octahedrally coordinated transition elements, the phosphates (TMA)[sub 2](NH[sub 4])[sub 2][Fe[sub 2]Mo[sub 12]O[sub 30](H[sub 2]PO[sub 4])[sub 6](HOP[sub 4])[sub 2]][center dot]11H[sub 2]O (1) and (TMA)[sub 2]Na[sub 4][Fe[sub 3]Mo[sub 12]O[sub 30](H[sub x]PO[sub 4])[sub 8]][center dot]16H[sub 2]O (2) (TMA = (CH[sub 3])[sub 4]N[sup +]), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction and water absorption isotherms. Phosphate 1 is prepared in 94% yield from Na[sub 2]MoO[sub 4], Mo, FeCl[sub 3], (NH[sub 4])[sub 2]HPO[sub 4], (TMA)OH, H[sub 3]PO[sub 4], and H[sub 2]O in a mole ratio of 5:1:1:2:7:16:150 at 200[degrees]C for 64 h, while 2 is synthesizedmore » in 62% yield by the reaction of Na[sub 2]MoO[sub 4], Mo, FeCl[sub 3], (TMA)OH, H[sub 3]PO[sub 4] and H[sub 2]O in a mole ratio of 5:1:1:8:18:250 at 200[degrees]C for 3 days. Orange crystals of 1 are rhombohedral. Both structures are based on Fe[Mo[sub 6]O[sub 15](H[sub x]PO[sub 4])[sub 2]] units which are connected via their phosphate groups to additional Fe[sup 3+] ions to give three-dimensional frameworks. Both compounds display structures that can be rationalized on the basis of regions of hydrophobic and hydrophilic interactions. The interconnected voids and channels in the ferric molybdenum phosphate frameworks are filled with a mixture of charged-compensating cations and water of solvation. Reversible water absorption isotherms indicate that both compounds are microporous with internal void volumes of about 15 and 25 vol % for 1 and 2, respectively. 23 refs., 10 figs., 3 tabs.« less
  • Fe{sub 3}O{sub 4} is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe{sub 3}O{sub 4} electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe{sub 3}O{sub 4} films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe{sub 3}O{sub 4}(110) films exhibited in-plane uniaxial magnetic anisotropy. Withmore » respect to the squareness of hysteresis, Fe{sub 3}O{sub 4} (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe{sub 3}O{sub 4}(110) electrodes and obtained a TMR effect of −12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe{sub 3}O{sub 4} predicted from band calculations.« less
  • Zn{sub 1-x}Fe{sub x}O thin films were grown on Al{sub 2}O{sub 3}(0001) substrates by radio-frequency magnetron sputtering. The alloys show wurtzite crystal structure up to x=0.24 with reduced c-axis lattice constant compared to that of pure ZnO. Fe 2p core-level photoemission measurements reveal the evidence for the coexistence of the Fe{sup 3+} and Fe{sup 2+} ions substituting the tetrahedral the Zn{sup 2+} sites. The optical properties of the samples were measured by the spectroscopic ellipsometry at room temperature in the 1.5-5 eV photon energy region. With increasing x, the optical band-gap (E{sub 0}) absorption edge is found to shift slightly tomore » lower energies (70 meV for x=0.24) than that of the pure ZnO. Below the E{sub 0} edge, optical absorption structures are observed at about 1.7, 2.4, and 2.8 eV. These structures are interpreted as due to the d-d transitions from the {sup 6}A{sub 1} ground state to the excited states, {sup 4}T{sub 1} (1.7 eV), {sup 4}T{sub 2} (2.4 eV), and {sup 4}E and {sup 4}A{sub 1} (2.8 eV), of the crystal-field-split 3d{sup 5} multiplets of the tetrahedral Fe{sup 3+} ion.« less