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Title: Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions

Abstract

Growth and magnetic characterization of thin films of Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and Co{sub 2}MnSi full-Heusler compounds are investigated. Thin films were deposited by magnetron sputtering at room temperature directly onto oxidized Si wafers. These Heusler films are magnetically very soft and ferromagnetic with Curie temperatures well above room temperature. Polycrystalline Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al Heusler films combined with MgO barriers and CoFe counter electrodes are structured to magnetic tunnel junctions and yield almost 50% magnetoresistance at room temperature. The magnetoresistance shows a strong bias dependence with the maximum occurring at a voltage drop well above 1 V. This special feature is accompanied by only a moderate temperature dependence of the tunnel magnetoresistance.

Authors:
; ; ;  [1]
  1. Institute of Solid State Research, Electronic Properties (IFF-9) and cni-Center of Nanoelectronic Systems for Information Technology, Research Center Juelich GmbH, D-52425 Juelich (Germany)
Publication Date:
OSTI Identifier:
20982863
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 9; Conference: 10. joint MMM/INTERMAG conference, Baltimore, MD (United States), 7-11 Jan 2007; Other Information: DOI: 10.1063/1.2711070; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHROMIUM ALLOYS; COBALT ALLOYS; CRYSTAL GROWTH; CURIE POINT; DEPOSITION; ELECTRODES; HEUSLER ALLOYS; IRON ALLOYS; MAGNESIUM OXIDES; MAGNETORESISTANCE; POLYCRYSTALS; SILICON ALLOYS; SPUTTERING; SUPERCONDUCTING JUNCTIONS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; THIN FILMS; TUNNEL EFFECT; VOLTAGE DROP

Citation Formats

Rata, A. D., Braak, H., Buergler, D. E., and Schneider, C. M. Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions. United States: N. p., 2007. Web. doi:10.1063/1.2711070.
Rata, A. D., Braak, H., Buergler, D. E., & Schneider, C. M. Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions. United States. doi:10.1063/1.2711070.
Rata, A. D., Braak, H., Buergler, D. E., and Schneider, C. M. Tue . "Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions". United States. doi:10.1063/1.2711070.
@article{osti_20982863,
title = {Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions},
author = {Rata, A. D. and Braak, H. and Buergler, D. E. and Schneider, C. M.},
abstractNote = {Growth and magnetic characterization of thin films of Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and Co{sub 2}MnSi full-Heusler compounds are investigated. Thin films were deposited by magnetron sputtering at room temperature directly onto oxidized Si wafers. These Heusler films are magnetically very soft and ferromagnetic with Curie temperatures well above room temperature. Polycrystalline Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al Heusler films combined with MgO barriers and CoFe counter electrodes are structured to magnetic tunnel junctions and yield almost 50% magnetoresistance at room temperature. The magnetoresistance shows a strong bias dependence with the maximum occurring at a voltage drop well above 1 V. This special feature is accompanied by only a moderate temperature dependence of the tunnel magnetoresistance.},
doi = {10.1063/1.2711070},
journal = {Journal of Applied Physics},
number = 9,
volume = 101,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • The effect of annealing on the changes in the inelastic tunneling contributions in tunneling conductance of ion beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions (MTJs) is investigated. The inelastic contributions are evaluated using hopping conduction model of Glazman and Matveev in the temperature range of 25–300 K. The hopping through number of series of localized states present in the barrier due to structural defects increases from 9 (in as deposited MTJ) to 18 after annealing (at 200 °C/1 h); although no changes in the interface roughness of CoFe-MgO and MgO-NiFe interfaces are observed as revealed by the x-ray reflectance studies on planar MTJs. Themore » bias dependence of tunneling magnetoresistance (TMR) at 25 K is found to get improved after annealing as revealed by the value V{sub 1/2} (the bias value at which the TMR reaches to half of its value at nearly zero bias); which is 78 mV (in MTJ annealed at 200 °C/1 h) 2.5 times the value of 33 mV (in as deposited MTJ). At 25 K the inelastic tunneling spectra revealed the presence of zero bias anomaly and magnon excitations in the range of 10–15 mV. While the barrier height exhibited a strong temperature dependence with nearly 100% increase from the value at 300 K to 25 K, the temperature dependence of TMR becomes steep after annealing.« less
  • Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co{sub 2}FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes. The present finding suggests that Co{sub 2}FeAl may be one of the most promising candidates for future spintronics devices applications.
  • To obtain magnetic tunnel junctions (MTJs) composed of non-equilibrium alloy, Co{sub 2}FeSn films were prepared by atomically controlled alternate deposition at various substrate temperatures. X-ray diffraction patterns and Moessbauer spectra clarify that Co{sub 2}FeSn films in the Heusler alloy phase can be realized by growing at a substrate temperature of 250 deg. C or below. Phase separation into cubic CoSn, hexagonal CoSn and cubic CoFe phases occurs in films grown at substrate temperatures 300 deg. C or greater. Fe/MgO/Co{sub 2}FeSn MTJs were prepared with the Co{sub 2}FeSn layer grown at various substrate temperatures. The MTJs with the ferromagnetic Co{sub 2}FeSnmore » layer grown at a substrate temperature of 250 deg. C showed tunnel magnetoresistance ratios of 72.2% and 43.5% at 2 K and 300 K, respectively.« less
  • The interface magnetism between Co{sub 2}FeGe Heusler alloy layers and MgO layers was investigated using {sup 57}Fe Mössbauer spectroscopy. Interface-sensitive samples, where the {sup 57}Fe isotope was used only for the interfacial atomic layer of the Co{sub 2}FeGe layer on the MgO layer, were prepared using atomically controlled alternate deposition. The {sup 57}Fe Mössbauer spectra of the interface-sensitive samples at room temperature were found similar to those of the bulk-sensitive Co{sub 2}FeGe films in which the {sup 57}Fe isotope was distributed throughout the films. On the other hand, the tunnel magnetoresistance effect of magnetic tunnel junctions with Co{sub 2}FeGe layersmore » as the ferromagnetic electrodes showed strong reduction at room temperature. These results indicate that the strong temperature dependence of the tunneling magnetoresistance of magnetic tunnel junctions using Heusler alloy electrodes cannot be attributed simply to the reduction of the magnetization at the interfaces between the Heusler alloy and insulator layers.« less
  • Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be asmore » high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.« less