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Title: Magnetic Tunnel Junctions Based on CrO 2/SnO 2 Epitaxial Bilayers

Abstract

Magnetic tunnel junctions (MTJs) were fabricated using thin films of the half-metallic ferromagnet CrO2, employing semiconducting SnO2 tunnel barriers. Heteroepitaxial CrO2/SnO2 bilayers were grown on (100)-TiO2 substrates via chemical vapor deposition under atmospheric conditions. X-ray diffraction and transmission electron microscopy were used to confirm heteroepitaxy. A polycrystalline cobalt film forms the top magnetic electrode, yielding CrO2(001)/SnO2(001)/Co structures after patterning. Tunneling magnetoresistances (TMR) up to +14% at 5 K were observed. The sign of the TMR reverses for barrier thicknesses < 1nm, attributed to tunneling being dominated by Co-3d states at low thicknesses, and Co-4s states at larger thicknesses.

Authors:
 [1];  [1];  [1];  [2];  [2]
  1. University of Alabama, Tuscaloosa
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003563
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 89; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL VAPOR DEPOSITION; COBALT; SUBSTRATES; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY; TUNNELING; X-RAY DIFFRACTION

Citation Formats

Miao, G. X., LeClair, P., Gupta, A., Varela del Arco, Maria, and Pennycook, Stephen J. Magnetic Tunnel Junctions Based on CrO2/SnO2 Epitaxial Bilayers. United States: N. p., 2006. Web. doi:10.1063/1.2216109.
Miao, G. X., LeClair, P., Gupta, A., Varela del Arco, Maria, & Pennycook, Stephen J. Magnetic Tunnel Junctions Based on CrO2/SnO2 Epitaxial Bilayers. United States. doi:10.1063/1.2216109.
Miao, G. X., LeClair, P., Gupta, A., Varela del Arco, Maria, and Pennycook, Stephen J. Sun . "Magnetic Tunnel Junctions Based on CrO2/SnO2 Epitaxial Bilayers". United States. doi:10.1063/1.2216109.
@article{osti_1003563,
title = {Magnetic Tunnel Junctions Based on CrO2/SnO2 Epitaxial Bilayers},
author = {Miao, G. X. and LeClair, P. and Gupta, A. and Varela del Arco, Maria and Pennycook, Stephen J},
abstractNote = {Magnetic tunnel junctions (MTJs) were fabricated using thin films of the half-metallic ferromagnet CrO2, employing semiconducting SnO2 tunnel barriers. Heteroepitaxial CrO2/SnO2 bilayers were grown on (100)-TiO2 substrates via chemical vapor deposition under atmospheric conditions. X-ray diffraction and transmission electron microscopy were used to confirm heteroepitaxy. A polycrystalline cobalt film forms the top magnetic electrode, yielding CrO2(001)/SnO2(001)/Co structures after patterning. Tunneling magnetoresistances (TMR) up to +14% at 5 K were observed. The sign of the TMR reverses for barrier thicknesses < 1nm, attributed to tunneling being dominated by Co-3d states at low thicknesses, and Co-4s states at larger thicknesses.},
doi = {10.1063/1.2216109},
journal = {Applied Physics Letters},
number = 2,
volume = 89,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • This paper reports a systematic investigation on the structural and magnetic properties of Fe{sub 2}Cr{sub 1−x}Co{sub x}Si Heusler alloys with various compositions of x by co-sputtering Fe{sub 2}CrSi and Fe{sub 2}CoSi targets and their applications in magnetic tunnel junctions (MTJs). Fe{sub 2}Cr{sub 1−x}Co{sub x}Si films of high crystalline quality have been epitaxially grown on MgO substrate using Cr as a buffer layer. The L2{sub 1} phase can be obtained at x = 0.3 and 0.5, while B2 phase for the rest compositions. A tunnel magnetoresistance (TMR) ratio of 19.3% at room temperature is achieved for MTJs using Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si asmore » the bottom electrode with 350 °C post-annealing. This suggests that the Fermi level in Fe{sub 2}Cr{sub 1−x}Co{sub x}Si has been successfully tuned close to the center of band gap of minority spin with x = 0.7 and therefore better thermal stability and higher spin polarization are achieved in Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si. The post-annealing effect for MTJs is also studied in details. The removal of the oxidized Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si at the interface with MgO barrier is found to be the key to improve the TMR ratio. When the thickness of the inserted Mg layer increases from 0.3 to 0.4 nm, the TMR ratio is greatly enhanced from 19.3% to 28%.« less
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  • The ability of the full Heusler alloy Co{sub 1.5}Fe{sub 1.5}Ge(001) (CFG) to be a Half-Metallic Magnetic (HMM) material is investigated. Epitaxial CFG(001) layers were grown by molecular beam epitaxy. The results obtained using electron diffraction, X-ray diffraction, and X-ray magnetic circular dichroism are consistent with the full Heusler structure. The pseudo-gap in the minority spin density of state typical in HMM is examined using spin-resolved photoemission. Interestingly, the spin polarization found to be negative at E{sub F} in equimolar CoFe(001) is observed to shift to positive values when inserting Ge in CoFe. However, no pseudo-gap is found at the Fermimore » level, even if moderate magnetization and low Gilbert damping are observed as expected in HMM materials. Magneto-transport properties in MgO-based magnetic tunnel junctions using CFG electrodes are investigated via spin and symmetry resolved photoemission.« less
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