Effect of Seed Layer on Room Temperature Tunnel Magnetoresistance of MgO Barriers Formed by Radical Oxidation in IrMn-Based Magnetic Tunnel Junctions

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<jats:p>NiFe-seeded magnetic tunnel junctions (MTJs) of IrMn/CoFe/MgO/CoFeB were successfully formed by radically oxidizing a thin Mg layer. Room temperature (RT) tunnel magnetoresistance (TMR) of up to 211±10% was obtained and found to be strongly dependent on the thickness of the NiFe seed layer. High resolution transmission microscopy (HRTEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and magneto-optic Kerr effect (MOKE) analyses performed on NiFe/IrMn bilayer systems revealed that the IrMn(111)-fcc texture, grain size, surface roughness (rms), and exchange-biasing field (<jats:italic>H</jats:italic><jats:sub>ex</jats:sub>) were strongly affected by the thickness of the NiFe seed layer. A critical NiFe thickness (<jats:italic>t</jats:italic><jats:sub>c</jats:sub>≈12 Å) was found: For<jats:italic>t</jats:italic><jats:sub>NiFe</jats:sub>≤<jats:italic>t</jats:italic><jats:sub>c</jats:sub>, the IrMn showed a very poor (111)-fcc texture with reduced grain size, very smooth surface, and reduced<jats:italic>H</jats:italic><jats:sub>ex</jats:sub>. For<jats:italic>t</jats:italic><jats:sub>NiFe</jats:sub>><jats:italic>t</jats:italic><jats:sub>c</jats:sub>, the IrMn showed a complete opposite behavior: much enhanced (111)-fcc texture with larger grain size, rougher surface, and larger<jats:italic>H</jats:italic><jats:sub>ex</jats:sub>. For MTJ-based IrMn systems, a striking behavior is reported: larger TMRs and lower tunnel junction resistance (<jats:italic>RA</jats:italic>) products are obtained for<jats:italic>t</jats:italic><jats:sub>NiFe</jats:sub>≤<jats:italic>t</jats:italic><jats:sub>c</jats:sub>while lower TMRs and larger<jats:italic>RA</jats:italic>s are obtained for<jats:italic>t</jats:italic><jats:sub>NiFe</jats:sub>><jats:italic>t</jats:italic><jats:sub>c</jats:sub>.</jats:p>

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