Lattice Softening in Metastable bcc Co x Mn 100 − x
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· 2021
· Open Access
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· DOI: https://doi.org/10.1103/physrevapplied.16.054052
· OA: W3215423171
In spintronics, one of the long-standing questions is why the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mrow><a:mi>Mg</a:mi><a:mi mathvariant="normal">O</a:mi></a:mrow></a:math>-based magnetic tunnel junction (MTJ) is almost the only option for achieving a large tunneling magnetoresistance (TMR) ratio at room temperature, although this is not as large as the theoretical prediction. This study focuses on the development of an almost strain-free MTJ using metastable bcc <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><e:msub><e:mi>Co</e:mi><e:mi>x</e:mi></e:msub><e:msub><e:mi>Mn</e:mi><e:mrow><e:mn>100</e:mn><e:mstyle displaystyle="false" scriptlevel="0"><e:mtext>−</e:mtext></e:mstyle><e:mi>x</e:mi></e:mrow></e:msub></e:math> (<j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><j:mi>Co</j:mi><j:mtext>−</j:mtext><j:mi>Mn</j:mi></j:math>) ferromagnetic films. We investigate the degree of crystallization in MTJs consisting of <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><m:mi>Co</m:mi><m:mstyle displaystyle="false" scriptlevel="0"><m:mtext>−</m:mtext></m:mstyle><m:mi>Mn</m:mi><m:mo>/</m:mo><m:mrow><m:mi>Mg</m:mi><m:mi mathvariant="normal">O</m:mi></m:mrow><m:mo>/</m:mo><m:mi>Co</m:mi><m:mstyle displaystyle="false" scriptlevel="0"><m:mtext>−</m:mtext></m:mstyle><m:mi>Mn</m:mi></m:math> in relation to their TMR ratios. Cross-section high resolution transmission electron microscopy reveals that almost consistent lattice constants of these layers for 66 ≤ ≤ 83 with large TMR ratios of 229% at room temperature, confirming the soft nature of the <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><u:mi>Co</u:mi><u:mstyle displaystyle="false" scriptlevel="0"><u:mtext>−</u:mtext></u:mstyle><u:mi>Mn</u:mi></u:math> layer with some dislocations at the <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><z:mrow><z:mi>Mg</z:mi><z:mi mathvariant="normal">O</z:mi></z:mrow><z:mo>/</z:mo><z:msub><z:mi>Co</z:mi><z:mn>75</z:mn></z:msub><z:msub><z:mi>Mn</z:mi><z:mn>25</z:mn></z:msub></z:math> interfaces. calculations confirm the crystalline deformation stability across a broad compositional range in <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><db:mi>Co</db:mi><db:mstyle displaystyle="false" scriptlevel="0"><db:mtext>−</db:mtext></db:mstyle><db:mi>Mn</db:mi></db:math>, proving the advantage of a strain-free interface for much larger TMR ratios.
