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arXiv · 2010.04493

Lattice Softening in Metastable bcc CoxMn100-x(001) Ferromagnetic Layers for a Strain-Less Magnetic Tunnel Junction

Kelvin Elphick·Kenta Yoshida·Tufan Roy·Tomohiro Ichinose·Kazuma Kunimatsu·Tomoki Tsuchiya·Masahito Tsujikawa·Yasuyoshi Nagai·Shigemi Mizukami·Masafumi Shirai·Atsufumi Hirohata
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Abstract

In spintronics, one of the long standing questions is why the MgO-based magnetic tunnel junction (MTJ) is almost the only option to achieve a large tunnelling magnetoresistance (TMR) ratio at room temperature (RT) but not as large as the theoretical prediction. This study focuses on the development of an almost strain-free MTJ using metastable bcc CoxMn100-x ferromagnetic films. We have investigated the degree of crystallisation in MTJ consisting of CoxMn100-x/MgO/CoxMn100-x (x = 66, 75, 83 and 86) in relation to their TMR ratios. Cross-sectional high resolution transmission electron microscopy (HRTEM) reveals that almost consistent lattice constants of these layers for 66 < x < 83 with maintaining large TMR ratios of 229% at RT, confirming the soft nature of the CoxMn100-x layer with some dislocations at the MgO/Co75Mn25 interfaces. For x = 86, on the other hand, the TMR ratio is found to be reduced to 142% at RT, which is partially attributed to the increased number of the dislocations at the MgO/Co86Mn14 interfaces and amorphous grains identified in the MgO barrier. Ab-initio calculations confirm the crystalline deformation stability across a broad compositional range in CoMn, proving the advantage of a strain-free interface for much larger TMR ratios.

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Kelvin Elphick, Kenta Yoshida, Tufan Roy, Tomohiro Ichinose, Kazuma Kunimatsu, Tomoki Tsuchiya, Masahito Tsujikawa, Yasuyoshi Nagai, Shigemi Mizukami, Masafumi Shirai, Atsufumi Hirohata. 2020-10-09. Lattice Softening in Metastable bcc CoxMn100-x(001) Ferromagnetic Layers for a Strain-Less Magnetic Tunnel Junction. https://arxiv.org/abs/2010.04493

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