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Origin of the large voltage-controlled magnetic anisotropy in a Cr/Fe/MgO junction with an ultrathin Fe layer: First-principles investigation

Voltage-controlled magnetic anisotropy (VCMA) has attracted broad interest due to its high efficiency in switching magnetization. Large VCMA was experimentally observed in Cr/Fe/MgO junction with ultrathin Fe layer [Nozaki et al., Phys. Rev. Appl. 5, 044006 (2016)], whose underlying mechanism was st...

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Published in:Physical review. B 2020-04, Vol.101 (14), p.1, Article 144434
Main Authors: Chen, W. Z., Jiang, L. N., Yan, Z. R., Zhu, Y., Wan, C. H., Han, X. F.
Format: Article
Language:English
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Summary:Voltage-controlled magnetic anisotropy (VCMA) has attracted broad interest due to its high efficiency in switching magnetization. Large VCMA was experimentally observed in Cr/Fe/MgO junction with ultrathin Fe layer [Nozaki et al., Phys. Rev. Appl. 5, 044006 (2016)], whose underlying mechanism was still not clear however. The Cr/Fe/MgO/Fe magnetic tunnel junction (MTJ) is also well known for its quantum-well (QW) states and as-induced spin-dependent resonant tunneling [Greullet et al., Phys. Rev. Lett. 99, 187202 (2007)]. Here, in order to uncover the relation between the large VCMA and the QW states, we developed a k-resolved VCMA calculation method combined with the second-order perturbation theory to investigate it. We find the VCMA coefficient reaches −297 fJ/V m matching well with the previous experiment with three monolayers (MLs) of Fe. The coefficient oscillates strongly and even changes its sign with increasing the number of Fe MLs. Comparing the k-resolved VCMA with the Fermi surface of the interfacial Fe atom, the screening charges theory for VCMA was verified. For 2–9 MLs Fe, interestingly, the QW states of Δ1 electron at the Γ point provide large (no) contribution to the VCMA with odd (even) MLs. Moreover, the change of the orbital-resolved Fermi surface at the interfacial Fe atom also plays an important role on VCMA oscillation, which as well as the QW states results in the largest VCMA for 3-ML Fe. Our results deepen the understanding of the large VCMA in the Cr/Fe/MgO junction, which would be helpful to design a practical MTJ with large VCMA.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.101.144434