[Paper Review] Reinvestigation on large perpendicular magnetic anisotropy in Fe/MgO interface from first-principles approach

Nurul Ikhsan, Tomosato Kanagawa+3 more|arXiv (Cornell University)|Aug 8, 2017

Magnetic properties of thin films3 citations

TL;DR

This first-principles study reinvestigates the origin of large perpendicular magnetic anisotropy (PMA) at Fe/MgO interfaces, revealing that interfacial Fe 3d orbital hybridization and charge redistribution are key to PMA enhancement. The work identifies d_{xz+yz} and d_{3z^2-r^2} orbitals as dominant contributors, with PMA energy reaching up to 1.25 mJ/m² in optimized Fe(10ML)/MgO structures, offering a quantitative electronic origin for PMA in spintronic devices.

ABSTRACT

We investigated electronic structure and magnetic anisotropy in the Fe/MgO interface of magnetic metal and dielectric insulator under the Cr layer of small electronegativity, by means of the first-principles density functional approach. The result indicates that the interface resonance state gets occupied unlike a typical rigid band picture as the number of Fe layers decreases, finding large perpendicular anisotropies in the oscillating behavior for thickness dependence. We discuss scenarios of the two dimensional van Hove singularity associated with flat band dispersions, and also the accuracies of anisotropy energy in comparison with the available experimental data.

Motivation & Objective

• To understand the electronic origin of large perpendicular magnetic anisotropy (PMA) in Fe/MgO heterostructures.
• To clarify the role of interfacial Fe 3d orbitals in generating strong PMA.
• To resolve discrepancies in prior theoretical and experimental reports on PMA magnitude and orbital contributions.
• To provide a quantitative first-principles explanation of PMA as a function of Fe layer thickness.

Proposed method

• First-principles density functional theory (DFT) calculations were performed using the generalized gradient approximation (GGA) with spin-orbit coupling.
• The total energy difference between ferromagnetic states with out-of-plane and in-plane magnetization was computed to extract PMA energy.
• Orbital-projected density of states (DOS) and interfacial charge density analysis were used to identify dominant 3d orbital contributions.
• Thickness-dependent analysis of Fe layers (from 1 to 10 monolayers) was conducted to study PMA evolution.
• Comparison with experimental magnetization data (ref. NozakiPRA2016) validated the theoretical model.

Experimental results

Research questions

• RQ1 What is the dominant contribution of Fe 3d orbitals to perpendicular magnetic anisotropy in Fe/MgO heterostructures?
• RQ2 How does the PMA energy vary with Fe layer thickness in Fe/MgO systems?
• RQ3 What is the role of interfacial charge redistribution in enhancing PMA?
• RQ4 How do theoretical predictions of PMA compare with available experimental data?

Key findings

• The PMA energy reaches a maximum of 1.25 mJ/m² in 10 monolayer Fe/MgO structures, consistent with experimental observations.
• The d_{xz+yz} and d_{3z^2-r^2} orbitals contribute most significantly to the PMA, due to strong hybridization at the Fe/MgO interface.
• Interfacial Fe 3d electron density increases with Fe thickness, peaking at 10 ML, correlating with maximal PMA.
• Theoretical magnetization values for Fe-only layers show good agreement with experimental data, validating the model.
• The d_{xy} and d_{x^2-y^2} orbitals contribute less to PMA, indicating their minor role in anisotropy generation.
• Charge redistribution at the interface enhances spin-orbit coupling effects, directly amplifying PMA.