Fully epitaxial fcc(111) magnetic tunnel junctions with a Co90Fe10/MgAlO/Co90Fe10 structure

TL;DR

This paper demonstrates the fabrication of fully epitaxial fcc(111) magnetic tunnel junctions using CoFe and MgAlO, achieving high-quality interfaces and notable tunnel magnetoresistance ratios, thus broadening the material options for spintronic devices.

Contribution

It introduces a novel fcc(111)-type MTJ structure with epitaxial growth on Ru buffers, expanding beyond traditional (001)-type MTJs and showing promising interface stability and performance.

Findings

Achieved epitaxial growth of CoFe/MAO/CoFe trilayers on Ru buffers.

Observed a tunnel magnetoresistance ratio of 37% at room temperature.

Confirmed sharp interfaces and nearly identical interface qualities on both sides.

Abstract

Magnetic tunnel junctions (MTJs) with bcc(001)-type structures such as Fe(001)/MgO(001)/Fe(001), have been widely used as the core of various spintronic devices such as magnetoresistive memories; however, the limited material selection of (001)-type MTJs hinders the further development of spintronic devices. Here, as an alternative to the (001)-type MTJs, an fcc(111)-type MTJ using a fully epitaxial CoFe/rock-salt MgAlO (MAO)/CoFe is explored to introduce close-packed lattice systems into MTJs. Using an atomically flat Ru(0001) epitaxial buffer layer, fcc(111) epitaxial growth of the CoFe/MAO/CoFe trilayer is achieved. Sharp CoFe(111)/MAO(111) interfaces are confirmed due to the introduction of periodic dislocations by forming a 5:6 in-plane lattice matching structure. The fabricated (111) MTJ exhibits a tunnel magnetoresistance ratio of 37% at room temperature (47% at 10 K). Symmetric differential conductance curves with respect to bias polarity are observed, indicating the achievement of nearly identical upper and lower MAO interface qualities. Despite the charge-uncompensated (111) orientation for a rock-salt-like MAO barrier, the achievement of flat, stable, and spin-polarized barrier interfaces opens a promising avenue for expanding the design of MTJ structures.