Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets

TL;DR

This paper investigates MgO/CoFeB/Ta/CoFeB multilayers with variable Ta thickness, demonstrating tunable interlayer exchange from ferromagnetic to antiferromagnetic coupling, crucial for designing synthetic ferrimagnets for data storage.

Contribution

It provides experimental insights into controlling interlayer exchange in CoFeB multilayers by varying Ta thickness, enabling tailored magnetic properties for spintronic applications.

Findings

Tunable interlayer exchange from ferromagnetic to antiferromagnetic with Ta thickness.

Distinct magnetic domain wall structures observed in different coupling regimes.

Implications for data storage device design using synthetic ferri- and antiferromagnets.

Abstract

A study of the multilayer system MgO/CoFeB(1.1nm)/Ta($t$)/CoFeB(0.8nm)/MgO is presented, where the two CoFeB layers are separated by a Ta interlayer of varying thickness $t$. The magnetization properties deduced from complementary techniques such as superconducting quantum interference magnetometry, ferromagnetic resonance frequency measurements and Brillouin light scattering spectroscopy can be tuned by changing the Ta thickness between $t$=0.25 nm, 0.5 nm and 0.75 nm. For $t$=0.5 nm, a ferromagnetic coupling is observed, whereas for t=0.75 nm, the antiferromagnetic coupling needed to construct a synthetic ferrimagnet is realized. In the later case, the shape of magnetic domain walls between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic alignment is very different. This behavior can be interpreted as a result of the change in dipolar as well as interlayer exchange energy and domain wall pinning, which is an important conclusion for the realization of data storage devices based on synthetic ferri- and antiferromagnets.