Dynamical behaviour of ultrathin [CoFeB (tCoFeB)/Pd] films with perpendicular magnetic anisotropy

Ana S Silva,Simão P Sá,Iñigo J Sola,David Navas,Carlos Garcia,Gleb N Kakazei,Helder Crespo,Sergey A Bunyaev

doi:10.1038/s41598-020-79632-0

Abstract

CoFeB-based ultrathin films with perpendicular magnetic anisotropy are promising for different emerging technological applications such as nonvolatile memories with low power consumption and high-speed performance. In this work, the dynamical properties of [CoFeB (tCoFeB)/Pd (10 Å)]5 multilayered ultrathin films (1 Å ≤ tCoFeB ≤ 5 Å) are studied by using two complementary methods: time-resolved magneto-optical Kerr effect and broadband ferromagnetic resonance. The perpendicular magnetization is confirmed for multilayers with tCoFeB ≤ 4 Å. The effective perpendicular magnetic anisotropy reaches a clear maximum at tCoFeB = 3 Å. Further increase of CoFeB layer thickness reduces the perpendicular magnetic anisotropy and the magnetization became in-plane oriented for tCoFeB ≥ 5 Å. This behaviour is explained by considering competing contributions from surface and magnetoelastic anisotropies. It was also found that the effective damping parameter αeff decreases with CoFeB layer thickness and for tCoFeB = 4 Å reaches a value of ~ 0.019 that is suitable for microwave applications.

Highlights

Since the mid 1970s 1,2, materials with perpendicular magnetic anisotropy (PMA) have been studied for a large diversity of applications including, but not limited to, perpendicular recording m edia[1,2,3,4], patterned magnetic media[5,6], high-density spin-transfer torque magnetic random access memories (STT-MRAM)[7,8,9] and more recently in skyrmion-based d evices[10,11,12] and synthetic antiferromagnets for biomedical a pplications[13,14,15]
Afterwards, several works have been focused on the optimization of the perpendicular magnetic anisotropy (PMA) in CoFeB thin films by using different materials for the capping and/or buffer layers[19], including Ta20,21, Hf22,23, Mo24,25, Ru26,27, V26, Nb27, Pt28,29, Pd30–32 and Au33
Devolder et al.[35] studied the damping parameter of CoxFe80−xB20 ultrathin films and reported that the inhomogeneity term should be constant with the resonance frequency while it should depend on the sample composition, thickness, and materials used for the capping and/or buffer layers

Summary

Introduction

Since the mid 1970s 1,2, materials with perpendicular magnetic anisotropy (PMA) have been studied for a large diversity of applications including, but not limited to, perpendicular recording m edia[1,2,3,4], patterned magnetic media[5,6], high-density spin-transfer torque magnetic random access memories (STT-MRAM)[7,8,9] and more recently in skyrmion-based d evices[10,11,12] and synthetic antiferromagnets for biomedical a pplications[13,14,15]. Devolder et al.[35] studied the damping parameter of CoxFe80−xB20 ultrathin films and reported that the inhomogeneity term should be constant with the resonance frequency while it should depend on the sample composition, thickness, and materials used for the capping and/or buffer layers.

Results

Conclusion