Tailoring magnetic properties of CoFeB films via tungsten buffer and capping layers

TL;DR

This study investigates how tungsten buffer and capping layers, combined with annealing, can be used to tailor the magnetic anisotropy and structural properties of CoFeB films for spintronic applications.

Contribution

It provides a systematic analysis of the effects of W buffer and capping layers, and annealing temperature, on the magnetic and structural properties of CoFeB films, revealing pathways to enhance thermal stability.

Findings

W buffer layers induce crystallization of CoFeB during annealing.

Annealing at 400°C significantly increases uniaxial magnetic anisotropy.

Surface morphology and grain size are altered by W layers and annealing temperature.

Abstract

Controlling the interface between W and CoFeB-based buffer or capping layers at an appropriate temperature is essential for modifying the strength of magnetic anisotropy. In this work, we systematically explore the impact of W buffer and capping layers on the structural, topological, and magnetic anisotropy properties of W (5 nm)/CoFeB(10 nm) and CoFeB(10 nm)/W(3 nm) bilayers sputtered at room temperature (RT) and annealed at an optimal annealing temperature (TA) of 400 C. Our findings demonstrate that the bilayer films uniaxial magnetic anisotropy (UMA) with out-of-plane coercivity (Hcp) is highly influenced by the W buffer, capping layers, and TA. Specifically, the Hcp of the CoFeB layer with the buffer and capping layers annealed at 400 C samples exceed several times the coercivity of those unannealed. CoFeB buffered with W and annealed at 400 C shows larger Hcp, two-fold UMA, and higher in-plane UMA energy density (Keff) than the CoFeB/W bilayers, which can be attributed to the W buffer layer inducing the crystallization of CoFeB during annealing. The W buffer, capping layers, and the TA for W and CoFeB-based bilayer samples significantly alter the surface morphology, grain sizes, and surface roughness. The XRD analysis reveals nano-crystallites embedded in the larger grains of the 400 C annealed samples. Hence, this work offers a promising approach to achieving high thermal stability of UMA in W and CoFeB-based spintronic applications.