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Title: Influence of boron diffusion on the perpendicular magnetic anisotropy in Ta|CoFeB|MgO ultrathin films

We have studied structural and magnetic properties of Ta|CoFeB|MgO heterostructures using cross-section transmission electron microscopy (TEM), electron energy loss spectrum (EELS) imaging, and vibrating sample magnetometry. From the TEM studies, the CoFeB layer is found to be predominantly amorphous for as deposited films, whereas small crystallites, diameter of ∼5 nm, are observed in films annealed at 300 °C. We find that the presence of such nanocrystallites is not sufficient for the occurrence of perpendicular magnetic anisotropy. Using EELS, we find that boron diffuses into the Ta underlayer upon annealing. The Ta underlayer thickness dependence of the magnetic anisotropy indicates that ∼0.2 nm of Ta underlayer is enough to absorb the boron from the CoFeB layer and induce perpendicular magnetic anisotropy. Boron diffusion upon annealing becomes limited when the CoFeB layer thickness is larger than ∼2 nm, which coincides with the thickness at which the saturation magnetization M{sub S} and the interface magnetic anisotropy K{sub I} drop by ∼20%. These results show the direct role which boron plays in determining the perpendicular magnetic anisotropy in CoFeB|MgO heterostructures.
Authors:
; ; ; ; ; ;  [1]
  1. National Institute for Materials Science, Tsukuba 305-0047 (Japan)
Publication Date:
OSTI Identifier:
22412995
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 4; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ANISOTROPY; ANNEALING; BORON; COBALT COMPOUNDS; DIFFUSION; ELECTRONS; ENERGY-LOSS SPECTROSCOPY; HETEROJUNCTIONS; INTERFACES; IRON BORIDES; LAYERS; MAGNESIUM OXIDES; MAGNETIC PROPERTIES; MAGNETIZATION; TANTALUM; THIN FILMS; TRANSMISSION ELECTRON MICROSCOPY