Pt/Co/oxide and oxide/Co/Pt electrodes for perpendicular magnetic tunnel junctions

Abstract

This letter presents a study of perpendicular magnetic anisotropy in oxide/Co/Pt structures, which could constitute the upper magnetic electrode of magnetic tunnel junctions. The growth of cobalt layers on SiO2 substrates shows that all 0.6 nm thick Co films are superparamagnetic, whereas perpendicular magnetic anisotropy is obtained for 1.5 nm films after annealing. Co layers grown on various Al and Mg oxides prepared by sputtering also exhibit perpendicular magnetic anisotropy after annealing. Combined with inverse Pt/Co(CoFeB)/oxide stackings, these structures allow preparing tunnel junctions with thicker magnetic electrodes and much better thermal stability than those based on standard Pt/Co multilayers.

Perpendicular Magnetic Anisotropy in CoFeB/Pd Bilayers

“…For the thinnest magnetic layers (0.4 nm), is 40 mT in the case of Co and 4 mT in the case of CoFeB. The order of magnitude difference is similar to [10].…”

“…These layers do not induce a strong interfacial anisotropy, like Pt or Pd, in the as-deposited state. Nevertheless, Nistor et al recently demonstrated that it is possible to stabilize PMA in thin layers of CoFeB grown on a buffer layer of MgO capped by Pt after annealing at 350 [10]. It has also been shown that with high temperature annealing, it is possible to stabilize PMA with underlayers and this is attributed to the hybridization of the Co and O orbitals after high-temperature annealing [11].…”

Perpendicular magnetic anisotropy of Co\Pt bilayers on ALD HfO2

“…Nistor et al 8 report on SiO 2 \Co\Pt trilayers and conclude that annealing can modify the magnetic anisotropy of Pt capped Co thin films deposited on an amorphous template from in-plane to perpendicular. The HfO 2 \Co\Pt trilayers reported here show the same annealing behaviour (although for lower annealing temperatures), which can similarly be ascribed to the amorphous nature of HfO 2 .…”

“…4 HfO 2 on the other hand is amorphous. Co\Pt bilayer structures have already been studied on other amorphous oxides like SiO 2 by Nistor et al 8 They report that an annealing temperature from 250 C to 400 C can modify the Magnetic Anisotropy (MA) of a thin Co film from in-plane (IP) to perpendicular (PMA). The oxygen atoms at the interface between Co and the oxide may also contribute to the appearance of PMA, through hybridization of the Co 3 d z orbitals with the oxide 2p xy(yz) orbitals.…”

Interface induced perpendicular magnetic anisotropy in a Co/CoO/Co thin-film structure: anin situMOKE investigation

“…Hysteresis loop of the F3-film was also measured ex-situ under higher applied magnetic field and is given in fig.1 It is important to note that hybridization is localized at the interfaces and therefore, even with oxygen mediated interfaces (as mentioned above), significant PMA is observed only in ultra thin magnetic layer ranging from fewÅ to a few tens ofÅ. 8,9 In the present work, PMA in 104Å thick Co layer is some what surprising and can not be understood only in-terms of interface hybridization.…”