Abstract
In this paper we report results of improving Co60Fe20B20 interface perpendicular magnetic anisotropy (PMA) by replacing neighbor oxide layer with fluoride one. We expected that fluorine as element with higher than oxide electronegativity could more effectively attract electrons from out-of-plane d orbitals of ferromagnetic, increasing role of in-plane orbitals. By this we wanted to increase PMA and its response to applied voltage bias. Polar magneto-optic Kerr effect measurement show decreasing of out-of-plane magnetic field needed to change magnetization to perpendicular in stacks with oxygen replaced by fluorine as well as increasing of coefficient of response to applied voltage α from < 10 fJ/Vm for CoFeB/Al2O3 interface to 20 fJ/Vm for CoFeB/AlF3/Al2O3 and 22 fJ/Vm for CoFeB/MgF2 stacks. Direct chemical interaction of Co with F was confirmed by x-ray photoelectron spectroscopy (XPS) measurement of Co2p core level region. Moreover angular-resolved XPS showed that F tends to stay at CoFeB interface rather than diffuse out of it.
Highlights
Magnetic random access memory (MRAM), based on tunnel magnetoresistance in magnetic tunnel junctions (MTJ) with perpendicular magnetic anisotropy (PMA) at the ferromagnetic/dielectric interface takes attention in last decade, because of its promising performance as non-volatile memory.[1,2,3] MRAM based on PMA have higher thermal stability and higher integration density than traditional in-plane magnetized memory devices
Common way of changing free ferromagnetic layer magnetization is using spin-transfer torques (STT),[3,4,5,6] but in MTJs with PMA control of magnetization could be provided by applying voltage bias to ferromagnetic/oxide interface.[7,8,9,10]
Partial oxygen replacement by addition of the 0.5 nm-thick AlF3 layer to the CoFeB/Al2O3 interface show decreasing in saturation magnetic field, what indicates increasing of PMA, as shown in the inset of Fig. 1 for the case of physical thickness around 1.1 nm
Summary
Magnetic random access memory (MRAM), based on tunnel magnetoresistance in magnetic tunnel junctions (MTJ) with perpendicular magnetic anisotropy (PMA) at the ferromagnetic/dielectric interface takes attention in last decade, because of its promising performance as non-volatile memory.[1,2,3] MRAM based on PMA have higher thermal stability and higher integration density than traditional in-plane magnetized memory devices. Easy magnetic axis direction of the ferromagnetic layer is determined by resultant of anisotropy energies comparison among three sources of anisotropy: crystalline anisotropy, shape anisotropy and interface anisotropy. Last two anisotropy energies opposition determine the magnetization direction in the ferromagnetic layer [eq 1]
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