Eur. Phys. J. B (2013) 86: 110
https://doi.org/10.1140/epjb/e2013-30680-8

Regular Article

Controlling the demagnetizing field of an in-plane free layer by exchange coupling with a perpendicular multilayer^*

School of Physics and CRANN, Trinity College, Dublin 2, Ireland

^a e-mail: lauyc@tcd.ie

Received: 24 July 2012
Received in final form: 12 December 2012
Published online: 20 March 2013

Abstract

The demagnetizing field of a Co₅₀Fe₅₀ free layer in an in-plane micron-sized magnetic tunnel junction (MTJ) can be partially compensated by exchange coupling with a [Co₉₀Fe₁₀/Pt]_N multilayer with perpendicular magnetic anisotropy via a Ru interlayer. The perpendicular anisotropy for N = 5 is optimized for nominal CoFe and Pt thickness of 0.4 nm and 1.0 nm, respectively. An increase of tunnel magnetoresistance (TMR) from 2% to 75% is observed in MTJs as the free layer thickness, t varies from 1.0 nm to 3.0 nm. A phenomenological model is developed to interpret the TMR dependence in terms of the free layer magnetization rotation from in-plane to out-of-plane with decreasing t, a consequence of interlayer exchange coupling with the perpendicular multilayer. We suggest that this strategy could significantly reduce the switching current density in such MTJs.