Abrupt Transition from Ferromagnetic to Antiferromagnetic of Interfacial Exchange in Perpendicularly MagnetizedL10-MnGa/FeCo Tuned by Fermi Level Position

Abstract

An abrupt transition of the interfacial exchange coupling from ferromagnetic to antiferromagnetic was observed in the interface of perpendicularly magnetized L10-MnGa/Fe1-xCox epitaxial bilayers when x was around 25%. By considering the special band structure of the MnGa alloy, we present a model explaining this transition by the spin-polarization reversal of Fe1-xCox alloys due to the rise of the Fermi level as the Co content increases. The effect of interfacial exchange coupling on the coercive force (Hc) and the spin-dependent tunneling effect in perpendicular magnetic tunnel junctions (pMTJs) based on the coupled composite were also studied. Changes from the normal spin valve to inverted magnetoresistance loops corresponding to the coupling transition were observed in pMTJs with MnGa/Fe1-xCox as an electrode.

Antiferromagnetic coupling in perpendicularly magnetized cubic and tetragonal Heusler bilayers

“…The absolute values of negative J ex are comparable to those evaluated in the FeCo/MnGa bilayers [9] and larger than those in Co 2 FeSi (Al)/MnGa [12].…”

“…An excellent candidate for satisfying these properties is MnGa alloys [2,3]. The structural, magnetic, and transport properties as well as spin polarization and magnetization dynamics of MnGa with PMA have been investigated in previous studies [4][5][6][7][8][9]. The new challenge concerning to MnGa alloys is increasing the tunnel magnetoresistance (TMR) ratio based on MgOMTJs.…”

“…Interestingly, the magnetic Jex was found to be antiferromagnetic (AF) for a Co-rich interlayer, when FeCo alloy interlayer was introduced [9]. AF coupling is very rare in magnetic films with PMA and is technologically important for achieving synthetic ferrimagnetic structure for STT-MRAM.…”

“…The new challenge concerning to MnGa alloys is increasing the tunnel magnetoresistance (TMR) ratio based on MgOMTJs. One effective way is to insert an ultra-thin ferromagnetic metal/alloy interlayer such as Fe [7], Co, and FeCo [9] between the MnGa and MgO barrier.…”

Perpendicularly magnetized ferrimagnetic [Mn50Ga50/Co2FeAl] superlattice and the utilization in magnetic tunnel junctions

“…Thus, an inverted R(H) is observed in the experiment. 22,23 The MR ratio calculated from (R max -R min )/R min × 100% is 1.3%, where R max,min denotes the maximum and minimum resistance values of the pMTJ. The low MR ratio is possibly originated from the the Mn element diffusion during the high temperature annealing.…”