Inductive determination of the optimum tunnel barrier thickness in magnetic tunneling junction stacks for spin torque memory applications

Abstract

We use pulsed inductive microwave magnetometry to study the precessional magnetization dynamics of the free layer in CoFeB/MgO/CoFeB based magnetic tunneling junction stacks with varying MgO barrier thickness. From the field dependence of the precession frequency we are able to derive the uniaxial anisotropy energy of the free layer and the exchange coupling between the free and the pinned layer. Furthermore the field dependence of the effective damping parameter is derived. Below a certain threshold barrier thickness we observe an increased effective damping for antiparallel orientation of free and pinned layer which would inhibit reversible low current density spin torque magnetization reversal. Such inductive measurements, in combination with wafer probe station based magneto transport experiments, allow a fast determination of the optimum tunnel barrier thickness range for spin torque memory applications in a lithography free process.

Metalliclike behavior of the exchange coupling in (001) Fe/MgO/Fe junctions

“…We point out that a weaker ferromagnetic coupling (<0.03 erg/cm 2 ) has also been * christine.bellouard@univ-lorraine.fr reported for MgO thicknesses close to 1 nm [9,10,24]. In the case of sputtered junctions, a ferromagnetic coupling has been observed in the planar magnetic configuration with an exponential MgO thickness dependence [13,17], and has therefore been attributed to a cooperative electronic effect. Nevertheless, an antiferromagnetic coupling (<0.1 erg/cm 2 ) has been observed recently with a sputtered planar multilayer with a quite large MgO thickness (1.6 nm) [23].…”

“…This approach, firstly used to interpret the Fe/MgO AF coupling because of its strong thickness dependence [9], is now dismissed [10] as this model is not valid for such a thin barrier. It has been more satisfactorily applied in the case of planar or perpendicular junctions with a thicker barrier [17]. Nevertheless, the temperature dependence predicted by Bruno [2,27] in the case of an insulating barrier has never been clearly observed.…”

“…On the contrary, for a semiconducting or insulating spacer [3][4][5][6][7][8], magnetic properties seem to depend deeply on growth conditions and then on structural specifications. Among them, the MgO spacer [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] appears unique in presenting a large variety of experimental results. They concern either the MgO thickness range and the coupling sign and strength, or the junction magnetic geometry (planar or perpendicular magnetization).…”

Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions

“…17 To analyze the double resonance mode in sample S3 in more detail, we performed macrospin simulations using the model presented in Ref. 18. This model, based on the Stoner-Wolfarth approach, assumes coherent rotation of the FL and RL magnetization.…”

Broadband ferromagnetic resonance characterization of GaMnAs thin films

“…Over the last years broadband vector network analyzer based ferromagnetic resonance (VNA-FMR) 18 using coplanar wave guides as inductive antennas has become a versatile tool for the simple and fast all electrical characterization of precessional dynamics of various magnetic thin films and multilayers 19,20 . In principle low-temperature VNA-FMR 21 should also be suitable for the electrical characterization of ferromagnetic semiconductors such as GaMnAs.…”