Realizing an Isotropically Coercive Magnetic Layer for Memristive Applications by Analogy to Dry Friction

Abstract

We investigate the possibility of realizing a spintronic memristive device based on the dependence of the tunnel conductance on the relative angle between the magnetization of the two magnetic electrodes in in-plane magnetized tunnel junctions. For this, it is necessary to design a free layer whose magnetization can be stabilized along several or even any in-plane direction between the parallel and the antiparallel magnetic configurations. We experimentally show that this can be achieved by exploiting antiferromagnet-ferromagnet exchange interactions in a regime where the antiferromagnet is thin enough to induce enhanced coercivity and no exchange bias. The frustration of exchange interactions at the interfaces due to competing ferro-and antiferromagnetic interactions is at the origin of an isotropic dissipation mechanism yielding isotropic coercivity. From a modeling point of view, it is shown that this isotropic dissipation can be described by a dry friction term in the Landau-Lifshitz-Gilbert equation. The influence of this dry friction term on the magnetization dynamics of an in-plane magnetized layer submitted to a rotating in-plane field is investigated both analytically and numerically. The possibility to control the free layer magnetization orientation in an in-plane magnetized magnetic tunnel junction by using the spin transfer torque from an additional perpendicular polarizer is also investigated through macrospin simulation. It is shown that the memristor function can be achieved by the injection of current pulses through the stack in the presence of an in-plane static field transverse to the reference layer magnetization, the aim of which is to limit the magnetization rotation between 0° and 180°.

Isotropically coercive free layer integration in a magnetic tunnel junction for neuromorphic applications

“…2c, confirming the isotropic nature of the free layer. Note that the rounded shape of the loop is expected as a result of dry friction torque due to the F/AF coupling (see [10]).…”

“…As a result, this dissipative mechanism is isotropic. From conceptual point of view, it can be described by a dry friction-like term which can be introduced in the Landau Lifshitz Gilbert equation (for more details [10]).…”

“…The use of an additional inplane field perpendicular to the AL magnetization direction allows limiting the angular excursion of the FL magnetization to ±90° around this transverse field thus insuring the monotonicity of the resistance variation with the polarity of the applied voltage as required for a memristive behavior. A more accurate description of the functionalities of the device is given in [10].…”

Hardware Design for Autonomous Bayesian Networks

“…But design 2 is suitable for Boltzmann networks only and does not work for BNs in general. The synapse in both types of p-circuits is implemented using a resistive crossbar architecture (Alibart et al, 2013 ; Camsari et al, 2017b ), although there are also other types of hardware synapse implementations based on memristors (Li et al, 2018 ; Mahmoodi et al, 2019 ; Mansueto et al, 2019 ), magnetic tunnel junctions (Ostwal et al, 2019 ), spin orbit torque driven domain wall motion devices (Zand et al, 2018 ), phase change memory devices (Ambrogio et al, 2018 ), and so on. In all the simulations, τ S is assumed to be negligible compared to other time scales in the circuit dynamics.…”

Spintronic memristors for neuromorphic circuits based on the angular variation of tunnel magnetoresistance

“…The stabilization of the magnetization of the free layer along different in-plane directions yields the possibility to obtain intermediate resistance values between the lowest and the highest (respectively for parallel and antiparallel alignment of the two magnetizations). Concerning the writing mechanism, in order to discretely rotate the magnetization in the plane, the spin transfer torque (STT) coming from an out-of-plane polarizing layer can be exploited through the application of properly designed pulses 12,13 . In a previous study, we have shown how to realize a free layer able to stabilize the magnetization along different in-plane directions 12,13 .…”