Memristive behavior in magnetoelectric devices

Transcription

1 Memristive behavior in magnetoelectric devices Concepts and Prospects T. Mathurin 1, N. Tiercelin 1, Y. Dusch 1, S. Giordano 1, D. Zakharov 1, V. Preobrazhensky 1 and P. Pernod 1 1 Groupe AIMAN-FILMS, IEMN / LIA LICS

2 Magnetoelectric effect Electrical quantities ME effect Magnetic quantities Mechanical quantities Intrinsic ME effect : weak coupling, cannot be room temperature Artifical ME effect, eg mechanical stress through magnetostriction Voltage piezoelectricity Stress magnetostriction Magnetic effect Practical applications can be considered Magnetostrictive layer Piezoelectric layer 2/11

3 Magnetoresistance to read information Magnetoresistance Reference layer Layer in the middle is either a non-magnetic metal (Giant MR) or insulator (Tunnel MR) Memory layer I(t) I(t) R R ~ 100% with TMR low current Low resistance High resistance Now we know how to read and write 3/11

4 MELRAM : Bistable magnetoelectric cell Concept of MELRAM 1 Magnetoelastic coupling : Magnetization rotation Tensile stress along X (σ > 0) : 0 Mechanical Stress Key advantage : Energy consumption Switching energy ~ 10 aj 0 Compressive stress along X (σ < 0) : S. Giordano, Y. Dusch, N. Tiercelin et al., Europ. Phys. Jour. B. 86, 249 (2013) S. Giordano, Y. Dusch, N. Tiercelin et al., J. Phys. D: Appl. Phys. 46 (2013) N. Tiercelin, Y. Dusch et al. Journal of Applied Physics 109, 07D726 (2011) N. Tiercelin, Y. Dusch, A. Klimov, S. Giordano, Applied Physics Letters 99, (2011). Y. Dusch, N. Tiercelin, A. Klimov, S. Giordano, Journal of Applied Physics 113, 17C719 (2013). 1 N. Tiercelin, Y. Dusch, V. Preobrazhensky, P. Pernod, Mémoire magnétoélectrique (MELRAM), FR (A1) Magnetoelectric Memory, Extension PCT WO/2011/ /11

5 Electrical behavior dynamics v v f = 100 MHz i PMN-PT <011> i R(q) C High R Low R Bistability means impossible to control magnetization step by step Sacrificing bistability for continuous angular magnetization control Explorable area Can t have both hysteresis and continuous resistance variation Let s look at devices with a domain walls 5/11

6 New device Very same concept, but with a two-domain configuration Chanthbouala et al. Nature Physics, 2011 H 0 σ > 0 m 1 m 2 σ < 0 m 1 m 2 DW motion and ejection I(t) I(t) 6/11

7 Variable section Results : DW motion with intermediate states Hysteresis is almost surely a numerical artifact. Anyway, experimentally there will be sources of irreversibility Stays in any given state only if stress in maintained because of perfectly smooth profile Pinning site 7/11

8 Understanding the underlying physics We consider a one-dimensional ferromagnet with two domains Let s write the total energy of our system m θ H 0 E tot = V (e uni + e Zeeman + e exch + e stress )dv Applied stress E tot = L 2 L 2 S x e tot (x)dx S is the section, various profiles can be tested m 1 m 2 x We can either : - solve for θ x minimizing the energy - Extract DW position from equilibrium criteria Two simple, complementary models 8/11

9 1D model results Equilibrium condition gives final DW position Solving for θ Ideally, x p gives resulting resistance No hysteresis here 9/11

10 Magnetoelectric memristor Stud geometry needed Voltage controlled memristor (sub 1V) Step by step operation Significant maximum conductance contrast (80-90%) Unequivocal operation given sign of V Energy efficient MELRAM switching energy ~ 10 3 kt < 10 aj! ~ compatible with crossbar geometries V 0 PMN-PT Key advantage is energy consumption Appropriate for power-aware computing E d E d,elec E d,mag 10/11

11 Experimental realization What has been done : - Successful lift-off for electrodes on PMN-PT - 5µm-wide piezo stud, w/ Focused Ion Beam In parallel : - Further geometrical design optimization - Finding best magnetic parameters compromise - Electronic lithography on plain PMN-PT Next : Plasma etching instead of FIB to scale the process - Plan to build a magneto-optical microscope to look at magnetic domains 11/11

12 THANK YOU FOR YOUR ATTENTION The idea is to move a domain wall with mechanical stress