Dr. Geoffrey S. D. Beach Profile

Dr. Geoffrey S. D. Beach

Associate Professor at Massachusetts Institute of Technology

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Publications (2)

PROCEEDINGS ARTICLE | September 18, 2018

Current-induced switching and domain wall motion in magnetic insulators with perpendicular anisotropy (Conference Presentation)

Proc. SPIE. 10732, Spintronics XI

KEYWORDS: Iron, Switching, Dielectrics, Magnetism, Terbium, Thulium, Garnet, Europium, Magnons, Anisotropy

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Magnetic insulators (MIs), especially iron-based garnets, possess remarkable properties such as ultralow damping and long magnon decay lengths, which can provide significant advantages for practical applications with respect to their metallic magnetic counterparts. Recently, robust perpendicular magnetic anisotropy (PMA) is obtained in ferrimagnetic films of thulium, europium, and terbium iron garnet (TmIG, EuIG, and TbIG) with high structural quality down to a thickness of 5.6 nm with saturation magnetization close to bulk [1,2]. By using the spin Hall effect in platinum we have demonstrated efficient spin current injection through the TmIG/Pt interface, which we quantified by the spin Hall magnetoresistance and harmonic Hall effect measurements [1-3]. We then achieved deterministic spin-orbit torque-driven magnetization switching of TmIG(~10 nm)/Pt bilayer both with quasi-dc (5 ms) as well as pulsed currents down to 2 ns width[1,4]. The switching current density is found to be of the order of ~10^7 (~10^8) A/cm2 using dc (pulsed) current, comparable to reported values for Pt/Co[5]. We reveal that the threshold switching current strongly depends on the absence or presence of an initially reversed domain in the structure implying a reversal mediated by efficient current-driven domain wall motion. Ultimately, we investigated the current-driven dynamics of domain walls in TmIG. We found that by solely using electrical currents, domain walls can be efficiently moved with very high mobility. Moreover, the flow regime threshold is found to be an order of magnitude lower with respect to conventional ferromagnets with interfacial PMA, owing to structural quality and bulk-like behavior of 7-nm-thick TmIG. These results suggest the utility of PMA rare earth garnets and pave the road towards ultralow dissipation spintronic devices based on MIs. [1] Avci et al., Nat. Mater. 16, 309 (2017); [2]Quindeau et al., Adv. Elec. Mater. 3, 1600376 (2017); [3]Avci et al., PRB 95, 115428 (2017); [4]Avci et al., APL 111, 072406 (2017); [5]Miron et al., Nature 476, 189 (2011).

PROCEEDINGS ARTICLE | October 5, 2015

Spin orbit torques and chiral spin textures in ultrathin magnetic films (Presentation Recording)

Proc. SPIE. 9551, Spintronics VIII

KEYWORDS: Switching, Metals, Video, Microscopy, Magnetism, Platinum, Oxygen, Tantalum, Spintronics, Current controlled current source

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