About

Professor Geoffrey S.D. Beach is the Toyota Professor in Materials Processing and a Professor of Materials Science and Engineering at MIT. His research focuses on spin dynamics and 'spin-electronics,' which involves studying new materials whose magnetic properties can be changed electrically, particularly in nanoscale magnetic materials and devices. His work aims to develop methods for more densely storing information and accessing it more quickly by understanding the magnetization configurations in nanoscale structures and their evolution. A significant aspect of his research involves harnessing the electron's spin in magnetic materials to create new approaches to spin-based storage and computation. To achieve this, his group develops advanced optical and electrical instrumentation capable of probing magnetization dynamics at the shortest timescales and smallest length scales, enabling the development of new materials and structures to meet future information storage and processing demands.

Research topics

• Condensed matter physics
• Physics
• Quantum mechanics
• Materials science
• Computer Science
• Optics
• Nanotechnology
• Classical mechanics
• Theoretical physics
• Mathematics
• Geometry
• Mathematical analysis

Selected publications

• Visualizing a Terahertz Superfluid Plasmon in a Two-Dimensional Superconductor

  ArXiv.org · 2025-06-09

  preprintOpen access

  The superconducting gap defines the fundamental energy scale for the emergence of dissipationless transport and collective phenomena in a superconductor. In layered high-temperature cuprate superconductors, where the Cooper pairs are confined to weakly coupled two-dimensional copper-oxygen planes, terahertz (THz) spectroscopy at sub-gap millielectronvolt energies has provided crucial insights into the collective superfluid response perpendicular to the superconducting layers. However, within the copper-oxygen planes the collective superfluid response manifests as plasmonic charge oscillations at energies far exceeding the superconducting gap, obscured by strong dissipation. Here, we present spectroscopic evidence of a below-gap, two-dimensional superfluid plasmon in few-layer Bi2Sr2CaCu2O8+x and spatially resolve its deeply sub-diffractive THz electrodynamics. By placing the superconductor in the near-field of a spintronic THz emitter, we reveal this distinct resonance-absent in bulk samples and observed only in the superconducting phase-and determine its plasmonic nature by mapping the geometric anisotropy and dispersion. Crucially, these measurements offer a direct view of the momentum- and frequency dependent superconducting transition in two dimensions. These results establish a new platform for investigating superfluid phenomena at finite momenta and THz frequencies, highlighting the potential to engineer and visualize superconducting devices operating at ultrafast THz rates.

  PublisherOA PDFDOI

• Néel domain walls with bistable chirality in a perpendicularly magnetized ferrimagnetic insulator

  Nature Communications · 2025-06-04 · 1 citations

  articleOpen accessSenior author

  Field-free spin-orbit torque-driven domain wall motion in magnetic thin films with perpendicular magnetic anisotropy (PMA) requires the domain walls to have Néel character. Conventionally, Néel domain walls are stabilized by the Dzyaloshinskii-Moriya interaction (DMI) in ultrathin films. Here, in a europium iron garnet thin film with PMA and an additional uniaxial in-plane anisotropy, we demonstrate two bistable Néel domain wall states in the absence of DMI, and the capability to toggle the wall states with an in-plane field pulse and consequently their directions of motion under a current pulse. We present a phase diagram for the bistable Néel domain wall states as a function of in-plane field pulse width and amplitude. By fitting the experimental data to an analytical model of Néel wall reversal through the nucleation and propagation of Bloch lines, we extract the length of the initial reversed domain wall segment and Bloch line nucleation energy barrier. Current-driven motion of in-plane anisotropy stabilized Néel walls is qualitatively different from that of DMI-stabilized ones owing to the different symmetry of the effective fields that stabilize the Néel configuration. Furthermore, we present a proof of principle demonstration for 2-bit random number generation based on the stochastic reversal of domain wall chirality. These results provide critical insight into the topological energy barrier of Bloch lines and identify paths towards domain wall-based memory and computing devices. Neel domain walls are typically stabilized by an interfacial Dzyaloshinskii-Moriya interaction, with a chirality that is fixed by the sample materials. Here, Song, Huang and coauthors demonstrate the existence of two bistable Néel domain wall states with opposite chiralities, and the switching between these via magnetic field pulses

  PublisherOA PDFDOI

• Field-free switching of perpendicular magnetization in a ferrimagnetic insulator with spin reorientation transition

  Science Advances · 2025-08-22

  articleOpen accessSenior authorCorresponding

  Writing magnetic bits through spin-orbit torque (SOT) switching is promising for fast and efficient magnetic random-access memory devices. While SOT switching of out-of-plane (OOP) magnetized states requires lateral symmetry breaking, in-plane (IP) magnetized states suffer from low storage density. Here, we demonstrate a field-free switching scheme using a 5-nanometer europium iron garnet film grown with a (110) orientation that shows a spin reorientation transition from OOP to IP above room temperature. This scheme combines the benefits of high-density storage in the OOP states at room temperature and the efficient field-free SOT switching in the IP states at elevated temperatures. While conventional switching of OOP bits faces the dilemma that high OOP anisotropy is required to improve bit stability and low OOP anisotropy is required to lower switching current density, this scheme disentangles this interdependence, allowing for low switching currents to be possible without sacrificing the bit stability, offering opportunities for future memory devices.

  PublisherDOI

• Unveiling geometrically tunable spin superfluidity and nonlocal Spin hall magnetoresistance in lateral devices

  2024-10-04

  articleSenior author
  PublisherDOI

• Temperature‐Dependent Surface Anisotropy in (110) Epitaxial Rare Earth Iron Garnet Films

  Small · 2024-10-21 · 3 citations

  articleOpen accessCorresponding

  Ferrimagnetic oxide thin films are important material platforms for spintronic devices. Films grown on low symmetry orientations such as (110) exhibit complex anisotropy landscapes that can provide insight into novel phenomena such as spin-torque auto-oscillation and spin superfluidity. Using spin-Hall magnetoresistance measurements, the in-plane (IP) and out-of-plane (OOP) uniaxial anisotropy energies are determined for a thickness series (5-50 nm) of europium iron garnet (EuIG) and thulium iron garnet (TmIG) films epitaxially grown on a gadolinium gallium substrate with (110) orientation and capped with Pt. Pt/EuIG/GGG exhibits an (001) easy plane of magnetization perpendicular to the substrate, whereas Pt/TmIG/GGG exhibits an (001) hard plane of magnetization perpendicular to the substrate with an IP easy axis. Both IP and OOP surface anisotropy energies comparable in magnitude to the bulk anisotropy are observed. The temperature dependence of the surface anisotropies is consistent with first-order predictions of a simplified Néel surface anisotropy model. By taking advantage of the thickness and temperature dependence demonstrated in these ferrimagnetic oxides grown on the low symmetry (110) orientations, the complex anisotropy landscapes can be tuned to act as a platform to explore rich spin textures and dynamics.

  PublisherOA PDFDOI

• Ionic Modulation of Ferromagnetic and Proximity‐Induced Magnetization in Co/Pd Heterostructures

  Advanced Functional Materials · 2024-06-10 · 5 citations

  articleOpen accessSenior author

  Abstract Despite the rampant discovery of tunable magnetic properties using magneto‐ionic gating, e.g., magnetic anisotropy, exchange bias, and exchange interactions, there are few studies that give a quantitative understanding of the reversible and irreversible effects of ionic infiltration. In this study, in situ vibrating sample magnetometry, superconducting quantum interference device magnetometry, and X‐ray magnetic circular dichroism (XMCD) reveal the reversible and irreversible control of magnetization, anisotropy, proximity‐effects, spin, and orbital angular momenta. Pd/Co/Pd trilayers, loaded using solid‐state hydrogen‐ion gating, show a decrease in the saturation magnetization of Co, and an increase in the proximity‐induced moment of Pd. This results in little to no change in the net effective magnetization, yet, allows for the effective anisotropy to be reversibly controlled by 270 kJ m −3 . The reversible control of the effective anisotropy is dominated by a reversible change in surface anisotropy, however, under repeated cycling, irreversible evolution occurs in the heterostructure. XMCD measurements indicate this is partly due to hydrogen‐induced modification of the spin and orbital angular momenta. Together, these measurements indicate that the origin of the reversible and irreversible effects of magneto‐ionic gating is interfacial and provides crucial insight to scale and optimize thin film heterostructures for enhanced longevity and faster response time.

  PublisherOA PDFDOI

• Temperature and bias voltage dependences of magnetic tunnel junction with FeAlSi electrode

  APL Materials · 2024-02-01 · 6 citations

  articleOpen access

  We fabricated magnetic tunnel junctions (MTJs) with FeAlSi free layers and investigated the tunnel magnetoresistance (TMR) properties. We found that the temperature and bias voltage dependences of the TMR effect in FeAlSi-MTJs were almost the same as MTJs with Fe free layers despite the low Curie temperature of FeAlSi. In the inelastic electron tunneling spectroscopy measured at low temperatures, the relatively large cutoff energy of magnon excitation at the FeAlSi and MgO interface was confirmed. In addition, we studied for the first time the exchange stiffness constant of FeAlSi films by Brillouin light scattering. The determined value of the stiffness constant of FeAlSi was 14.3 (pJ/m), which was similar to that of Fe. Both the large magnon cutoff at the interface and the stiffness constant of FeAlSi are considered to be the reason for the good temperature and voltage dependences of FeAlSi-MTJs.

  PublisherOA PDFDOI

• Damping and Interfacial Dzyaloshinskii–Moriya Interaction in Thulium Iron Garnet/Bismuth-Substituted Yttrium Iron Garnet Bilayers

  ACS Applied Materials & Interfaces · 2024-01-05 · 12 citations

  article

  Thin films of ferrimagnetic iron garnets can exhibit useful magnetic properties, including perpendicular magnetic anisotropy (PMA) and high domain wall velocities. In particular, bismuth-substituted yttrium iron garnet (BiYIG) films grown on garnet substrates have a low Gilbert damping but zero Dzyaloshinskii–Moriya interaction (DMI), whereas thulium iron garnet (TmIG) films have higher damping but a nonzero DMI. We report the damping and DMI of thulium-substituted BiYIG (BiYTmIG) and TmIG|BiYIG bilayer thin films deposited on (111) substituted gadolinium gallium garnet and neodymium gallium garnet (NGG) substrates. The films are epitaxial and exhibit PMA. BiYIG|TmIG bilayers have a damping value that is an order of magnitude lower than that of TmIG, and BiYIG|TmIG|NGG have DMI of 0.0145 ± 0.0011 mJ/m2, similar to that of TmIG|NGG. The bilayer therefore provides a combination of DMI and moderate damping, useful for the development of high-speed spin orbit torque-driven devices.

  PublisherDOI

• Atomic order of rare earth ions in a complex oxide: a path to magnetotaxial anisotropy

  Nature Communications · 2024-06-14 · 11 citations

  articleOpen access

  Abstract Complex oxides offer rich magnetic and electronic behavior intimately tied to the composition and arrangement of cations within the structure. Rare earth iron garnet films exhibit an anisotropy along the growth direction which has long been theorized to originate from the ordering of different cations on the same crystallographic site. Here, we directly demonstrate the three-dimensional ordering of rare earth ions in pulsed laser deposited (Eu x Tm 1-x ) 3 Fe 5 O 12 garnet thin films using both atomically-resolved elemental mapping to visualize cation ordering and X-ray diffraction to detect the resulting order superlattice reflection. We quantify the resulting ordering-induced ‘magnetotaxial’ anisotropy as a function of Eu:Tm ratio using transport measurements, showing an overwhelmingly dominant contribution from magnetotaxial anisotropy that reaches 30 kJ m −3 for garnets with x = 0.5. Control of cation ordering on inequivalent sites provides a strategy to control matter on the atomic level and to engineer the magnetic properties of complex oxides.

  PublisherOA PDFDOI

• Measurement of Kerr rotation and ellipticity in magnetic thin films by MOKE magnetometry

  Journal of Applied Physics · 2024-02-08 · 7 citations

  articleOpen accessSenior author

  When polarized light is incident on a magnetic material, the magneto-optical Kerr effect (MOKE) rotates the polarization and induces ellipticity in the reflected light, which allows the magnetization direction to be probed optically. The Kerr rotation and ellipticity determine the magnitude of the effect and are usually measured using dedicated ellipsometers. Here, we demonstrate a simple method for extracting Kerr rotation and ellipticity in magnetic thin films using a conventional MOKE magnetometer consisting of two polarizers and a quarter waveplate. Using this technique, we report the longitudinal Kerr angle of BiYIG, GdCo, and TbCo. We additionally observe a linear decrease in polar complex Kerr angle magnitude in 3 nm GdCo films as the atomic fraction of Gd is increased.

  PublisherOA PDFDOI

Recent grants

• Electric Field Control of Spin Dynamics in Metal Spintronic Devices

  NSF · $348k · 2011–2014

• Electrical switching of magnetic devices by voltage-controlled proton insertion for low-power, high-performance data storage and computing

  NSF · $360k · 2018–2021

• Spin Orbitronics: Interfacial Design of Spintronic Materials and Devices

  NSF · $360k · 2014–2017

• MIT Materials Research Science and Engineering Center - Full Proposal

  NSF · $16.4M · 2014–2021

Frequent coauthors

• Felix Büttner

  50 shared

• Can Onur Avci

  Institut de Ciència de Materials de Barcelona

  39 shared

• Maxwell Mann

  38 shared

• Lucas Caretta

  Brown University

  37 shared

• Ivan Lemesh

  Massachusetts Institute of Technology

  30 shared

• Caroline A. Ross

  29 shared

• R. P. Vasquez

  27 shared

• Kai Litzius

  25 shared

Education

• Ph.D., Materials Science and Engineering

  Massachusetts Institute of Technology

  1990

• M.S., Materials Science and Engineering

  Massachusetts Institute of Technology

  1986

• B.S., Materials Science and Engineering

  Massachusetts Institute of Technology

  1984

Awards & honors

• 2023 Fellow, IEEE
• 2009 Junior Bose Award