Project Overview

There has been a surge of interest in the field of multiferroic devices, which enable control of magnetism using voltage instead of the traditional method of current-based control of magnetism. This interest is spurred partly by the emergence of electric-field driven, stain-mediated magnetoelectric (ME) coupling in ferroelectric and ferromagnetic materials. This strain-mediated ME coupling is tunable by an applied electric field, at the core of designing new multiferroic devices, such as miniature antennas, nanoscale memories, magnetic field sensors, and motors. Our group has focused on understanding and utilizing the dynamics of magnetic domain of strain-mediated multiferroic materials, from both the modeling and experimental perspectives, with the goal of realizing a submicron multiferroic motor for a range of applications. Working jointly with researchers from the TANMS research center, we characterize the fundamental physical properties of our devices using the beamlines at the Advanced Light Source, Lawrence Berkeley National Laboratory. Collaborating with researchers from biomedical engineering, we work on navigating and precisely controlling magnetically-tagged cells and particles using these motor arrays in a microfluidic environment for localized capturing and sorting purposes.

During my Ph.D., I have gained expertise in design, modeling, fabrication, characterization and testing of composite multiferroic systems. I have conducted not only fundamental research work on complex material property characterization (including using different magnetometry methods and synchrotron x-ray beamline experiments to characterize magnetic and ferroelectric properties) but also application-based research of systems that integrate multiferroics and microfluidics (in close collaboration with material science and bioengineering researchers).
1. I worked on finite element simulation to compare the unidirectional and bidirectional coupled multiferroic models to show the nonnegligible importance of considering the bidirectional coupling in systems with increasingly popular highly magnetoelastic materials, such as Terfenol-D. The work is important for the research community which had been mainly using the simpler, unidirectional model to predict nanoscale multiferroic behavior.
2. On characterizing and improving the functionality of device components, I worked on four experimental projects.

• a. Enhanced the magnetoelectric coupling in a strain-mediated multiferroic composite systems by interposing a polymer thin film between magnetoelastic layer and ferroelectric single crystal. The work reported a nearly two fold increase in the sensitivity of the remanent magnetization in the magnetic layer to an applied electric field.
• b. Achieved tunable magnetoelastic effects in voltage-controlled exchange-coupled composite multiferroic microstructures with coupled magnetic bilayers. The findings are expected to be of great interest for the development of ultralow-power magnetoelectric memory devices. (Part of the work was also published in a conference paper -- 2018 PowerMEMS best paper finalist)
• c. Investigated the influence of nonuniform micron-scale strain distributions on the electrical reorientation of magnetic microstructures in multiferroic devices. This collaborated work highlighted the importance of surface and interface engineering on small length scales, and introduced a robust method to characterize future devices on micron-scale.
• d. Studied micro-strain distribution between patterned surface electrode arrays through x-ray microdiffraction and finite element simulations. The findings are relevant to the development of surface electrode based multiferroic devices with array-addressable localized strain control for applications including straintronic memory, probabilistic computing platforms, microwave devices, and magnetic-activated cell sorting platforms.

3. Multiferroics motor for cell and particle manipulation. Electrically controlled 20 um single magnetic domain Terfenol-D disks for cell manipulation, and micron-scale Ni and FeGa rings with nanoscale ring width for magnetic particle control

Dissertation Year Fellowship (2020-2021), UCLA.

TANMS CLIMB award in Graduate Research

Fellow, The Data Incubator

Edward K. Rice Outstanding M.S. Student Award for the UCLA Samueli School of Engineering, 2019. Link: UCLA ECE News.

2019 CESASC Scholarship -- Anna and John Sie Foundation Scholarship, Los Angeles, CA

Best Student Presentation Award Winner, 2019 Joint MMM-Intermag Conference, Washington, DC. Links: AIP Advances ALS, Berkeley Lab News, UCLA ECE News, TANMS Research Center News.

ALS Doctoral Fellow in Residence (2018-2019), Advanced Light Source, Lawrence Berkeley National Laboratory. Links: UCLA ECE News,TANMS Research Center News.

Distinguished Masters Thesis Award (2017-2018), Electrical & Computer Engineering, UCLA.

Big Data Fellowship, Bryn Mawr College & Center for Science and Information, 2015.

Science Horizon Fellowship, Howard Hughes Medical Institute (HHMI)/Bryn Mawr College, 2014.

Magnetism and Magnetic Materials Conference, Las Vegas, CA, USA, 2019; The 40th International Conference on Vacuum Ultraviolet and X-ray Physics, San Francisco, USA, 2019 -- "Electric-field controlled, exchange-coupled bilayer microstructures with tunable magnetoelastic effect" "

Joint Intermag-MMM Conference, Washington DC, USA, 2019, Best Student Presentation Award Winner -- "Single Domain Magnetoelastic Terfenol-D Microdisks for Particle and Cell Manipulation"

PowerMEMS Conference, Daytona Beach, FL, USA, 2018 Best Paper Finalist 1/8-- "Electric-field controlled magnetic reorientation in exchange coupled CoFeB/Ni bilayer microstructures"

Advanced Light Source Cross-Cutting Review, Berkeley Lab, CA, USA, 2017 -- “Effect of Non-Uniform Micron-Scale Strain Distributions on the Electrical Reorientation of Magnetic Micro-Structures in a Composite Multiferroic Heterostructure"

Annual Conference on Magnetism and Magnetic Materials (MMM), Pittsburgh, PA, USA, 2017 -- “Enhancement of coupling efficiency of ferroelectric to magnetoelastic thin film via interposing thin film polymer,”

Annual Conference on Magnetism and Magnetic Materials (MMM), New Orleans, LA, USA, 2016 -- “Modeling of domain wall motion in multiferroic heterostructures”

American Physics Society Mid-Atlantic Meeting, University Park, PA, USA, 2014 -- “Magnetic Properties of hexagonal HoFeO3 thin films”

American Physical Society, March Meeting, Baltimore, MD, USA, 2013 -- “Magnetization Reversal of Patterned Disks with Perpendicular Magnetic Anisotropy”

Selected Peer-Reviewed Journal Publications

Tunable Magnetoelastic Effect in Voltage-controlled Exchange-coupled Composite Multiferroic Microstructures

ACS Applied Material & Interfaces, American Chemical Society (2020).
Abstract: The magnetoelectric properties of exchange-coupled Ni-CoFeB-based composite multiferroic microstructures are investigated. The strength and sign of the magnetoelastic effect are found to be strongly correlated with the ratio between the thicknesses of the two magnetostrictive materials. In cases where the thickness ratio deviates significantly from one, the magnetoelastic behavior of the multiferroic microstructures is dominated by the thicker layer, which contributes more strongly to the observed magnetoelastic effect. More symmetric structures with thickness ratio equal to one show an emergent interfacial behavior which cannot be accounted for simply by summing up the magnetoelastic effects occurring in the two constituent layers. This new aspect is clearly visible in the case of ultrathin bilayers, where the exchange coupling drastically affects the magnetic behavior of the Ni layer, making the Ni/CoFeB-bilayer a promising new synthetic magnetic system entirely. This study demonstrates the richness and high tunability of composite multiferroic systems based on coupled magnetic bilayers compared to their single magnetic layer counterparts. Furthermore, due to the compatibility of CoFeB with present magnetic tunnel junction-based spintronic technologies, the reported findings are expected to be of great interest for the development of ultra-low-power magnetoelectric memory devices.

Bi-directional coupling in strain-mediated multiferroic heterostructures with magnetic domains and domain wall motion

Scientific Reports, Nature publishing (2018).
Abstract: Strain-coupled multiferroic heterostructures provide a path to energy-efficient, voltage-controlled magnetic nanoscale devices, a region where current-based methods of magnetic control suffer from Ohmic dissipation. Growing interest in highly magnetoelastic materials, such as Terfenol-D, prompts a more accurate understanding of their magnetization behavior. To address this need, we simulate the strain-induced magnetization change with two modeling methods: the commonly used unidirectional model and the recently developed bidirectional model. Unidirectional models account for magnetoelastic effects only, while bidirectional models account for both magnetoelastic and magnetostrictive effects. We found unidirectional models are on par with bidirectional models when describing the magnetic behavior in weakly magnetoelastic materials (e.g., Nickel), but the two models deviate when highly magnetoelastic materials (e.g., Terfenol-D) are introduced. These results suggest that magnetostrictive feedback is critical for modeling highly magnetoelastic materials, as opposed to weaker magnetoelastic materials, where we observe only minor differences between the two methods’ outputs. To our best knowledge, this work represents the first comparison of unidirectional and bidirectional modeling in composite multiferroic systems, demonstrating that back-coupling of magnetization to strain can inhibit formation and rotation of magnetic states, highlighting the need to revisit the assumption that unidirectional modeling always captures the necessary physics in strain-mediated multiferroics.

Cytocompatible magnetostrictive microstructures for nano- and microparticle manipulation on linear strain response piezoelectrics

Multifunctional Materials, IOP publishing. (2018)
Abstract: In this work, we investigate polycrystalline Ni and FeGa magnetostrictive microstructures on pre-poled (011)-cut single crystal [Pb(Mg1/3Nb2/3)O3]1−x-[PbTiO3]x (PMN-PT, x ≈ 0.31) with linear strain profile versus applied electric field. Magnetostrictive microstructure arrays with various geometries are patterned on PMN-PT. Functionalized magnetic beads are trapped by localized stray fields originating from the microstructures. With an applied electric field, the magnetic domains are actuated, inducing the motion of the coupled particles with sub-micrometer precision. This work shows promise of using energy-efficient electric-field-controlled magnetostrictive micro- and nanostructures for manipulating magnetic beads via a linear strain response. The work also demonstrates the viability of cells suspended in solution on these structures when subject to applied electric fields, proving the cytocompatibility of the platform for live cell sorting applications.

Influence of Nonuniform Micron-Scale Strain Distributions on the Electrical Reorientation of Magnetic Microstructures in a Composite Multiferroic Heterostructure

Nano Letter, American Chemical Society (2018).
Abstract: Composite multiferroic systems, consisting of a piezoelectric substrate coupled with a ferromagnetic thin film, are of great interest from a technological point of view because they offer a path toward the development of ultralow power magnetoelectric devices. The key aspect of those systems is the possibility to control magnetization via an electric field, relying on the magneto-elastic coupling at the interface between the piezoelectric and the ferromagnetic components. Accordingly, a direct measurement of both the electrically induced magnetic behavior and of the piezo-strain driving such behavior is crucial for better understanding and further developing these materials systems. In this work, we measure and characterize the micron-scale strain and magnetic response, as a function of an applied electric field, in a composite multiferroic system composed of 1 and 2 μm squares of Ni fabricated on a prepoled [Pb(Mg1/3Nb2/3)O3]0.69–[PbTiO3]0.31 (PMN–PT) single crystal substrate by X-ray microdiffraction and X-ray photoemission electron microscopy, respectively. These two complementary measurements of the same area on the sample indicate the presence of a nonuniform strain which strongly influences the reorientation of the magnetic state within identical Ni microstructures along the surface of the sample. Micromagnetic simulations confirm these experimental observations. This study emphasizes the critical importance of surface and interface engineering on the micron-scale in composite multiferroic structures and introduces a robust method to characterize future devices on these length scales.

Pilot New High School Outreach Program, CA (2016-2018)

• Developed curriculum and co-taught interdisciplinary classes to 200 students at Lawndale High School in Centinela Valley High School District, Los Angeles.
• Coordinated with high school science teachers to revise curriculum.

Research Mentor for REU/URP/YSP students from underrepresented groups (2019 - 2021)

• Mentored three students from community college and high school for a 10-week research experiences for undergraduate program (REU) and young scholars program (YSP)
• Co-led a team of 16 students from Los Angeles colleges and high schools to D.C. for the Emerging Reserchers National (ERN) Conference in STEM.
• Engaged in professional development panel discussions for mentors and educators with NSF EFRI/ERC program managers
• Mentored three UCLA engineering undergraduate students on research and co-written a journal manuscript (under review). One of the students are the first co-author of the paper.