NEU
Nanomagnetism Group
research

Lewis Lab    |    Heiman Lab

Lewis Lab

The Lewis Lab research program focuses on the synthesis and characterization of magnetic nanomaterials in bulk and in thin films, with the goal of elucidating fundamental information to enable advanced applications towards energy management, multifunctional devices and biomedical applications. Currently, our lab focuses on projects examining magnetostructural transitions, complex oxide films, advanced permanent magnet nanomaterials, ferromagnetic semiconducting nanomaterials and magnetic nanoparticles.

Our lab, in collaboration with the Heiman Lab, carries out materials synthesis as well as characterization and analyses. Synthesis methods available to the group include arc-melting, rapid solidification (melt-spinning), and thin film synthesis via Molecular Beam Epitaxy (MBE), thermal evaporation, and anodization. Characterization of the magnetic and phase state is carried out via X-ray diffraction (XRD), electron microscopy, scanning probe microscopy, magnetometry (Superconducting Quantum Interference Device (SQUID) and alternating gradient magnetometry, and thermal analysis. Synchrotron-based spectroscopy and scattering probes are also employed for advanced materials characterization.

Projects

Advanced permanent magnets are utilized in our everyday lives, with applications that encompass motors, speakers, hybrid vehicles and wind turbines. Rare earth elements are frequently utilized in their production as their properties lend significant anisotropies and large energy products in permanent magnets. Lewis’ group research in this field focuses on an understanding the effects of microstructure and nanostructure of magnetic compounds and assemblages on the performance of the magnetic material. A few examples are provided here:

Rare-Earth-Free Advanced Permanent Magnets: Current economic and geopolitical trends suggest that future production of rare earth elements will not be able to keep up with global demand. To that end, we seek to produce nanostructured permanent magnets that do not utilize rare-earth elements but produce comparable anisotropies and energy products. This project is funded by the Office of Naval Research under Grant No. N00014-10-1-0553 and the National Science Foundation under Grant No. 1129433.

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF) or the Office of Naval Research (ONR).

Multiscale Development of L10 Materials for Rare-Earth-Free Permanent Magnets: The tetragonal L1o crystal structure occurs naturally in meteorites and imparts high magnetization and anisotropy. We are currently investigating the iron-nickel L10-type crystal structure and interstitially-modified L10-type MnAl-based systems. This research is funded by the ARPA-E REACT program under Grant No. 0472-1537

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of Energy (DOE).

Exchange Coupling in Magnetic Nanocomposites: Local magnetic interactions between magnetic components exchange-spring systems strongly depend upon the chemical and topographical nature of the interface. Relationships between the exchange coupling, the microstructure and the magnetic response have been studied in a variety of technologically-relevant materials. In particular, the stability and character of the exchange coupling in the system Nd2Fe14B/α-Fe has been uniquely quantified with recoil curves, an advance beyond the standard assessment using the remanence ratio Brecoil/Br that highlights the origins of the differences in their technical magnetic behavior and suggest structural modification pathways for property improvement. (C. L. Harland, L. H. Lewis, Z. Chen and B.-M. Ma, “Exchange coupling and recoil loop area in Nd2Fe14B nanocrystalline alloys”, J. Magn. Magn. Mater., 271 (1) April 2004, Pages 53-62.)

micrograph

recoil loop

Fig 5:  TEM micrograph of nanocrystalline Nd9Fe86B5

Fig. 6:  Recoil loop remanence ratio Brecoil/Br as a function of reverse internal field for the Nd9Fe86B5 and Nd2Fe14B samples at a selection of temperatures

 

Manipulation of the Interphase Interface: The relationship between the condition of the interphase interface and the resultant magnetic exchange coupling in magnetic “exchange-spring” nanocomposites was investigated in structurally well-characterized ferromagnetic model bilayers of thin film L10-CoPt/Co bilayers and of epitaxial SmCo/Fe bilayers investigated. The results and analyses point to a method of determining the relationship between the strength of the interphase magnetic exchange coupling in exchange-spring magnetic systems and the interphase registry (L. H. Lewis, J.Kim, K. Barmak and R. Ristau, “The CoPt System: A Natural Exchange Spring”; Physica B 327 190-193 (2003); L. H. Lewis, J. Kim, K. Barmak, and D. C. Crew, “Interphase Exchange Effects in CoPt/Co Bilayer Thin Films”; J Phys. D: Applied Physics 37 (19) (7 October 2004) 2638-2642; K. Kang, L. H. Lewis, J. S. Jiang and S. D. Bader, “Recoil hysteresis of Sm-Co/Fe exchange spring bilayers”, J. Appl. Phys., 98 113906 (2005))

recoil curves

Room-temperature recoil curves obtained from the CoPt(25 nm)/Co(16.7 nm) bilayer film sample subjected to different annealing treatments, as labeled  Note the change of the recoil curve width with annealing treatment


 

Magnetostructural materialsexhibit simultaneous magnetic and structural phase changes of an abrupt and hysteretic nature that are fundamentally different from the canonical ferromagnetic transition of second-order thermodynamic character, such as that exhibited by iron, for example. The binary alloy iron-rhodium (FeRh) undergoes a ferromagnetic/antiferromagnetic phase transition. That displays unique responses placed under physical, thermal, or magnetic strain or subjected to nanostructuring. This makes FeRh an ideal material for various sensing technologies. Our research aims to better understand the various characteristics of this alloy in nanostructured form, based upon work supported by the U.S. Department of Energy - Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Grant No. DE-SC000525. In addition, a collaboration with Brookhaven National Laboratory and the University of Leeds, U.K. to study FeRh properties in the layered thin film form is sponsored by the National Science Foundation under Grant No. DMR-0908767

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF) or the Department of Energy (DOE).

FeRH
FeRhB
FeRh magnetic transition from antiferromagnetic
to ferromagnetic in an applied field of 0.1 T.
  Corresponding structural transition
as a function of temperature


Complex Oxide materials are capable of exhibiting two or more ferroic features such as ferromagnetism, ferroelectricity, or ferroelasticity. They have strong potential for a broad range of applications, which include multiple state memory storage devices, networked environmental sensors and spintronic devices. Our lab focuses on thin films of complex oxides, such as (La,Sr)MnO3 (LSMO) to better understand their physical and magnetic properties and how changing them affects their multiferroic capability. This research is sponsored by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

lsmo
Schematic of A-site ordered and A-site LSMO in the film form.

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Department of Energy.



Titania Nanotubes arrays doped with iron are anticipated to exhibit multifunctional behavior that combines effects from electronic charge, magnetic spin and optical response. Properly engineered, these materials hold promise for potential application in devices to efficiently absorb and transfer solar energy and/or to process data with increased speed, precision and accuracy. This project is sponsored by the National Science Foundation under Grant No DMR-0906608.

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

American Physical Society (APS) March meeting 2012

SEM image Titania
SEM image of a bundle of Titania nanotubes


Magnetic nanoparticle-based microfluidic separation of circulating tumor cell populations enables understanding of the spreading of cancer and fosters development of various drug strategies. In this work we developed a microfluidic magnetic-activated cell sorting (MACS) system using a "bottom-up" approach employing both computational and experimental approaches to lead to optimized elements of device design. This work is carried out in collaboration with Prof. Shashi Murthy, Northeastern University.

 

MACS apparatus schematic
A schematic of a MACS apparatus