Brian Lejeune

Brian Lejeune
Post-Doctoral Researcher, Part-time Lecturer
Chemical Engineering


B.S. Chemical Engineering from Northeastern University; Boston, MA 2013
Ph.D. Chemical Engineering from Northeastern University; Boston, MA 2019

Currently as a post-doctoral researcher I am evaluating the biocidal capabilities of Cu2O for use in antimicrobial coatings by obtaining fundamental correlations between its electronic state, crystal lattice condition and antimicrobial response. The current COVID-19 pandemic has shed light on the need for passive antimicrobial surfaces that down regulate the transmission of pathogens through touching commonly encountered surfaces such as handrails and door handles, without requiring external activation or chemicals for sanitation. Cu-based materials have been accepted as having antimicrobial properties for centuries, but to date the underlying mechanism is not fully understood. The current work is at the intersection of Materials Science and Bioengineering, where the role of defect engineering in Cu2O will be evaluated as a possible mechanism for enhancement of biocidal activity. Ultimately we strive to gain a deeper understanding of the mechanism of biocidal activity in Copper oxides.

My dissertation entitled: “Composition-Lattice Interactions in Intermetallic Ferromagnetic Systems quantified the role of detailed chemistry on tuning the crystal structures and magnetic phase transitions in intermetallic ferromagnetic systems. My work focused primarily on the orthorhombic cmmm-type AT2X2 (A = Al, Ga, Ge; T = Mn, Fe, Ni, Co; X = B, C) system which has received interest as a novel rare-earth-free magnetocaloric material for room thermal management applications. The magnetocaloric effect (MCE) is the reversible adiabatic temperature change (ΔTad) of a magnetic material upon the application or removal of a magnetic field (Happ). The MCE is the mechanism underlying magnetic refrigeration – an emerging energy-efficient, environmentally-friendly alternative to vapor-compression cooling technology. AlFe2B2 is reported to have a MCE (ΔTad~1.8 K at Happ=1.95 T) that exceeds that of any intermetallic boride of 1-2-2 type, and is comprised of lightweight, inexpensive, earth-abundant elements providing motivation for this research.

Figure 1 M(T) curve at 2 T upon heating through the phase transition (Tt ~ 300 K)

Prior to my dissertation only 3 papers were published on the AlFe2B2 system and the mechanism underlying the observed magnetocaloric effect was not well understood. Correlations made between crystal structure, microstructure, composition, magnetism, and thermal behavior provide insight into the fundamental driving forces underlying the magnetocaloric response of AlFe2B2, and related transition-metal borides. Contributions of this work include developing trends for tuning the magnetic transition temperature (260 K < TC < 320 K) in the AT2X2 system through compositional modification and describing the lattice-magnetism interactions resulting from these substitutions. Additionally, through Bridgman single crystal growth and characterization of AlFe2B2 compound at the Ames Laboratory as part of a DOE Science Graduate Research Fellowship (SCGSR), it was identified that minor Al-Fe antisite substitution was possible and that very minor substitutions (~2 at. %) led to significant changes in the magnetic phase transition temperature (280 K < TC < 315 K) and observed magnetocaloric effect (2.3 < ΔS < 4.0 J/mol-K). The anisotropic transport properties of this compound were also investigated in crystallographically oriented samples including the thermal conductivity, electrical resistivity, and Seebeck coefficient as a function of temperature.

Figure 2 Trends in the AlT2B2 (T = Mn, Fe, Ni, Co) system showing the effect of transition metal interatomic distance on the magnetic phase transition temperature

Figure 3 Enhancement in the magnetocaloric effect of AlFe2B2 is observed in Fe-enriched samples relative to their Al-rich and stoichiometric counterparts

I was raised in a rural town in Rhode Island and have always enjoyed being immersed in nature. I am an Eagle Scout and love hiking, skiing, and camping. I am the mineral curator for Lafayette College in Easton, PA and an avid mineral collector. I have been mining several times for quartz, amethyst, and fossils. Traveling both inside and outside the country is a passion of mine and has helped me to develop a more global perspective. I love cooking and try to maintain a healthy lifestyle by practicing yoga and meditate every day. My inspiration for becoming an engineer was to potentially aid in solving environmental issues in the world.

Experimental Techniques:
Arc-melting, Suction casting, Bridgman single crystal growth, X-ray Diffraction (XRD), Synchrotron X-ray Diffraction, Rietveld refinement, Laue backscattered diffraction, Scanning Electron Microscopy (SEM), Quantitative Electron Dispersive Spectroscopy (EDS), Vibrating Sample Magnetometer (VSM), SQUID Magnetometer, Differential Scanning Calorimetry (DSC), Electrical Discharge Machining (EDM), Thermal and Electrical Transport, Origin Lab, LabVIEW, MATLAB

Professional Membership:
Society of Mineral Museum Professionals (SMMP)
Mineralogicial Society of America
American Institute of Chemical Engineering
IEEE Magnetics Society
American Physical Society
Materials Research Society

X. Zhang, B.T. Lejeune, R. Barua, L. H. Lewis, “Estimating the in-operando stabilities of AlFe2B2-Based Compounds for Magnetic Refrigeration,” Journal of Alloys and Compounds 823 (2020).

Lejeune, B.T., Jensen, B.A., Schlagel, D.L., Lograsso, T.A., Kramer, M.J., Lewis, L.H., “Effects of Al and Fe solubility on the magnetofunctional properties of AlFe2B2, Physical Review Materials (2019).

Lejeune, B.T., Barua, R., Stonkevitch, E., Kramer, M.J., McCallum, R. W., Lewis, L. H., “Magnetostructural transition temperature trends in Al(Fe,T)2X2 compounds,” Journal of Magnetism and Magnetic Materials (2019).

Barua, R., Lejeune, B.T., Ke, L., Jensen, B. A., Levin, E., McCallum, R. W., Kramer, M. J., Lewis, L. H., “Enhanced room-temperature magnetocaloric effect and tunable magnetic response in Ga-and Ge-substituted AlFe2B2 alloys,” Journal of Alloys and Compounds (2018).

Lejeune, B.T., Du, X., Barua, R., Zhao, J.C., Lewis, L. H., “Anisotropic Thermal Conductivity of Magnetocaloric AlFe2B2” Materialia 1 (2018) 150-154.

Barua, R., Lejeune, B. T., Ke, L., Hadjipanayis, G., Levin, E. M., McCallum, R. W., Kramer, M. J., Lewis, L. H., “Anisotropic Magnetocaloric Response in AlFe2B2,” Journal of Alloys and Compounds 745 (2018) 505-512.

Levin, E. M., Kramer, M. J., Jensen, B. A., McCallum, R. W., Howard, A., Barua, R., Lejeune, B., Lewis, L. H., “Effects of Al content and annealing on the phases formation, lattice parameters, and magnetization of AlxFe2B2 (x = 1.0, 1.1, 1.2) alloys,” Physical Review Materials 2 (2018) 1-9.

Lejeune, B.T., Barua, R., McDonald, I.J., Gabay, A.M., Lewis, L.H., Hadjipanayis, G.C., “Synthesis and processing effects on magnetic properties in the Fe5SiB2 system,” Journal of Alloys and Compounds 731 (2018) 995-1000.

Stephen, G. M., McDonald, I., Lejeune, B., Lewis, L. H., Heiman, D., “Synthesis of low-moment CrVTiAl: A potential room temperature spin filter,” Applied Physics Letters 109, (2016).

Lewis, L., Barua, R., Lejeune, B., “Developing magnetofunctionality: Coupled structural and magnetic phase transition in AlFe2B2,” Journal of Alloys and Compounds 650 (2015) 482 – 488.

Hamilton, C., Lejeune, B.T., Rosengaus, R., “Trophallaxis and prophylaxis: social immunity in the carpenter ant Camonotus pennsylvanicus,” Biology Letters 7 (1) (2011) 89-92.

Selected Presentations:
X. Zhang, Brian Lejeune, R. Barua, R. W. McCallum, L. H. Lewis, “Investigating the Mechanical and Chemical Stability of AlFe2B2-Based Compounds for Magnetic Refrigeration,” Intermag - Magnetism and Magnetic Materials, Washington D.C. January 2019.

Brian Lejeune, S. Thimmaiah, I. J. McDonald, A. M. Gabay, M. J. Kramer, L. H. Lewis, G. C. Hadjipanayis, “Magnetic and Structural Parameters of Fe5(Si0.75Ge0.25)B2 single crystals,”  Intermag - Magnetism and Magnetic Materials, Washington D.C. January 2019.

Brian Lejeune, D. L. Schlagel, B. A. Jensen, T. A. Lograsso, M. J. Kramer, L. H. Lewis, Effects of Al and Fe solubility the on magnetocaloric properties of AlFe2B2,” Intermag - Magnetism and Magnetic Materials, Washington D.C. January 2019.

Brian Lejeune, Radhika Barua, E. Stonkevitch, L. H. Lewis, Connecting Composition, Structure and Magnetic Transitions in AlT2B2 Compounds,” Magnetism and Magnetic Materials, Pittsburgh, PA, November 10, 2017.

Radhika Barua, Brian Lejeune, Liqin Ke, E. M. Levin, M. J. Kramer, R. W. McCallum, L. H. Lewis, L. H., “Anisotropic Magnetocaloric Effect in Layered AlFe2B2,” Intermag 2017, Dublin, Ireland, April 25, 2017.

Brian Lejeune, G. Hadjipanayis, L.H. Lewis, “Large Magnetocrystalline Anisotropy in AlFe2B2 Single Crystals” Magnetism and Magnetic Materials, New Orleans, LA, November 1, 2016.

Brian Lejeune, L. H. Lewis, “Elemental Substitution for Designing ‘Cool’ New Materials: AlFe2B2 Structure-Magnetism Relationships for MCE Applications,” GE Global Research Summit, Niskayuna, NY, August 12, 2016

Brian Lejeune, Radhika Barua, L. H. Lewis, “Investigating Layered Al(Fe1-xMnx)2B2 Compounds for Structure – Composition – Magnetic Property Correlations,” IEEE Magnetics Summer School, Minneapolis, MN, June 16, 2015.

Brian Lejeune, Radhika Barua, Enric Stern Taulats, Lluis Manosa, Antoni Planes, L. H. Lewis,  “First-Order Magnetostructural Phase Transition in AlFe2B2,” APS March Meeting, San Antonio, TX, Mar. 5, 2015.

Brian Lejeune, Radhika Barua, and L.H. Lewis, “Understanding Structure-Magnetic Property Correlations in AlFe2B2 for Magnetocaloric Applications,” MRS Fall Meeting, Boston, MA, Dec. 5, 2014.

Brian Lejeune, Radhika Barua, L.H. Lewis, “Designing ‘Cool’ Magnetic Materials for Efficient Refrigeration: Tailoring AlFe2B2 Magnetism-Structure Relationships for Magnetocaloric Applications,” Boston Regional Nanomagnetism Workshop, Boston, MA, Apr. 4, 2014.