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VERSION:2.0
PRODID:-//RLASKEY//CALENDEROUS//EN
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BEGIN:VEVENT
DTSTAMP:20260915T010516Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20121207T170000Z
DTEND:20121207T180000Z
UID:event961@bu.edu
URL:http://physics.bu.edu/internal/events/show/961
SUMMARY:Optical properties of iron oxides: the new iron age
DESCRIPTION:Featuring Janice Musfeldt\, Department of Chemistry\, Universit
	y of Tennessee\nHosted by: Richard Averitt\n\nPart of the Biophysics/Conden
	sed Matter Seminar Series.\n\nAbstract\nMagnetoelectric coupling in materia
	ls like multiferroics\, dilute magnetic semiconductors\, and topological in
	sulators has attracted a great deal of attention\, although most work has b
	een done in the static limit. Optical spectroscopy offers a way to investig
	ate the dynamics of charge-spin coupling\, an area where there has been muc
	h less effort. Using these techniques\, we discovered that charge fluctuati
	on in LuFe2O4\, the prototypical charge ordered multiferroic\, has an onset
	 well below the charge ordering transition\, supporting the “order by
	 fluctuation” mechanism for the development of charge order superstru
	cture. Bragg splitting and large magneto-optical contrast suggest a low tem
	perature monoclinic distortion that can be driven by both temperature and m
	agnetic field. At the same time\, dramatic splitting of the LuO2 layer phon
	on mode is attributed to charge-rich/poor proximity effects\, and its tempe
	rature dependence reveals the antipolar nature of the W layer pattern. Usin
	g optical techniques\, we also discovered that α-Fe2O3\, a chemically
	-similar parent compound and one of the world's oldest and most iconic anti
	ferromagnetic materials\, appears more red in applied magnetic field than i
	n zero field conditions. This effect is driven by a field-induced reorienta
	tion of magnetic order. The oscillator strength lost in the color band is p
	artially transferred to the magnon side band\, a process that also reveals 
	a new exciton pattern induced by the modified exchange coupling. Analysis o
	f the exciton pattern exposes C2 monoclinic symmetry in the high field phas
	e of hematite. Finally\, we examine the optical properties of NiFe2O4\, a m
	agnetic oxide of interest for spintronic applications. Comparison with firs
	t principles electronic structure calculations reveals a band gap hierarchy
	 that may provide new opportunities for spin polarized light harvesting. Ta
	ken together\, these findings advance our understanding of iron-based mater
	ials under extreme conditions.\nCoworkers: X. S. Xu\, P. Chen\, B. Q. &ndas
	h;C. Sun\, B. Holinsworth\, K. O’Neal\, T. V. Brinzari (Tennessee); S
	. McGill (NHMFL); J. De Groot\, M. Angst\, R. P. Hermann (Julich); A. D. Ch
	ristianson\, B. C. Sales\, D. Mandrus (ORNL); A. P. Litvinchuk (Houston); J
	. –W. Kim (Ames); Z. Islam (Argonne); N. Lee\, S. –W. Cheong (R
	utgers); D. Mazumdar\, A. Gupta\, H. Sims\, W. H. Butler (Alabama).\n 
	\nSupport: Materials Science Division\, Basic Energy Sciences\, U. S. Depar
	tment of Energy.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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