Strong spin-phonon coupling is responsible for a wide range of scientifically rich and technologically important phenomena—including multiferroic properties, magnetically tuned shape-memory effects, magnetothermal, and magnetodielectric behavior. To clarify the microscopic origins of magneto-electric behavior in strongly spin-phonon coupled materials, we have used combined high- pressure- and -magnetic-field-tuned inelastic light scattering to investigate the pressure/field/temperature (PHT) phase diagram of the magnetically frustrated magnetodielectric spinel, Mn 3 O 4. Among the key results of this study (M. Kim et al., submitted to Phys. Rev. Lett.): (1). Applied pressure rotates the magnetic easy axis of Mn 3 O 4 in the direction of the strain field (Fig. (c)), suggesting that it is possible to engineer the magnetism and modify the dielectric properties of this material via epitaxial strain in thin films. (2). Simultaneous applied pressure and magnetic field generates a frustrated phase region (II in (d)) in which a disordered magnetic state persists to T~0K. (3). Simultaneous pressure and field measurements reveal a route to generating a continuous quantum phase transition between magnetostructural phases. (a) Illustrations of various magnetostructural configurations of Mn 3 O 4 that we’ve produced with pressure and magnetic field. (b) Contour pl ot of the T 2g phonon mode intensity as functions of energy and applie d magnetic field (H||[1-10]), where red=maximum counts and blue=0 counts. (c) Contour plot of the phonon mode intensities as functions of energy and applied pressure (P||[110]) for T=39K and H=0T. (d) C ontour plot of the phonon mode intensities as functions of energy and applied magnetic field (H||[110]) for T=39K and P=16kbar. Pressure- and field-tuning the magnetostructural phases and properties of the magnetodielectric spinel Mn 3 O 4 S. Lance Cooper, University of Illinois, Urbana-Champaign, DMR

Noteworthy “broader impacts” this year: (1). Single-crystal growth and distribution - We have used a variety of methods to grow high quality single crystal samples of several materials, including Mn 3 O 4 (Fig. (a), left) and KCuF 3 (Fig. (a), right), which we have distributed to many other groups in the community, e.g., Peter Abbamonte, U. of Illinois, Christie Nelson, Brookhaven NL, Gang Cao, U. of Kentucky, Raffi Budakian, U. of Illinois, and Z.X. Shen. (2). Student training - This grant supported the PhD thesis work of two female graduate students from the U. of Illinois (Fig. (b)), Minjung Kim and Yewon Gim, and an undergraduate student, Mike Witek. All gained training in single crystal growth, X-ray diffraction and magnetic characterization, high pressure- and magnetic-field methods, and optical spectroscopic methods, and obtained practice giving scientific presentations via group meetings and conference presentations. (3). Review article – I wrote a Raman scattering review article, 'Raman scattering as a tool for studying complex materials,' which is a guide for setting up a Raman scattering system, emphasizing high pressure and high magnetic field Raman measurements, i.e., the centerpiece of this research grant. This review article was published in 'Optical techniques for materials characterization' (Taylor & Francis, 2011) (Fig. (c)). (3). Outreach activities – In Fall ‘10, I gave a public lecture to ~150 people ranging from K-12 to senior citizens on 'Using Light and Color in Science and Nature' in Fall '10 as part of the UIUC Dept. of Physics' Saturday Physics Honors Program. Grad student Minjung Kim Large single crystals of (left) Mn 3 O 4 and (right) KCuF 3 grown in our lab using different methods (a) (b) Grad student Yewon Gim Cover of “Optical techniques for materials characterization,” published in 2011, in which PI Cooper contributed a Raman scattering review article featuring several elements of this NSF grant. (c) Pressure- and field-tuning the magnetostructural phases and properties of the magnetodielectric spinel Mn 3 O 4 S. Lance Cooper, University of Illinois, Urbana-Champaign, DMR