Komalavalli Thirunavukkuarasu

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We present recent studies on the nature of spin-phonon exchange interactions indifferent classes of magnetic materials using magneto-Ramanspectroscopy. Thefirst compound that will be discussed is SrCu2(BO3)2.It is a quasi-2D orthogonal spin dimer system with a spinsinglet ground state and considered as typical example for the realization of the Shastry-Sutherland model and exhibits a sequence of magnetization plateau at magnetic fields higher than 20 T,i.e., high enough to close the low temperature spin gap. The unique behavior ofthis quantum spin liquidresults from the interplay between geometrical frustration andstrong quantumfluctuations. The origin and characteristics of the strongspin-latticecoupling in SrCu2(BO3)2revealed by Ramanscattering studies at high magnetic fields up to 45T will bepresented. Theinterpretation of experimental results is supported by atheoretical analysisand prediction of active Raman modes that include theso-called pantograph mode[1]. The second compound is [(CH3)2NH2]Co(HCOO)3belonging to the family of multiferroic metal organicframeworks (MOF). In theinfrared studies under applied magnetic fields upto 35T, itwas concluded thatCo MOF adopts a different mechanism for facilitatingsaturation of magneticstates by involving formate stretching distortions unlikeother complexes inthe family that use the formate bending mode. We performedRaman spectroscopyon [(CH3)2NH2]Co(HCOO)3at magneticfields up to 31T to probe the magneto-elastic coupling. It wasfound that aweak Raman active vibrational mode at about 798 cm-1correspondingto symmetric bending of the formate ion does exhibitmagnetic-field-inducedfrequency shifts [2]. Lastly,we will present CoII(acac)2(H2O)2(acac = acetylacetonate) which is a molecular magnet. We were able to show forthe first timedistinct couplings of g phonons of and its deuterated analogswithzero-field-split, excited magnetic/spin levels (Kramersdoublet (KD)) of the S= 3/2 electronic ground state. The couplings are observed asavoided crossingsin magnetic-field-dependent Raman spectra with couplingconstants of 1–2 cm−1[3]. The results of ourinvestigations and itsimplications will be discussed in detail in thispresentation. [1] K.Thirunavukkuarasu,G. Radtke, Z. Lu, M. Lazzeri, P. C. M. Christianen, M. V.Ballottin, H. A.Dabkowska, B. D. Gaulin, D. Smirnov, M. Jaime, and A. Saúl,Physical Review B 107,064410 (2023). [2] K.Thirunavukkuarasu,R, Richardson, Z. Lu, D. Smirnov, N. Huang, N. Combs, G.Pokharel, and D.Mandrus, AIP Advances, 2021, 11, 015040 (2021). [3] D.Moseley, S.Stavretis, K. Thirunavukkuarasu, M. Ozerov, Y. Cheng,L. Daemen, J.Ludwig, Z. Lu, D. Smirnov, C. Brown, A. Pandey, A. J.Ramirez-Cuesta, A. Lamb,M. Atanasov, E. Bill, F. Neese, Z. Xue, Nature Communications, 2018, 9,2572 (2018).

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Department of Physics, Florida A & M University, Tallahassee, FL, USA NationalHigh Magnetic Field Laboratory, Tallahassee, FL, USA
PH2
Contact: Markus Grüninger / Matteo