I will discuss recent multi-high-frequency EPR studies of several fascinating molecule-based nanomagnets comprised of single metal ions that exhibit strong spin-orbit anisotropy. These include: Ho3+ (4f10) encapsulated in a W10O36 polyoxometallate (POM) cage [1]; an unusual trigonal Ni2+ complex [2]; and several tetranuclear Co2+ (3d7) SMMs [3]. Most of the talk will be devoted to the Ho3+ system, in which the magnetic anisotropy arises due to a splitting of the Hund's coupled J (= L + S) ground state in the POM ligand field. EPR studies reveal a highly anisotropic eight line spectrum corresponding to transitions within the lowest mJ = �4 doublet, split by a very strong and anisotropic hyperfine interaction with the I = 7/2 Ho nucleus. Remarkably, electron-spin-echo measurements allow detailed studies of the coherent, coupled electron-nuclear spin dynamics, including Rabi oscillations, ESEEM, and evaluation of T2. Results will be compared for different hyperfine transitions (different ?mI selection rules) and [HoxLn1-x] dilutions. Time allowing, I will discuss the characterization of several highly anisotropic Ni2+ and Co2+ species using very high magnetic fields and multi-high-frequency EPR techniques, enabling evaluation of zero-field-splitting parameters possessing first-order spin-orbit contributions. An example will be given where a negative axial D parameter exceeding 100 cm-1 was inferred from high-field EPR measurements [2].Work performed in collaboration with: E. Coronado, A. Gaita-Ari�o, S. Cardona-Serra (U. Valencia); T. Mallah, L. Batchelor (U. Paris - Sud); J. Zadrozny, J. R. Long (UC Berkeley); M. Murugesu, F. Habib (U. Ottawa); J. Liu, S. Ghosh. M. Shiddiq (NHMFL and Florida State University).[1] S. Ghosh et al., Dalton Trans. 41 , 13697 (2012).      [2] R. Ruamps et al., J. Am. Chem. Soc. 135 , 3017 (2013).[3] J. M. Zadrozny et al., Chem. Commun. 48 , 3927 (2012).

EPR studies of highly anisotropic mononuclear nanomagnets

246th National Meeting (2013)

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