Frustration in the Magnetic Molecules W72V30 and Pr13 Probed by NMR and Tunnel-diode Resonator

The magnetic molecules Pr13 and W72V30 have been studied by DC and AC magnetic susceptibilities and NMR. These molecules exhibit geometrical frustration resulting from antiferromagnetic intramolecular coupling of nearest neighbor paramagnetic ions. In Pr13, 12 PrIII ions (S=1) interact along edge sites of an icosahedron centered about an additional PrIII ion. For W72V30, 30 VIV ions (S=1/2) interact along corner sharing sites of a near perfect icosidodecahedron, a spherical representation of a 2-D Kagome Lattice. Characterizing the DC magnetic response requires a distribution of exchange constants for both molecules at low temperatures. Results are compared to similar frustrated systems which feature a variety of magnetic phenomena - metamagnetic phase transitions, magnetic hysteresis without anisotropy, spin glass behavior, and superparamagnetism.