Sanhita Ghosh

Multi-frequency EPR studies of a mononuclear holmium single-molecule magnet based on the polyoxometalate [HoIII(W5O18)2]9−

Continuous-wave, multi-frequency electron paramagnetic resonance (EPR) studies are reported for a series of single-crystal and powder samples containing different dilutions of a recently discovered mononuclear Ho(III) (4f(10)) single-molecule magnet (SMM) encapsulated in a highly symmetric polyoxometalate (POM) cage. The encapsulation offers the potential for applications in molecular spintronics devices, as it preserves the intrinsic properties of the nanomagnet outside of the crystal. A significant magnetic anisotropy arises due to a splitting of the Hunds coupled total angular momentum (J = L + S = 8) ground state in the POM ligand field. Thus, high-frequency (50.4 GHz) EPR studies reveal a highly anisotropic eight line spectrum corresponding to transitions within the lowest m(J) = ±4 doublet, split by a strong hyperfine interaction with the I = 7/2 Ho nucleus (100% natural abundance). X-band EPR studies reveal the presence of an appreciable tunneling gap between the m(J) = ±4 doublet states having the same nuclear spin projection, leading to a highly non-linear field-dependence of the spectrum at low-frequencies.

Electron magnetic resonance studies of the Pr3Ga5SiO14 and Nd3Ga5SiO14 kagomé systems

We report low-temperature, high-frequency (50–800 GHz) electron magnetic resonance measurements on single crystals of the antiferromagnetic kagome lattice compounds Nd3Ga5SiO14 and Pr3Ga5SiO14. The obtained spectra are extremely rich, displaying a large number of sharp peaks whose positions exhibit a strong systematic temperature dependence. In contrast, the spectra do not seem to follow any systematic dependence on the microwave frequency. This leads us to conclude that the observed features are quite different from conventional independent-particle electron paramagnetic resonance transitions, arising instead from collective excitations associated with finite-sized antiferromagnetically ordered clusters.