Coherent spin oscillations and non-linear dynamics in two quantum magnets

I present experimental studies of the low-temperature linear and nonlinear AC magnetic behavior of two insulating magnetic materials: the dilute Ising magnet Lithium Yttrium Holmium Tetraflouride (LiHo0.045Y0.955 F4); and the frustrated Heisenberg magnet Neodymium Gadolinium Gallium Garnet (NdxGd3-xGa5O12 for x={0.01, 0.05, 0.1}). We find that under certain thermodynamic limits, LiHo 0.045Y0.955F4 can be continuously tuned between competing low-temperature states by cooling the sample in an external, DC magnetic field. Furthermore, we demonstrate the magnetic pump/probe technique as a powerful tool to quantify the stability of the magnetic state in the presence of disorder, and to probe the coupling between the spin states and the incoherent nuclear spin bath. In addition, I present susceptibility data for the three different concentrations of NdxGd3-x Ga5O12, which show that the doped samples possess the same coherent spin degrees of freedom as is seen in the pure sample. We find that even in the lightest-doped sample (0.1%), the presence of disorder suppresses the onset of Antiferromagnetic order by a factor of two, and that any transition in the other samples (0.5% and 1%) must be below 50 mK.